The brassinosteroid (BR) hormone and its plasma membrane (PM) receptor BR INSENSITIVE1 (BRI1) are... more The brassinosteroid (BR) hormone and its plasma membrane (PM) receptor BR INSENSITIVE1 (BRI1) are one of the best-studied receptor–ligand pairs for understanding the interplay between receptor endocytosis and signaling in plants. BR signaling is mainly determined by the PM pool of BRI1, whereas BRI1 endocytosis ensures signal attenuation. As BRs are ubiquitously distributed in the plant, the tools available to study the BRI1 function without interference from endogenous BRs are limited. Here, we designed a BR binding-deficient Arabidopsis (Arabidopsis thaliana) mutant based on protein sequence-structure analysis and homology modeling of members of the BRI1 family. This tool allowed us to re-examine the BRI1 endocytosis and signal attenuation model. We showed that despite impaired phosphorylation and ubiquitination, BR binding-deficient BRI1 internalizes similarly to the wild type form. Our data indicate that BRI1 internalization relies on different endocytic machineries. In addition...
Plants have evolved both cell surface-resident receptor-like kinases (RLKs) and intracellular nuc... more Plants have evolved both cell surface-resident receptor-like kinases (RLKs) and intracellular nucleotide-binding leucine-rich repeat (NLR) proteins as immune receptors to detect infections. It remains enigmatic how RLK-and NLR-mediated signaling is connected. Disruption of an immune-activated MEKK1-MKK1/2-MPK4 MAPK cascade activates the NLR SUMM2 via the MAPK kinase kinase MEKK2, leading to autoimmunity. To gain insights into the mechanisms underlying SUMM2 activation, we deployed an RNAi-based genetic screen for mekk1 autoimmune suppressors, and identified an uncharacterized malectin-like RLK, named LETUM1 (LET1), as a specific regulator of mekk1-mkk1/2-mpk4 autoimmunity via complexing with both SUMM2 and MEKK2. MEKK2 scaffolds LET1 and SUMM2 for protein stability and association, and counter-regulates the F-box protein CPR1-mediated SUMM2 ubiquitination and degradation; thereby, regulating SUMM2 accumulation and activation. Our study indicates that malectin-like Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
Sugar allocation between vegetative and reproductive tissues is vital to plant development, and s... more Sugar allocation between vegetative and reproductive tissues is vital to plant development, and sugar transporters play fundamental roles in this process. Although several transcription factors have been identified that control their transcription levels, the way in which the expression of sugar transporter genes is controlled at the posttranscriptional level is unknown. In this study, we showed that OsRRM, an RNA-binding protein, modulates sugar allocation in tissues on the source-to-sink route. The OsRRM expression pattern partly resembles that of several sugar transporter and transcription factor genes that specifically affect sugar transporter gene expression. The messenger RNA levels of almost all of the sugar transporter genes are severely reduced in the osrrm mutant, and this alters sugar metabolism and sugar signaling, which further affects plant height, flowering time, seed size, and starch synthesis. We further showed that OsRRM binds directly to messenger RNAs encoded by ...
The rice Waxy (Wx) gene encodes granule-bound starch synthase 1 (EC 2.4.1.242), OsGBSS1, which is... more The rice Waxy (Wx) gene encodes granule-bound starch synthase 1 (EC 2.4.1.242), OsGBSS1, which is responsible for amylose synthesis in rice seed endosperm. In this study, we determined the functional contribution of eight amino acids on the activity of OsGBSS1 by introducing site-directed mutated Wx gene constructs into the wx mutant glutinous rice. The eight amino acid residues are suspected to play roles in OsGBSS1 structure maintenance or function based on homologous enzyme sequence alignment and homology modelling. Both OsGBSS1 activity and amylose content were analysed in homozygous transgenic lines carrying the mutated OsGBSS1 (Wx) genes. Our results indicate that mutations at diverse sites in OsGBSS1 reduces its activity by affecting its starch-binding capacity, its ADP-glucose-binding capability or its protein stability. Our results shed new light on the structural basis of OsGBSS1 activity and the mechanisms of OsGBSS1 activity on amylose synthesis in vivo. This study also ...
Granule-bound starch synthase 1 (GBSS1) is responsible for amylose synthesis in cereals, and this... more Granule-bound starch synthase 1 (GBSS1) is responsible for amylose synthesis in cereals, and this enzyme is regulated at the transcriptional and post-transcriptional levels. In this study, we show that GBSS1 from Oryza sativa L. (OsGBSS1) can form oligomers in rice endosperm, and oligomerized OsGBSS1 exhibits much higher specific enzymatic activity than the monomer. A monomer-oligomer transition equilibrium for OsGBSS1 occurs in the endosperm during development. Redox potential is a key factor affecting the oligomer percentage as well as the enzymatic activity of OsGBSS1. Adenosine diphosphate glucose, the direct donor of glucose, also impacts OsGBSS1 oligomerization in a concentration-dependent manner. OsGBSS1 oligomerization is influenced by phosphorylation status, which was strongly enhanced by Mitogen-activated protein kinase (MAPK) and ATP treatment and was sharply weakened by protein phosphatase (PPase) treatment. The activity of OsGBSS1 affects the ratio of amylose to amylopectin and therefore the eating quality of rice. Understanding the regulation of OsGBSS1 activity may lead to the improvement of rice eating quality.
OsRRMh, a homologue of OsRRM, encodes a Spen-like protein, and is composed of two N-terminal RNA ... more OsRRMh, a homologue of OsRRM, encodes a Spen-like protein, and is composed of two N-terminal RNA recognition motifs (RRM) and one C-terminal Spen paralogue and an orthologue C-terminal domain (SPOC). The gene has been found to be constitutively expressed in the root, stem, leaf, spikelet, and immature seed, and alternative splicing patterns were confirmed in different tissues, which may indicate diverse functions for OsRRMh. The OsRRMh dsRNAi lines exhibited late-flowering and a larger panicle phenotype. When full-length OsRRMh and/or its SPOC domain were overexpressed, the fertility rate and number of spikelets per panicle were both markedly reduced. Also, overexpression of OsRRMh in the Arabidopsis fpa mutant did not restore the normal flowering time, and it delayed flowering in Col plants. Therefore, we propose that OsRRMh may confer one of its functions in the vegetative-to-reproductive transition in rice (Oryza sativa L. subsp. japonica cv. Zhonghua No. 11 (ZH11)).
The brassinosteroid (BR) hormone and its plasma membrane receptor BR INSENSITIVE1 (BRI1) is one o... more The brassinosteroid (BR) hormone and its plasma membrane receptor BR INSENSITIVE1 (BRI1) is one of the best-studied receptor-ligand pairs for understanding the interplay between receptor endocytosis and signaling in plants. BR signaling is mainly determined by the plasma membrane pool of BRI1, whereas BRI1 endocytosis ensures signal attenuation. Since BRs are ubiquitously distributed in the plant, the tools available to study BRI1 function without interference from endogenous BRs are limited. Here, we designed a BR-binding-deficient mutant based on protein sequence-structure analysis and homology modeling of BRI1 and its close homologues. This new tool allowed us to re-examine the BRI1 endocytosis and signal attenuation model. We show that despite decreased phosphorylation and ubiquitination, the BR-binding-deficient BRI1 was internalized similar to the wild type form. These results reinforce the hypothesis that BRI1 is internalized via parallel endocytic routes and machineries. In ...
Plant plasma membrane-resident immune receptors regulate plant immunity by recognizing microbe-as... more Plant plasma membrane-resident immune receptors regulate plant immunity by recognizing microbe-associated molecular patterns (MAMPs), damage-associated molecular patterns (DAMPs), and phytocytokines. Phytocytokines are plant endogenous peptides, which are usually produced in the cytosol and released into the apoplast when plant encounters pathogen infections. Phytocytokines regulate plant immunity through activating an overlapping signaling pathway with MAMPs/DAMPs with some unique features. Here, we highlight the current understanding of phytocytokine production, perception and functions in plant immunity, and discuss how plants and pathogens manipulate phytocytokine signaling for their own benefits during the plant-pathogen warfare.
Sessile plants encode a large number of small peptides and cell surface-resident receptor kinases... more Sessile plants encode a large number of small peptides and cell surface-resident receptor kinases, most of which have unknown functions. Here, we report that the Arabidopsis receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) recognizes the conserved signature motif of SERINE-RICH ENDOGENOUS PEPTIDEs (SCOOPs) from Brassicaceae plants as well as proteins present in fungal Fusarium spp. and bacterial Comamonadaceae, and elicits various immune responses. SCOOP signature peptides trigger immune responses and altered root development in a MIK2-dependent manner with a sub-nanomolar sensitivity. SCOOP12 directly binds to the extracellular leucine-rich repeat domain of MIK2 in vivo and in vitro, indicating that MIK2 is the receptor of SCOOP peptides. Perception of SCOOP peptides induces the association of MIK2 and the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3 (SERK3) and SERK4 and relays the signaling through the cytosolic receptor-like kinases BOTRYTIS-IND...
ABSTRACTSessile plants encode a large number of small peptides and cell surface-resident receptor... more ABSTRACTSessile plants encode a large number of small peptides and cell surface-resident receptor kinases, most of which have unknown functions. Here, we report that the Arabidopsis receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) recognizes the conserved signature motif of SERINE RICH ENDOGENOUS PEPTIDEs (SCOOPs) from plants as well as proteins present in fungal Fusarium spp. and bacterial Comamonadaceae, and elicits potent immune responses. SCOOP signature peptides trigger diverse immune and physiological responses in a MIK2-dependent manner with a sub-nanomolar sensitivity and directly bind to the extracellular leucine rich-repeat domain of MIK2 in vivo and in vitro, indicating that MIK2 is the receptor of SCOOP peptides. Perception of SCOOP peptides induces the association of MIK2 and the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3 (SERK3) and SERK4 and relays the signaling through the cytosolic receptor-like kinases BOTRYTIS-INDUCED KINASE 1 (...
Clathrin-mediated endocytosis (CME) and its core endocytic machinery are evolutionarily conserved... more Clathrin-mediated endocytosis (CME) and its core endocytic machinery are evolutionarily conserved across all eukaryotes. In mammals, the heterotetrameric adaptor protein complex-2 (AP-2) sorts plasma membrane (PM) cargoes into vesicles via the recognition of motifs based on Tyr or di-Leu in their cytoplasmic tails. However, in plants, very little is known about how PM proteins are sorted for CME and whether similar motifs are required. In Arabidopsis (Arabidopsis thaliana), the brassinosteroid (BR) receptor BR INSENSITIVE1 (BRI1) undergoes endocytosis, which depends on clathrin and AP-2. Here, we demonstrate that BRI1 binds directly to the medium AP-2 subunit (AP2M). The cytoplasmic domain of BRI1 contains five putative canonical surface-exposed Tyr-based endocytic motifs. The Tyr-to-Phe substitution in Y898KAI reduced BRI1 internalization without affecting its kinase activity. Consistently, plants carrying the BRI1Y898F mutation were hypersensitive to BRs. Our study demonstrates th...
Brassinosteroids (BRs) are a group of polyhydroxylated plant steroid hormones that are crucial fo... more Brassinosteroids (BRs) are a group of polyhydroxylated plant steroid hormones that are crucial for many aspects of a plant's life. BRs were originally characterized for their function in cell elongation, but it is becoming clear that they play major roles in plant growth, development, and responses to several stresses such as extreme temperatures and drought. A BR signaling pathway from cell surface receptors to central transcription factors has been well characterized. Here, we summarize recent progress toward understanding the BR pathway, including BR perception and the molecular mechanisms of BR signaling. Next, we discuss the roles of BRs in development and stress responses. Finally, we show how knowledge of the BR pathway is being applied to manipulate the growth and stress responses of crops. These studies highlight the complex regulation of BR signaling, multiple points of crosstalk between BRs and other hormones or stress responses, and the finely tuned spatiotemporal regulation of BR signaling.
Soil microbial communities hold great potential for sustainable and ecologically compatible agric... more Soil microbial communities hold great potential for sustainable and ecologically compatible agriculture. Although numerous plant-beneficial bacterial strains from a wide range of taxonomic groups have been reported, very little evidence is available on the plant-beneficial role of bacteria from the genus Caulobacter. Here, the mode of action of a Caulobacter strain, designated RHG1, which had originally been identified through a microbial screen for plant growth-promoting (PGP) bacteria in maize (Zea mays), is investigated in Arabidopsis thaliana. RHG1 colonized both roots and shoots of Arabidopsis, promoted lateral root formation in the root, and increased leaf number and leaf size in the shoot. The genome of RHG1 was sequenced and was utilized to look for PGP factors. Our data revealed that the bacterial production of nitric oxide, auxins, cytokinins, or 1-aminocyclopropane-1-carboxylate deaminase as PGP factors could be excluded. However, the analysis of brassinosteroid mutants s...
Proceedings of the National Academy of Sciences of the United States of America, Feb 5, 2018
Plants largely rely on plasma membrane (PM)-resident receptor-like kinases (RLKs) to sense extrac... more Plants largely rely on plasma membrane (PM)-resident receptor-like kinases (RLKs) to sense extracellular and intracellular stimuli and coordinate cell differentiation, growth, and immunity. Several RLKs have been shown to undergo internalization through the endocytic pathway with a poorly understood mechanism. Here, we show that endocytosis and protein abundance of thebrassinosteroid (BR) receptor, BR INSENSITIVE1 (BRI1), are regulated by plant U-box (PUB) E3 ubiquitin ligase PUB12- and PUB13-mediated ubiquitination. BR perception promotes BRI1 ubiquitination and association with PUB12 and PUB13 through phosphorylation at serine 344 residue. Loss of PUB12 and PUB13 results in reduced BRI1 ubiquitination and internalization accompanied with a prolonged BRI1 PM-residence time, indicating that ubiquitination of BRI1 by PUB12 and PUB13 is a key step in BRI1 endocytosis. Our studies provide a molecular link between BRI1 ubiquitination and internalization and reveal a unique mechanism of ...
The mechanism of cellulose synthesis has been studied by characterizing the motility of cellulose... more The mechanism of cellulose synthesis has been studied by characterizing the motility of cellulose synthase complexes tagged with a fluorescent protein; however, this approach has been used exclusively on the hypocotyl of Arabidopsis thaliana. Here we characterize cellulose synthase motility in the model grass, Brachypodium distachyon. We generated lines in which mEGFP is fused N-terminal to BdCESA3 or BdCESA6 and which grew indistinguishably from the wild type (Bd21-3) and had dense fluorescent puncta at or near the plasma membrane. Measured with a particle tracking algorithm, the average speed of GFP-BdCESA3 particles in the mesocotyl was 164 ± 78 nm min(-1) (error gives standard deviation [SD], n = 1451 particles). Mean speed in the root appeared similar. For comparison, average speed in the A. thaliana hypocotyl expressing GFP-AtCESA6 was 184 ± 86 nm min(-1) (n = 2755). For B. distachyon, we quantified root diameter and elongation rate in response to inhibitors of cellulose (dich...
The polysaccharide cellulose is the main component of plant cell walls, so it is the most abundan... more The polysaccharide cellulose is the main component of plant cell walls, so it is the most abundant polymer on the earth. While it is widely used in industry due to its remarkable properties, such as renewability and biodegradability, its biosynthesis is still not well understood. The large transmembrane protein complex responsible for synthesizing cellulose contains several cellulose synthase A (CESA) subunits that polymerize UDP glucose into the constituent glucan chains of cellulose. Here, we used variable angle epi-fluorescence microscopy in combination with single-particle tracking to characterize the motion of GFP labeled CESA complexes in the root and mesocotyl of Brachypodium distachyon seedlings that are a 3 to 4 days old. We show that CESA complexes move through the plasma membrane at approximately 165 nm/minute. Their motion is known to be guided by cortical microtubules, but no molecular motors are involved. Rather, the motion is thought to be driven by the polymerization and crystallization of the cellulose. A mean-squared displacement analysis shows that CESA complexes move diffusively on short time scales and undergo a transition to super-diffusive motion on a time scale of about 10 s. We also report on the effect of actin and microtubule inhibitors on CESA motion.
The brassinosteroid (BR) hormone and its plasma membrane (PM) receptor BR INSENSITIVE1 (BRI1) are... more The brassinosteroid (BR) hormone and its plasma membrane (PM) receptor BR INSENSITIVE1 (BRI1) are one of the best-studied receptor–ligand pairs for understanding the interplay between receptor endocytosis and signaling in plants. BR signaling is mainly determined by the PM pool of BRI1, whereas BRI1 endocytosis ensures signal attenuation. As BRs are ubiquitously distributed in the plant, the tools available to study the BRI1 function without interference from endogenous BRs are limited. Here, we designed a BR binding-deficient Arabidopsis (Arabidopsis thaliana) mutant based on protein sequence-structure analysis and homology modeling of members of the BRI1 family. This tool allowed us to re-examine the BRI1 endocytosis and signal attenuation model. We showed that despite impaired phosphorylation and ubiquitination, BR binding-deficient BRI1 internalizes similarly to the wild type form. Our data indicate that BRI1 internalization relies on different endocytic machineries. In addition...
Plants have evolved both cell surface-resident receptor-like kinases (RLKs) and intracellular nuc... more Plants have evolved both cell surface-resident receptor-like kinases (RLKs) and intracellular nucleotide-binding leucine-rich repeat (NLR) proteins as immune receptors to detect infections. It remains enigmatic how RLK-and NLR-mediated signaling is connected. Disruption of an immune-activated MEKK1-MKK1/2-MPK4 MAPK cascade activates the NLR SUMM2 via the MAPK kinase kinase MEKK2, leading to autoimmunity. To gain insights into the mechanisms underlying SUMM2 activation, we deployed an RNAi-based genetic screen for mekk1 autoimmune suppressors, and identified an uncharacterized malectin-like RLK, named LETUM1 (LET1), as a specific regulator of mekk1-mkk1/2-mpk4 autoimmunity via complexing with both SUMM2 and MEKK2. MEKK2 scaffolds LET1 and SUMM2 for protein stability and association, and counter-regulates the F-box protein CPR1-mediated SUMM2 ubiquitination and degradation; thereby, regulating SUMM2 accumulation and activation. Our study indicates that malectin-like Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
Sugar allocation between vegetative and reproductive tissues is vital to plant development, and s... more Sugar allocation between vegetative and reproductive tissues is vital to plant development, and sugar transporters play fundamental roles in this process. Although several transcription factors have been identified that control their transcription levels, the way in which the expression of sugar transporter genes is controlled at the posttranscriptional level is unknown. In this study, we showed that OsRRM, an RNA-binding protein, modulates sugar allocation in tissues on the source-to-sink route. The OsRRM expression pattern partly resembles that of several sugar transporter and transcription factor genes that specifically affect sugar transporter gene expression. The messenger RNA levels of almost all of the sugar transporter genes are severely reduced in the osrrm mutant, and this alters sugar metabolism and sugar signaling, which further affects plant height, flowering time, seed size, and starch synthesis. We further showed that OsRRM binds directly to messenger RNAs encoded by ...
The rice Waxy (Wx) gene encodes granule-bound starch synthase 1 (EC 2.4.1.242), OsGBSS1, which is... more The rice Waxy (Wx) gene encodes granule-bound starch synthase 1 (EC 2.4.1.242), OsGBSS1, which is responsible for amylose synthesis in rice seed endosperm. In this study, we determined the functional contribution of eight amino acids on the activity of OsGBSS1 by introducing site-directed mutated Wx gene constructs into the wx mutant glutinous rice. The eight amino acid residues are suspected to play roles in OsGBSS1 structure maintenance or function based on homologous enzyme sequence alignment and homology modelling. Both OsGBSS1 activity and amylose content were analysed in homozygous transgenic lines carrying the mutated OsGBSS1 (Wx) genes. Our results indicate that mutations at diverse sites in OsGBSS1 reduces its activity by affecting its starch-binding capacity, its ADP-glucose-binding capability or its protein stability. Our results shed new light on the structural basis of OsGBSS1 activity and the mechanisms of OsGBSS1 activity on amylose synthesis in vivo. This study also ...
Granule-bound starch synthase 1 (GBSS1) is responsible for amylose synthesis in cereals, and this... more Granule-bound starch synthase 1 (GBSS1) is responsible for amylose synthesis in cereals, and this enzyme is regulated at the transcriptional and post-transcriptional levels. In this study, we show that GBSS1 from Oryza sativa L. (OsGBSS1) can form oligomers in rice endosperm, and oligomerized OsGBSS1 exhibits much higher specific enzymatic activity than the monomer. A monomer-oligomer transition equilibrium for OsGBSS1 occurs in the endosperm during development. Redox potential is a key factor affecting the oligomer percentage as well as the enzymatic activity of OsGBSS1. Adenosine diphosphate glucose, the direct donor of glucose, also impacts OsGBSS1 oligomerization in a concentration-dependent manner. OsGBSS1 oligomerization is influenced by phosphorylation status, which was strongly enhanced by Mitogen-activated protein kinase (MAPK) and ATP treatment and was sharply weakened by protein phosphatase (PPase) treatment. The activity of OsGBSS1 affects the ratio of amylose to amylopectin and therefore the eating quality of rice. Understanding the regulation of OsGBSS1 activity may lead to the improvement of rice eating quality.
OsRRMh, a homologue of OsRRM, encodes a Spen-like protein, and is composed of two N-terminal RNA ... more OsRRMh, a homologue of OsRRM, encodes a Spen-like protein, and is composed of two N-terminal RNA recognition motifs (RRM) and one C-terminal Spen paralogue and an orthologue C-terminal domain (SPOC). The gene has been found to be constitutively expressed in the root, stem, leaf, spikelet, and immature seed, and alternative splicing patterns were confirmed in different tissues, which may indicate diverse functions for OsRRMh. The OsRRMh dsRNAi lines exhibited late-flowering and a larger panicle phenotype. When full-length OsRRMh and/or its SPOC domain were overexpressed, the fertility rate and number of spikelets per panicle were both markedly reduced. Also, overexpression of OsRRMh in the Arabidopsis fpa mutant did not restore the normal flowering time, and it delayed flowering in Col plants. Therefore, we propose that OsRRMh may confer one of its functions in the vegetative-to-reproductive transition in rice (Oryza sativa L. subsp. japonica cv. Zhonghua No. 11 (ZH11)).
The brassinosteroid (BR) hormone and its plasma membrane receptor BR INSENSITIVE1 (BRI1) is one o... more The brassinosteroid (BR) hormone and its plasma membrane receptor BR INSENSITIVE1 (BRI1) is one of the best-studied receptor-ligand pairs for understanding the interplay between receptor endocytosis and signaling in plants. BR signaling is mainly determined by the plasma membrane pool of BRI1, whereas BRI1 endocytosis ensures signal attenuation. Since BRs are ubiquitously distributed in the plant, the tools available to study BRI1 function without interference from endogenous BRs are limited. Here, we designed a BR-binding-deficient mutant based on protein sequence-structure analysis and homology modeling of BRI1 and its close homologues. This new tool allowed us to re-examine the BRI1 endocytosis and signal attenuation model. We show that despite decreased phosphorylation and ubiquitination, the BR-binding-deficient BRI1 was internalized similar to the wild type form. These results reinforce the hypothesis that BRI1 is internalized via parallel endocytic routes and machineries. In ...
Plant plasma membrane-resident immune receptors regulate plant immunity by recognizing microbe-as... more Plant plasma membrane-resident immune receptors regulate plant immunity by recognizing microbe-associated molecular patterns (MAMPs), damage-associated molecular patterns (DAMPs), and phytocytokines. Phytocytokines are plant endogenous peptides, which are usually produced in the cytosol and released into the apoplast when plant encounters pathogen infections. Phytocytokines regulate plant immunity through activating an overlapping signaling pathway with MAMPs/DAMPs with some unique features. Here, we highlight the current understanding of phytocytokine production, perception and functions in plant immunity, and discuss how plants and pathogens manipulate phytocytokine signaling for their own benefits during the plant-pathogen warfare.
Sessile plants encode a large number of small peptides and cell surface-resident receptor kinases... more Sessile plants encode a large number of small peptides and cell surface-resident receptor kinases, most of which have unknown functions. Here, we report that the Arabidopsis receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) recognizes the conserved signature motif of SERINE-RICH ENDOGENOUS PEPTIDEs (SCOOPs) from Brassicaceae plants as well as proteins present in fungal Fusarium spp. and bacterial Comamonadaceae, and elicits various immune responses. SCOOP signature peptides trigger immune responses and altered root development in a MIK2-dependent manner with a sub-nanomolar sensitivity. SCOOP12 directly binds to the extracellular leucine-rich repeat domain of MIK2 in vivo and in vitro, indicating that MIK2 is the receptor of SCOOP peptides. Perception of SCOOP peptides induces the association of MIK2 and the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3 (SERK3) and SERK4 and relays the signaling through the cytosolic receptor-like kinases BOTRYTIS-IND...
ABSTRACTSessile plants encode a large number of small peptides and cell surface-resident receptor... more ABSTRACTSessile plants encode a large number of small peptides and cell surface-resident receptor kinases, most of which have unknown functions. Here, we report that the Arabidopsis receptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) recognizes the conserved signature motif of SERINE RICH ENDOGENOUS PEPTIDEs (SCOOPs) from plants as well as proteins present in fungal Fusarium spp. and bacterial Comamonadaceae, and elicits potent immune responses. SCOOP signature peptides trigger diverse immune and physiological responses in a MIK2-dependent manner with a sub-nanomolar sensitivity and directly bind to the extracellular leucine rich-repeat domain of MIK2 in vivo and in vitro, indicating that MIK2 is the receptor of SCOOP peptides. Perception of SCOOP peptides induces the association of MIK2 and the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3 (SERK3) and SERK4 and relays the signaling through the cytosolic receptor-like kinases BOTRYTIS-INDUCED KINASE 1 (...
Clathrin-mediated endocytosis (CME) and its core endocytic machinery are evolutionarily conserved... more Clathrin-mediated endocytosis (CME) and its core endocytic machinery are evolutionarily conserved across all eukaryotes. In mammals, the heterotetrameric adaptor protein complex-2 (AP-2) sorts plasma membrane (PM) cargoes into vesicles via the recognition of motifs based on Tyr or di-Leu in their cytoplasmic tails. However, in plants, very little is known about how PM proteins are sorted for CME and whether similar motifs are required. In Arabidopsis (Arabidopsis thaliana), the brassinosteroid (BR) receptor BR INSENSITIVE1 (BRI1) undergoes endocytosis, which depends on clathrin and AP-2. Here, we demonstrate that BRI1 binds directly to the medium AP-2 subunit (AP2M). The cytoplasmic domain of BRI1 contains five putative canonical surface-exposed Tyr-based endocytic motifs. The Tyr-to-Phe substitution in Y898KAI reduced BRI1 internalization without affecting its kinase activity. Consistently, plants carrying the BRI1Y898F mutation were hypersensitive to BRs. Our study demonstrates th...
Brassinosteroids (BRs) are a group of polyhydroxylated plant steroid hormones that are crucial fo... more Brassinosteroids (BRs) are a group of polyhydroxylated plant steroid hormones that are crucial for many aspects of a plant's life. BRs were originally characterized for their function in cell elongation, but it is becoming clear that they play major roles in plant growth, development, and responses to several stresses such as extreme temperatures and drought. A BR signaling pathway from cell surface receptors to central transcription factors has been well characterized. Here, we summarize recent progress toward understanding the BR pathway, including BR perception and the molecular mechanisms of BR signaling. Next, we discuss the roles of BRs in development and stress responses. Finally, we show how knowledge of the BR pathway is being applied to manipulate the growth and stress responses of crops. These studies highlight the complex regulation of BR signaling, multiple points of crosstalk between BRs and other hormones or stress responses, and the finely tuned spatiotemporal regulation of BR signaling.
Soil microbial communities hold great potential for sustainable and ecologically compatible agric... more Soil microbial communities hold great potential for sustainable and ecologically compatible agriculture. Although numerous plant-beneficial bacterial strains from a wide range of taxonomic groups have been reported, very little evidence is available on the plant-beneficial role of bacteria from the genus Caulobacter. Here, the mode of action of a Caulobacter strain, designated RHG1, which had originally been identified through a microbial screen for plant growth-promoting (PGP) bacteria in maize (Zea mays), is investigated in Arabidopsis thaliana. RHG1 colonized both roots and shoots of Arabidopsis, promoted lateral root formation in the root, and increased leaf number and leaf size in the shoot. The genome of RHG1 was sequenced and was utilized to look for PGP factors. Our data revealed that the bacterial production of nitric oxide, auxins, cytokinins, or 1-aminocyclopropane-1-carboxylate deaminase as PGP factors could be excluded. However, the analysis of brassinosteroid mutants s...
Proceedings of the National Academy of Sciences of the United States of America, Feb 5, 2018
Plants largely rely on plasma membrane (PM)-resident receptor-like kinases (RLKs) to sense extrac... more Plants largely rely on plasma membrane (PM)-resident receptor-like kinases (RLKs) to sense extracellular and intracellular stimuli and coordinate cell differentiation, growth, and immunity. Several RLKs have been shown to undergo internalization through the endocytic pathway with a poorly understood mechanism. Here, we show that endocytosis and protein abundance of thebrassinosteroid (BR) receptor, BR INSENSITIVE1 (BRI1), are regulated by plant U-box (PUB) E3 ubiquitin ligase PUB12- and PUB13-mediated ubiquitination. BR perception promotes BRI1 ubiquitination and association with PUB12 and PUB13 through phosphorylation at serine 344 residue. Loss of PUB12 and PUB13 results in reduced BRI1 ubiquitination and internalization accompanied with a prolonged BRI1 PM-residence time, indicating that ubiquitination of BRI1 by PUB12 and PUB13 is a key step in BRI1 endocytosis. Our studies provide a molecular link between BRI1 ubiquitination and internalization and reveal a unique mechanism of ...
The mechanism of cellulose synthesis has been studied by characterizing the motility of cellulose... more The mechanism of cellulose synthesis has been studied by characterizing the motility of cellulose synthase complexes tagged with a fluorescent protein; however, this approach has been used exclusively on the hypocotyl of Arabidopsis thaliana. Here we characterize cellulose synthase motility in the model grass, Brachypodium distachyon. We generated lines in which mEGFP is fused N-terminal to BdCESA3 or BdCESA6 and which grew indistinguishably from the wild type (Bd21-3) and had dense fluorescent puncta at or near the plasma membrane. Measured with a particle tracking algorithm, the average speed of GFP-BdCESA3 particles in the mesocotyl was 164 ± 78 nm min(-1) (error gives standard deviation [SD], n = 1451 particles). Mean speed in the root appeared similar. For comparison, average speed in the A. thaliana hypocotyl expressing GFP-AtCESA6 was 184 ± 86 nm min(-1) (n = 2755). For B. distachyon, we quantified root diameter and elongation rate in response to inhibitors of cellulose (dich...
The polysaccharide cellulose is the main component of plant cell walls, so it is the most abundan... more The polysaccharide cellulose is the main component of plant cell walls, so it is the most abundant polymer on the earth. While it is widely used in industry due to its remarkable properties, such as renewability and biodegradability, its biosynthesis is still not well understood. The large transmembrane protein complex responsible for synthesizing cellulose contains several cellulose synthase A (CESA) subunits that polymerize UDP glucose into the constituent glucan chains of cellulose. Here, we used variable angle epi-fluorescence microscopy in combination with single-particle tracking to characterize the motion of GFP labeled CESA complexes in the root and mesocotyl of Brachypodium distachyon seedlings that are a 3 to 4 days old. We show that CESA complexes move through the plasma membrane at approximately 165 nm/minute. Their motion is known to be guided by cortical microtubules, but no molecular motors are involved. Rather, the motion is thought to be driven by the polymerization and crystallization of the cellulose. A mean-squared displacement analysis shows that CESA complexes move diffusively on short time scales and undergo a transition to super-diffusive motion on a time scale of about 10 s. We also report on the effect of actin and microtubule inhibitors on CESA motion.
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Papers by Derui Liu