XXVI International Horticultural Congress: IV International Symposium on Taxonomy of Cultivated Plants, 2004
Cucurbita pepo (pumpkin, squash, gourd) is extremely variable in fruit characteristics. According... more Cucurbita pepo (pumpkin, squash, gourd) is extremely variable in fruit characteristics. According to recent botanical and cultivated-plant taxonomical treatments that were based on variations in allozymes and fruit shape, C. pepo consists of three subspecies containing wild and cultivated, inedible, small-fruited sorts (gourds) and eight groups of edible, large-fruited cultivars (pumpkins and squash). Our objective was to determine if these treatments reflect genetic relationships as viewed at the DNA level, through the use AFLP, ISSR, and SSR markers. Forty-five accessions were compared for presence or absence of 448 AFLP, 147 ISSR, and 20 SSR bands, their genetic distances (GDs) were estimated, and UPGMA cluster analysis was conducted. Correlation coefficients were 0.95 between AFLPs and ISSRs, 0.78 between AFLPs and SSRs, and 0.77 between ISSRs and SSRs, all three comparisons with P << 0.001. Overall, clustering and sub-clustering were much in accordance with two highly polygenic characteristics, fruit shape and size. Clustering occurred in accordance with subspecies and sub-clustering in accordance with cultivar-groups. Within-group GDs were less than corresponding between-group GDs in nearly all comparisons. The smallest-fruited accession, 'Miniature Ball', occupied a central position within C. pepo.
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik, 2003
Cucurbita pepo (pumpkin, squash, gourd), an economically important species of the Cucurbitaceae, ... more Cucurbita pepo (pumpkin, squash, gourd), an economically important species of the Cucurbitaceae, is extremely variable in fruit characteristics. The objective of the present study was to clarify genetic relationships across a broad spectrum of the C. pepo gene pool, with emphasis on domesticates, using AFLP, ISSR and SSR markers. Forty-five accessions were compared for presence or absence of 448 AFLP, 147 ISSR, and 20 SSR bands, their genetic distances (GDs) were estimated and UPGMA cluster analysis was conducted. The results obtained from these three marker systems were highly correlated (P < 0.001). Clustering was in accordance with the division of C. pepo into three subspecies, fraterna, texana and pepo, with the first two less distant to one another than to the last one. Within the clusters, sub-clustering occurred in accordance with fruit shape and size. The subsp. texana cluster consisted of six sub-clusters, one each for the representatives of its five cultivar-groups (Aco...
Taste has been the subject of human selection in the evolution of agricultural crops, and acidity... more Taste has been the subject of human selection in the evolution of agricultural crops, and acidity is one of the three major components of fleshy fruit taste, together with sugars and volatile flavour compounds. We identify a family of plant-specific genes with a major effect on fruit acidity by map-based cloning of C. melo PH gene (CmPH) from melon, Cucumis melo taking advantage of the novel natural genetic variation for both high and low fruit acidity in this species. Functional silencing of orthologous PH genes in two distantly related plant families, cucumber and tomato, produced low-acid, bland tasting fruit, showing that PH genes control fruit acidity across plant families. A four amino-acid duplication in CmPH distinguishes between primitive acidic varieties and modern dessert melons. This fortuitous mutation served as a preadaptive antecedent to the development of sweet melon cultigens in Central Asia over 1,000 years ago.
This paper is dedicated to Prof. Rodney Croteau in occasion of his 60th birthday, in appreciation... more This paper is dedicated to Prof. Rodney Croteau in occasion of his 60th birthday, in appreciation for his teachings and support.
The availability of sequence information for many plants has opened the way to advanced genetic a... more The availability of sequence information for many plants has opened the way to advanced genetic analysis in many non-model plants. Nevertheless, exploration of genetic variation on a large scale and its use as a tool for the identification of traits of interest are still rare. In this study, we combined a bulk segregation approach with our own-designed microarrays to map the pH locus that influences fruit pH in melon. Using these technologies, we identified a set of markers that are genetically linked to the pH trait. Further analysis using a set of melon cultivars demonstrated that some of these markers are tightly linked to the pH trait throughout our germplasm collection. These results validate the utility of combining microarray technology with a bulk segregation approach in mapping traits of interest in non-model plants.
A composite genetic melon map was generated based on two recombinant inbred line (RI) populations... more A composite genetic melon map was generated based on two recombinant inbred line (RI) populations. By analyzing the segregation of 346 AFLPs, 113 IMAs and phenotypic characters on a RI population of 163 individuals derived from the cross Védrantais × PI 161375, a first map was constructed. About 20% of the molecular markers were skewed, and the residual heterozygosity was estimated at 4.43% which was not significantly different from the theoretical value of 4.2%. The genome distribution of molecular markers among the 12 linkage groups was not different from a random distribution with the exception of linkage group XII which was found significantly less populated. The genome distributions of IMAs and AFLPs were complementary. AFLPs were found mainly in the middle of each linkage group and sometimes clustered, whereas IMAs were found mainly at the end. A total of 318 molecular markers, mainly AFLP and IMA markers, were mapped on 63 RIs of the second population, Védrantais × PI 414723. Comparison of the maps enables one to conclude that AFLPs and IMAs of like molecular size, amplified with the same primer combination, correspond to the same genetic locus. Both maps were joined through 116 common markers comprising 106 comigrating AFLPs/IMAs, plus five SSRs and five phenotypic markers. The integrated melon map contained 668 loci issuing from the segregation of 1,093 molecular markers in the two RI populations. The composite map spanned 1,654 cM on 12 linkage groups which is the haploid number of chromosomes in melon. Thirty two known-function probes, i.e. knownfunction genes (9) and morphological traits (23), were included in this map. In addition, the composite map was anchored to previously published maps through SSRs, RFLPs and phenotypic characters.
We carried out four separate studies using random amplified polymorphic DNA (RAPD) markers to ana... more We carried out four separate studies using random amplified polymorphic DNA (RAPD) markers to analyse samples of Eucalyptus supplied by several different organisations. The objective was to examine the reproducibility of the RAPD technique and its ability to discriminate between individual genotypes for verification of clonal identities. We found that RAPD profiles that are unique to a genotype can be generated reliably and simply and that even closely related genotypes can be distinguished. In addition, in each of the four studies, we detected cases where the plant material studied had been mis-sampled or mis-labelled (i.e. the RAPD profiles were not consistent with the identification numbers): (1) ramets of a Eucalyptus grandis clone were found to be derived from 2 different clones; (2) ramets labelled as 2 different Eucalyptus hybrid clones were found to be the same clone, owing to a mis-planted clonal hedge; (3) samples supplied as a single progeny of a controlled E. nitens cross were derived from two crosses involving different pairs of parents; (4) mis-labelling was detected for ramets of 4 of a set of 10 clones of E. grandis and E. camaldulensis. For three of the four studies, the detection of genotype mis-identifications was unexpected, suggesting that labelling or sampling errors during the handling of plant material are a frequent occurrence, with potentially serious economic consequences.
Sulfur-containing aroma volatiles are important contributors to the distinctive aroma of melon an... more Sulfur-containing aroma volatiles are important contributors to the distinctive aroma of melon and other fruits. Melon cultivars and accessions differ in the content of sulfur-containing and other volatiles. L-methionine has been postulated to serve as a precursor of these volatiles. Incubation of melon fruit cubes with ¹³C- and ²H-labeled L-methionine revealed two distinct catabolic routes into volatiles. One route apparently involves the action of an L-methionine aminotransferase and preserves the main carbon skeleton of L-methionine. The second route apparently involves the action of an L-methionine-γ-lyase activity, releasing methanethiol, a backbone for formation of thiol-derived aroma volatiles. Exogenous L-methionine also generated non-sulfur volatiles by further metabolism of α-ketobutyrate, a product of L-methionine-γ-lyase activity. α-Ketobutyrate was further metabolized into L-isoleucine and other important melon volatiles, including non-sulfur branched and straight-chain esters. Cell-free extracts derived from ripe melon fruit exhibited L-methionine-γ-lyase enzymatic activity. A melon gene (CmMGL) ectopically expressed in Escherichia coli, was shown to encode a protein possessing L-methionine-γ-lyase enzymatic activity. Expression of CmMGL was relatively low in early stages of melon fruit development, but increased in the flesh of ripe fruits, depending on the cultivar tested. Moreover, the levels of expression of CmMGL in recombinant inbred lines co-segregated with the levels of sulfur-containing aroma volatiles enriched with +1 m/z unit and postulated to be produced via this route. Our results indicate that L-methionine is a precursor of both sulfur and non-sulfur aroma volatiles in melon fruit.
Proceedings of the Royal Society B: Biological Sciences, 2012
Bacteria in the genus Rickettsia , best known as vertebrate pathogens vectored by blood-feeding a... more Bacteria in the genus Rickettsia , best known as vertebrate pathogens vectored by blood-feeding arthropods, can also be found in phytophagous insects. The presence of closely related bacterial symbionts in evolutionarily distant arthropod hosts presupposes a means of horizontal transmission, but no mechanism for this transmission has been described. Using a combination of experiments with live insects, molecular analyses and microscopy, we found that Rickettsia were transferred from an insect host (the whitefly Bemisia tabaci ) to a plant, moved inside the phloem, and could be acquired by other whiteflies. In one experiment, Rickettsia was transferred from the whitefly host to leaves of cotton, basil and black nightshade, where the bacteria were restricted to the phloem cells of the plant. In another experiment, Rickettsia -free adult whiteflies, physically segregated but sharing a cotton leaf with Rickettsia -plus individuals, acquired the Rickettsia at a high rate. Plants can serv...
To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv.... more To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv. SR1) mRNA that is up-regulated during senescence was isolated by the cDNA-amplified restriction fragment polymorphism method and the cDNA was cloned. The mRNA coded for the early light-induced protein (ELIP), a member of the chlorophyll a/b-binding protein family that has been implicated in assembly or repair of the photosynthetic machinery during early chloroplast development and abiotic stress. A protein antigenically recognized by antibodies to ELIP appeared during senescence with kinetics similar to those of its mRNA. The mRNA, designated ELIP-TOB, was detected earlier when senescence was enhanced by leaf detachment and treatment with 1-amino-cyclopropane-1-carboxylic acid, and was detected later when senescence was retarded by benzyladenine. However, no ELIP-TOB mRNA was seen in the dark even though senescence was accelerated under these conditions. Furthermore, water stress and anaerobiosis stimulated the appearance of ELIP-TOB mRNA before losses of chlorophyll could be detected. We discuss the conditions that may lead to the up-regulation of ELIP-TOB during senescence and speculate as to the role of the gene product in this terminal phase of leaf development.
Screening of genotypes of melon (Cucumis melo) for resistance to wilt caused by Fusarium oxysporu... more Screening of genotypes of melon (Cucumis melo) for resistance to wilt caused by Fusarium oxysporum f.sp. melonis is often characterized by wide variability in their responses to inoculation, even under carefully controlled conditions. The variability at the seedling stage of 17 genotypes susceptible to race 1 was examined in growth-chamber experiments. Disease incidence varied from 0 to 100% in a genotype-dependent manner. Using four combinations of light (60 and 90 µ E m − 2 s − 1) and temperatures of (27 and 31 ° C), only light intensity showed a statistically significant effect. Markerassisted selection for fusarium resistance breeding using cleaved amplified polymorphic sequence (CAPS) and sequencecharacterized amplified region (SCAR) markers were compared using a single set of genotypes that included 24 melon accessions and breeding lines whose genotype regarding the Fom-2 gene was well characterized. The practical value of the markers for discriminating a range of genotypes and clarifying the scoring of phenotypes was also tested using a segregating breeding population which showed codominant SCAR markers to be useful in marker-assisted selection.
The sweet melon fruit is characterized by a metabolic transition during its development that lead... more The sweet melon fruit is characterized by a metabolic transition during its development that leads to extensive accumulation of the disaccharide sucrose in the mature fruit. While the biochemistry of the sugar metabolism pathway of the cucurbits has been well studied, a comprehensive analysis of the pathway at the transcriptional level allows for a global genomic view of sugar metabolism during fruit sink development. We identified 42 genes encoding the enzymatic reactions of the sugar metabolism pathway in melon. The expression pattern of the 42 genes during fruit development of the sweet melon cv Dulce was determined from a deep sequencing analysis performed by 454 pyrosequencing technology, comprising over 350,000 transcripts from four stages of developing melon fruit flesh, allowing for digital expression of the complete metabolic pathway. The results shed light on the transcriptional control of sugar metabolism in the developing sweet melon fruit, particularly the metabolic transition to sucrose accumulation, and point to a concerted metabolic transition that occurs during fruit development.
A combined chemical, biochemical and molecular study was conducted to understand the differential... more A combined chemical, biochemical and molecular study was conducted to understand the differential accumulation of volatile sesquiterpenes in melon fruits. Sesquiterpenes were present mainly in the rinds of climacteric varieties, and a great diversity in their composition was found among varieties. Sesquiterpenes were generally absent in non-climacteric varieties. Two climacteric melon varieties, the green-fleshed 'Noy Yizre'el', and the orange-fleshed 'Dulce' were further examined. In 'Noy Yizre'el' the main sesquiterpenes accumulated are d-cadinene, c-cadinene and a-copaene, while a-farnesene is the main sesquiterpene in 'Dulce'. Sesquiterpene synthase activities, mainly restricted to rinds of mature fruits, were shown to generate different sesquiterpenes in each variety according to the compositions found in rinds. EST melon database mining yielded two novel cDNAs coding for members of the Tps gene family termed CmTpsNY and CmTpsDul respectively, that are 43.2% similar. Heterologous expression in E. coli of CmTpsNY produced mainly d-copaene, a-copaene, b-caryophyllene, germacrene D, a-muurolene, c-cadinene, d-cadinene, and a-cadinene, while CmTpsDul produced a-farnesene only. CmTpsNY was mostly expressed in 'Noy Yizre'el' rind while CmTpsDul expression was specific to 'Dulce' rind. None of these genes was expressed in rinds of the non-climacteric 'Tam Dew' cultivar. Our results indicate that different sesquiterpene synthases encoded by different members of the Tps gene family are active in melon varieties and this specificity modulates the accumulation of sesquiterpenes. The genes are differentially transcriptionally regulated during fruit development and according to variety and are likely to be associated with chemical differences responsible for the unique aromas of melon varieties.
A normalized cDNA library was constructed using watermelon flesh mRNA from three distinct develop... more A normalized cDNA library was constructed using watermelon flesh mRNA from three distinct developmental time-points and was subtracted by hybridization with leaf cDNA. Random cDNA clones of the watermelon flesh subtraction library were sequenced from the 5 end in order to identify potentially informative genes associated with fruit setting, development, and ripening. One-thousand and forty-six 5-end sequences (expressed sequence tags; ESTs) were assembled into 832 non-redundant sequences, designated as "EST-unigenes". Of these 832 "EST-unigenes", 254 (∼ 30%) have no significant homology to sequences published so far for other plant species. Additionally, 168 "EST-unigenes" (∼ 20%) correspond to genes with unknown function, whereas 410 "EST-unigenes" (∼ 50%) correspond to genes with known function in other plant species. These "EST-unigenes" are
A collection of 351 Verticillium dahliae isolates from cotton, recovered between 1992 and 2000 at... more A collection of 351 Verticillium dahliae isolates from cotton, recovered between 1992 and 2000 at 20 sites in Israel, was tested for vegetative compatibility using nitrate-nonutilizing (nit) mutants. Three cotton-associated vegetative compatibility groups (VCGs) were found ...
Sulfentrazone (F-6285) is a new herbicide, manufactured by FMC, U.S.A. The product is an aryl tri... more Sulfentrazone (F-6285) is a new herbicide, manufactured by FMC, U.S.A. The product is an aryl triazolinone, applied to existing weeds as well as pre-emergence. Sulfentrazone is formulated as 75% w/w water-dispersible granules. It is not volatile, is moderately mobile in the soil, and not sensitive to UV light. It appears to be relatively persistent in the soil; it is decomposed mainly by microbial degradation. Sulfentrazone controls weeds by the same mechanism as the diphenyl ethers, in which membrane disruption is initiated by the inhibition of protoporphyrinogen oxidase in the chlorophyll biosynthetic pathway, which leads to the subsequent buildup of toxic intermediates. Plants emerging from soils treated with sulfentrazone absorb the product through the root system, the weeds turn necrotic and die shortly after exposure to light. When the product is sprayed on existing weeds (foliar application), it is absorbed by the leaves but the movement in the phloem is limited because of rapid foliar desiccation. Sulfentrazone is designed by the manufacturer for the control of weeds in soybeans. In Israel, the product is being tested in various field crops, in orchards and in turf. In field trials it was found to be safe to chickpeas, in pre-emergent application at the rate of 430 g a.i./ha. At this rate, the product prevented emergence of Solanum nigrum, Amaranthus retroflexus, A. blitoides, Polygonum equisetiforme and Cyperus rotundus for the entire chickpea season, without the necessity of manual weeding. At 960 g a.i./ha in preplant application, sulfentrazone was safe to cauliflower and cabbage, and at 1920 g a.i./ha it was safe to citrus seedlings. The product was effective in controlling and preventing emergence of Malva nicaeensis, Senecio vernalis, Urtica urens, Conyza spp. and other winter broadleaved weeds. Winter cereals, including Lolium rigidum, Avena sterihs and wheat, were also controlled by it. Sulfentrazone was sprayed on commercial turf areas after cuttings of the turf carpets. At the rate of 960 g a.i./ha it prevented emergence of Portulaca oleracea, Amaranthus viridis and C. rotundus for a period of more than 90 days after spraying. Sulfentrazone is also being tested in foliar applications on existing turf, for the control of C. rotundus. The characteristics of sulfentrazone, including control of existing weeds, preventing emergence of many widespread winter and summer weeds, long-lasting effect, and its safety to various crops, reveal a good potential for its use in the future.
XXVI International Horticultural Congress: IV International Symposium on Taxonomy of Cultivated Plants, 2004
Cucurbita pepo (pumpkin, squash, gourd) is extremely variable in fruit characteristics. According... more Cucurbita pepo (pumpkin, squash, gourd) is extremely variable in fruit characteristics. According to recent botanical and cultivated-plant taxonomical treatments that were based on variations in allozymes and fruit shape, C. pepo consists of three subspecies containing wild and cultivated, inedible, small-fruited sorts (gourds) and eight groups of edible, large-fruited cultivars (pumpkins and squash). Our objective was to determine if these treatments reflect genetic relationships as viewed at the DNA level, through the use AFLP, ISSR, and SSR markers. Forty-five accessions were compared for presence or absence of 448 AFLP, 147 ISSR, and 20 SSR bands, their genetic distances (GDs) were estimated, and UPGMA cluster analysis was conducted. Correlation coefficients were 0.95 between AFLPs and ISSRs, 0.78 between AFLPs and SSRs, and 0.77 between ISSRs and SSRs, all three comparisons with P << 0.001. Overall, clustering and sub-clustering were much in accordance with two highly polygenic characteristics, fruit shape and size. Clustering occurred in accordance with subspecies and sub-clustering in accordance with cultivar-groups. Within-group GDs were less than corresponding between-group GDs in nearly all comparisons. The smallest-fruited accession, 'Miniature Ball', occupied a central position within C. pepo.
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik, 2003
Cucurbita pepo (pumpkin, squash, gourd), an economically important species of the Cucurbitaceae, ... more Cucurbita pepo (pumpkin, squash, gourd), an economically important species of the Cucurbitaceae, is extremely variable in fruit characteristics. The objective of the present study was to clarify genetic relationships across a broad spectrum of the C. pepo gene pool, with emphasis on domesticates, using AFLP, ISSR and SSR markers. Forty-five accessions were compared for presence or absence of 448 AFLP, 147 ISSR, and 20 SSR bands, their genetic distances (GDs) were estimated and UPGMA cluster analysis was conducted. The results obtained from these three marker systems were highly correlated (P < 0.001). Clustering was in accordance with the division of C. pepo into three subspecies, fraterna, texana and pepo, with the first two less distant to one another than to the last one. Within the clusters, sub-clustering occurred in accordance with fruit shape and size. The subsp. texana cluster consisted of six sub-clusters, one each for the representatives of its five cultivar-groups (Aco...
Taste has been the subject of human selection in the evolution of agricultural crops, and acidity... more Taste has been the subject of human selection in the evolution of agricultural crops, and acidity is one of the three major components of fleshy fruit taste, together with sugars and volatile flavour compounds. We identify a family of plant-specific genes with a major effect on fruit acidity by map-based cloning of C. melo PH gene (CmPH) from melon, Cucumis melo taking advantage of the novel natural genetic variation for both high and low fruit acidity in this species. Functional silencing of orthologous PH genes in two distantly related plant families, cucumber and tomato, produced low-acid, bland tasting fruit, showing that PH genes control fruit acidity across plant families. A four amino-acid duplication in CmPH distinguishes between primitive acidic varieties and modern dessert melons. This fortuitous mutation served as a preadaptive antecedent to the development of sweet melon cultigens in Central Asia over 1,000 years ago.
This paper is dedicated to Prof. Rodney Croteau in occasion of his 60th birthday, in appreciation... more This paper is dedicated to Prof. Rodney Croteau in occasion of his 60th birthday, in appreciation for his teachings and support.
The availability of sequence information for many plants has opened the way to advanced genetic a... more The availability of sequence information for many plants has opened the way to advanced genetic analysis in many non-model plants. Nevertheless, exploration of genetic variation on a large scale and its use as a tool for the identification of traits of interest are still rare. In this study, we combined a bulk segregation approach with our own-designed microarrays to map the pH locus that influences fruit pH in melon. Using these technologies, we identified a set of markers that are genetically linked to the pH trait. Further analysis using a set of melon cultivars demonstrated that some of these markers are tightly linked to the pH trait throughout our germplasm collection. These results validate the utility of combining microarray technology with a bulk segregation approach in mapping traits of interest in non-model plants.
A composite genetic melon map was generated based on two recombinant inbred line (RI) populations... more A composite genetic melon map was generated based on two recombinant inbred line (RI) populations. By analyzing the segregation of 346 AFLPs, 113 IMAs and phenotypic characters on a RI population of 163 individuals derived from the cross Védrantais × PI 161375, a first map was constructed. About 20% of the molecular markers were skewed, and the residual heterozygosity was estimated at 4.43% which was not significantly different from the theoretical value of 4.2%. The genome distribution of molecular markers among the 12 linkage groups was not different from a random distribution with the exception of linkage group XII which was found significantly less populated. The genome distributions of IMAs and AFLPs were complementary. AFLPs were found mainly in the middle of each linkage group and sometimes clustered, whereas IMAs were found mainly at the end. A total of 318 molecular markers, mainly AFLP and IMA markers, were mapped on 63 RIs of the second population, Védrantais × PI 414723. Comparison of the maps enables one to conclude that AFLPs and IMAs of like molecular size, amplified with the same primer combination, correspond to the same genetic locus. Both maps were joined through 116 common markers comprising 106 comigrating AFLPs/IMAs, plus five SSRs and five phenotypic markers. The integrated melon map contained 668 loci issuing from the segregation of 1,093 molecular markers in the two RI populations. The composite map spanned 1,654 cM on 12 linkage groups which is the haploid number of chromosomes in melon. Thirty two known-function probes, i.e. knownfunction genes (9) and morphological traits (23), were included in this map. In addition, the composite map was anchored to previously published maps through SSRs, RFLPs and phenotypic characters.
We carried out four separate studies using random amplified polymorphic DNA (RAPD) markers to ana... more We carried out four separate studies using random amplified polymorphic DNA (RAPD) markers to analyse samples of Eucalyptus supplied by several different organisations. The objective was to examine the reproducibility of the RAPD technique and its ability to discriminate between individual genotypes for verification of clonal identities. We found that RAPD profiles that are unique to a genotype can be generated reliably and simply and that even closely related genotypes can be distinguished. In addition, in each of the four studies, we detected cases where the plant material studied had been mis-sampled or mis-labelled (i.e. the RAPD profiles were not consistent with the identification numbers): (1) ramets of a Eucalyptus grandis clone were found to be derived from 2 different clones; (2) ramets labelled as 2 different Eucalyptus hybrid clones were found to be the same clone, owing to a mis-planted clonal hedge; (3) samples supplied as a single progeny of a controlled E. nitens cross were derived from two crosses involving different pairs of parents; (4) mis-labelling was detected for ramets of 4 of a set of 10 clones of E. grandis and E. camaldulensis. For three of the four studies, the detection of genotype mis-identifications was unexpected, suggesting that labelling or sampling errors during the handling of plant material are a frequent occurrence, with potentially serious economic consequences.
Sulfur-containing aroma volatiles are important contributors to the distinctive aroma of melon an... more Sulfur-containing aroma volatiles are important contributors to the distinctive aroma of melon and other fruits. Melon cultivars and accessions differ in the content of sulfur-containing and other volatiles. L-methionine has been postulated to serve as a precursor of these volatiles. Incubation of melon fruit cubes with ¹³C- and ²H-labeled L-methionine revealed two distinct catabolic routes into volatiles. One route apparently involves the action of an L-methionine aminotransferase and preserves the main carbon skeleton of L-methionine. The second route apparently involves the action of an L-methionine-γ-lyase activity, releasing methanethiol, a backbone for formation of thiol-derived aroma volatiles. Exogenous L-methionine also generated non-sulfur volatiles by further metabolism of α-ketobutyrate, a product of L-methionine-γ-lyase activity. α-Ketobutyrate was further metabolized into L-isoleucine and other important melon volatiles, including non-sulfur branched and straight-chain esters. Cell-free extracts derived from ripe melon fruit exhibited L-methionine-γ-lyase enzymatic activity. A melon gene (CmMGL) ectopically expressed in Escherichia coli, was shown to encode a protein possessing L-methionine-γ-lyase enzymatic activity. Expression of CmMGL was relatively low in early stages of melon fruit development, but increased in the flesh of ripe fruits, depending on the cultivar tested. Moreover, the levels of expression of CmMGL in recombinant inbred lines co-segregated with the levels of sulfur-containing aroma volatiles enriched with +1 m/z unit and postulated to be produced via this route. Our results indicate that L-methionine is a precursor of both sulfur and non-sulfur aroma volatiles in melon fruit.
Proceedings of the Royal Society B: Biological Sciences, 2012
Bacteria in the genus Rickettsia , best known as vertebrate pathogens vectored by blood-feeding a... more Bacteria in the genus Rickettsia , best known as vertebrate pathogens vectored by blood-feeding arthropods, can also be found in phytophagous insects. The presence of closely related bacterial symbionts in evolutionarily distant arthropod hosts presupposes a means of horizontal transmission, but no mechanism for this transmission has been described. Using a combination of experiments with live insects, molecular analyses and microscopy, we found that Rickettsia were transferred from an insect host (the whitefly Bemisia tabaci ) to a plant, moved inside the phloem, and could be acquired by other whiteflies. In one experiment, Rickettsia was transferred from the whitefly host to leaves of cotton, basil and black nightshade, where the bacteria were restricted to the phloem cells of the plant. In another experiment, Rickettsia -free adult whiteflies, physically segregated but sharing a cotton leaf with Rickettsia -plus individuals, acquired the Rickettsia at a high rate. Plants can serv...
To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv.... more To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv. SR1) mRNA that is up-regulated during senescence was isolated by the cDNA-amplified restriction fragment polymorphism method and the cDNA was cloned. The mRNA coded for the early light-induced protein (ELIP), a member of the chlorophyll a/b-binding protein family that has been implicated in assembly or repair of the photosynthetic machinery during early chloroplast development and abiotic stress. A protein antigenically recognized by antibodies to ELIP appeared during senescence with kinetics similar to those of its mRNA. The mRNA, designated ELIP-TOB, was detected earlier when senescence was enhanced by leaf detachment and treatment with 1-amino-cyclopropane-1-carboxylic acid, and was detected later when senescence was retarded by benzyladenine. However, no ELIP-TOB mRNA was seen in the dark even though senescence was accelerated under these conditions. Furthermore, water stress and anaerobiosis stimulated the appearance of ELIP-TOB mRNA before losses of chlorophyll could be detected. We discuss the conditions that may lead to the up-regulation of ELIP-TOB during senescence and speculate as to the role of the gene product in this terminal phase of leaf development.
Screening of genotypes of melon (Cucumis melo) for resistance to wilt caused by Fusarium oxysporu... more Screening of genotypes of melon (Cucumis melo) for resistance to wilt caused by Fusarium oxysporum f.sp. melonis is often characterized by wide variability in their responses to inoculation, even under carefully controlled conditions. The variability at the seedling stage of 17 genotypes susceptible to race 1 was examined in growth-chamber experiments. Disease incidence varied from 0 to 100% in a genotype-dependent manner. Using four combinations of light (60 and 90 µ E m − 2 s − 1) and temperatures of (27 and 31 ° C), only light intensity showed a statistically significant effect. Markerassisted selection for fusarium resistance breeding using cleaved amplified polymorphic sequence (CAPS) and sequencecharacterized amplified region (SCAR) markers were compared using a single set of genotypes that included 24 melon accessions and breeding lines whose genotype regarding the Fom-2 gene was well characterized. The practical value of the markers for discriminating a range of genotypes and clarifying the scoring of phenotypes was also tested using a segregating breeding population which showed codominant SCAR markers to be useful in marker-assisted selection.
The sweet melon fruit is characterized by a metabolic transition during its development that lead... more The sweet melon fruit is characterized by a metabolic transition during its development that leads to extensive accumulation of the disaccharide sucrose in the mature fruit. While the biochemistry of the sugar metabolism pathway of the cucurbits has been well studied, a comprehensive analysis of the pathway at the transcriptional level allows for a global genomic view of sugar metabolism during fruit sink development. We identified 42 genes encoding the enzymatic reactions of the sugar metabolism pathway in melon. The expression pattern of the 42 genes during fruit development of the sweet melon cv Dulce was determined from a deep sequencing analysis performed by 454 pyrosequencing technology, comprising over 350,000 transcripts from four stages of developing melon fruit flesh, allowing for digital expression of the complete metabolic pathway. The results shed light on the transcriptional control of sugar metabolism in the developing sweet melon fruit, particularly the metabolic transition to sucrose accumulation, and point to a concerted metabolic transition that occurs during fruit development.
A combined chemical, biochemical and molecular study was conducted to understand the differential... more A combined chemical, biochemical and molecular study was conducted to understand the differential accumulation of volatile sesquiterpenes in melon fruits. Sesquiterpenes were present mainly in the rinds of climacteric varieties, and a great diversity in their composition was found among varieties. Sesquiterpenes were generally absent in non-climacteric varieties. Two climacteric melon varieties, the green-fleshed 'Noy Yizre'el', and the orange-fleshed 'Dulce' were further examined. In 'Noy Yizre'el' the main sesquiterpenes accumulated are d-cadinene, c-cadinene and a-copaene, while a-farnesene is the main sesquiterpene in 'Dulce'. Sesquiterpene synthase activities, mainly restricted to rinds of mature fruits, were shown to generate different sesquiterpenes in each variety according to the compositions found in rinds. EST melon database mining yielded two novel cDNAs coding for members of the Tps gene family termed CmTpsNY and CmTpsDul respectively, that are 43.2% similar. Heterologous expression in E. coli of CmTpsNY produced mainly d-copaene, a-copaene, b-caryophyllene, germacrene D, a-muurolene, c-cadinene, d-cadinene, and a-cadinene, while CmTpsDul produced a-farnesene only. CmTpsNY was mostly expressed in 'Noy Yizre'el' rind while CmTpsDul expression was specific to 'Dulce' rind. None of these genes was expressed in rinds of the non-climacteric 'Tam Dew' cultivar. Our results indicate that different sesquiterpene synthases encoded by different members of the Tps gene family are active in melon varieties and this specificity modulates the accumulation of sesquiterpenes. The genes are differentially transcriptionally regulated during fruit development and according to variety and are likely to be associated with chemical differences responsible for the unique aromas of melon varieties.
A normalized cDNA library was constructed using watermelon flesh mRNA from three distinct develop... more A normalized cDNA library was constructed using watermelon flesh mRNA from three distinct developmental time-points and was subtracted by hybridization with leaf cDNA. Random cDNA clones of the watermelon flesh subtraction library were sequenced from the 5 end in order to identify potentially informative genes associated with fruit setting, development, and ripening. One-thousand and forty-six 5-end sequences (expressed sequence tags; ESTs) were assembled into 832 non-redundant sequences, designated as "EST-unigenes". Of these 832 "EST-unigenes", 254 (∼ 30%) have no significant homology to sequences published so far for other plant species. Additionally, 168 "EST-unigenes" (∼ 20%) correspond to genes with unknown function, whereas 410 "EST-unigenes" (∼ 50%) correspond to genes with known function in other plant species. These "EST-unigenes" are
A collection of 351 Verticillium dahliae isolates from cotton, recovered between 1992 and 2000 at... more A collection of 351 Verticillium dahliae isolates from cotton, recovered between 1992 and 2000 at 20 sites in Israel, was tested for vegetative compatibility using nitrate-nonutilizing (nit) mutants. Three cotton-associated vegetative compatibility groups (VCGs) were found ...
Sulfentrazone (F-6285) is a new herbicide, manufactured by FMC, U.S.A. The product is an aryl tri... more Sulfentrazone (F-6285) is a new herbicide, manufactured by FMC, U.S.A. The product is an aryl triazolinone, applied to existing weeds as well as pre-emergence. Sulfentrazone is formulated as 75% w/w water-dispersible granules. It is not volatile, is moderately mobile in the soil, and not sensitive to UV light. It appears to be relatively persistent in the soil; it is decomposed mainly by microbial degradation. Sulfentrazone controls weeds by the same mechanism as the diphenyl ethers, in which membrane disruption is initiated by the inhibition of protoporphyrinogen oxidase in the chlorophyll biosynthetic pathway, which leads to the subsequent buildup of toxic intermediates. Plants emerging from soils treated with sulfentrazone absorb the product through the root system, the weeds turn necrotic and die shortly after exposure to light. When the product is sprayed on existing weeds (foliar application), it is absorbed by the leaves but the movement in the phloem is limited because of rapid foliar desiccation. Sulfentrazone is designed by the manufacturer for the control of weeds in soybeans. In Israel, the product is being tested in various field crops, in orchards and in turf. In field trials it was found to be safe to chickpeas, in pre-emergent application at the rate of 430 g a.i./ha. At this rate, the product prevented emergence of Solanum nigrum, Amaranthus retroflexus, A. blitoides, Polygonum equisetiforme and Cyperus rotundus for the entire chickpea season, without the necessity of manual weeding. At 960 g a.i./ha in preplant application, sulfentrazone was safe to cauliflower and cabbage, and at 1920 g a.i./ha it was safe to citrus seedlings. The product was effective in controlling and preventing emergence of Malva nicaeensis, Senecio vernalis, Urtica urens, Conyza spp. and other winter broadleaved weeds. Winter cereals, including Lolium rigidum, Avena sterihs and wheat, were also controlled by it. Sulfentrazone was sprayed on commercial turf areas after cuttings of the turf carpets. At the rate of 960 g a.i./ha it prevented emergence of Portulaca oleracea, Amaranthus viridis and C. rotundus for a period of more than 90 days after spraying. Sulfentrazone is also being tested in foliar applications on existing turf, for the control of C. rotundus. The characteristics of sulfentrazone, including control of existing weeds, preventing emergence of many widespread winter and summer weeds, long-lasting effect, and its safety to various crops, reveal a good potential for its use in the future.
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