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End date: 2019Subject: search.filters.subject.Arabidopsis

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    OsWAKL21, a putative receptor of rice cell wall damage activates alternate signaling in rice and Arabidopsis to induce immunity
    (American Phytopathological Society, 2019) Malukani, K. K.; Ranjan, A.; Hota, S. J.; Patel, H. K.; Sonti, Ramesh V.
    Xanthomonas oryzae pv. oryzae (Xoo) causes the serious bacterial blight disease of rice. As part of its virulence repertoire, Xoo secretes various cell wall degrading enzymes (CWDEs) such as cellulases, xylanases and a Lipase/esterase (LipA). Conversely, treatment of rice tissues with any of these purified enzymes activates immune responses. Plants sense this cell wall damage as a mark of infection and induce immune responses. Very little information is available about the plant functions that are involved in the elaboration of cell wall damage induced immune responses. Transcriptome analyses revealed a rice cell wall-associated receptor kinase, OsWAKL21 that is upregulated following treatment with either LipA or Xoo. VIGS mediated downregulation of OsWAKL21 attenuates LipA induced immune responses. Overexpression of OsWAKL21 in rice mimics LipA treatment in induction of immune responses, activation of JA pathway and enhanced expression of defence related genes, indicating that it plays an important role in elaboration of LipA induced immune responses. Ectopic expression of OsWAKL21 in Arabidopsis also activates plant immune responses. OsWAKL21 is a moonlighting kinase having in vitro kinase and guanylate cyclase activities. Interestingly, OsWAKL21 needs kinase activity to activate immune responses in rice while in Arabidopsis it needs the guanylate cyclase activity. Thus OsWAKL21 is activating similar immune responses in two different species but via different mechanisms.
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    IBR5 regulates leaf serrations development via modulation of the expression of PIN1
    (MDPI AG, 2019) Kong, Xiuzhen; Huang, Guoqiang; Xiong, Yali; Zhao, Chunyan; Wang, Jun; Song, Xiaoyun; Giri, Jitender; Zuo, Kaijing
    Biodiversity in plant shape is mainly attributable to the diversity of leaf shape, which is largely determined by the transient morphogenetic activity of the leaf margin that creates leaf serrations. However, the precise mechanism underlying the establishment of this morphogenetic capacity remains poorly understood. We report here that INDOLE-3-BUTYRIC ACID RESPONSE 5 (IBR5), a dual-specificity phosphatase, is a key component of leaf-serration regulatory machinery. Loss-of-function mutants of IBR5 exhibited pronounced serrations due to increased cell area. IBR5 was localized in the nucleus of leaf epidermis and petiole cells. Introducing a C129S mutation within the highly conserved VxVHCx2GxSRSx5AYLM motif of IBR5 rendered it unable to rescue the leaf-serration defects of the ibr5-3 mutant. In addition, auxin reporters revealed that the distribution of auxin maxima was expanded ectopically in ibr5-3. Furthermore, we found that the distribution of PIN1 on the plasma membrane of the epidermal and cells around the leaf vein was compromised in ibr5-3. We concluded that IBR5 is essential for the establishment of PIN-FORMED 1 (PIN1)-directed auxin maxima at the tips of leaf serration, which is vital for the elaborated regulation during its formation.
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    Whole mount in situ localization of miRNAs and target mRNA transcripts in plants
    (Springer Nature Publishing AG, 2019) Gautam, Vibhav; Singh, Archita; Verma, Swati; Singh, Sharmila; Chatterjee, Sourav; Sarkar, Ananda K.
    The functional characterization of miRNAs often involves understanding of their spatiotemporal expression, which mostly relies on reporter-based or in situ hybridization studies. The available in situ localization methods follow separate protocols for pre-hybridization, hybridization, post-hybridization, and detection steps for both miRNA and mRNA transcripts in plants. In this study, we present a single method which can be used for whole mount in situ localization of both miRNAs and mRNAs in different plant tissues. Our modified method provides enhanced sensitivity for the localization of miRNA and their target transcripts. Consequently, a less laborious, time-saving, economic and efficient method has been proposed by the modification of pre-hybridization, hybridization, post-hybridization and detection steps.
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    The Ca2+ channel CNGC19 regulates Arabidopsis defense against spodoptera herbivory
    (American Society of Plant Biologists, 2019) Meena, Mukesh Kumar; Prajapati, Ramgopal; Krishna, Deepthi; Divakaran, Keerthi; Pandey, Yogesh; Reichelt, Michael; Mathew, M.K.; Boland, Wilhelm; Mithöfer, Axel; Vadassery, Jyothilakshmi
    Cellular calcium elevation is an important signal used by plants for recognition and signaling of environmental stress. Perception of the generalist insect, Spodoptera litura, by Arabidopsis thaliana activates cytosolic Ca2+ elevation, which triggers downstream defense. However, not all the Ca2+ channels generating the signal have been identified, nor are their modes of action known. We report on a rapidly activated, leaf vasculature- and plasma membrane-localized, CYCLIC NUCLEOTIDE GATED CHANNEL19 (CNGC19), which activates herbivory-induced Ca2+ flux and plant defense. Loss of CNGC19 function results in decreased herbivory defense. The cngc19 mutant shows aberrant and attenuated intra-vascular Ca2+ fluxes. CNGC19 is a Ca2+ permeable channel, as hyperpolarization of CNGC19-expressing Xenopus oocytes in the presence of both cAMP and Ca2+ results in Ca2+ influx. Breakdown of Ca2+-based defence in cngc19 mutants leads to a decrease in herbivory-induced JA-Ile biosynthesis and expression of JA responsive genes. cngc19 mutants are deficient in aliphatic glucosinolate accumulation and hyperaccumulate its precursor, methionine. CNGC19 modulates aliphatic glucosinolate biosynthesis in tandem with BRANCHED-CHAIN AMINO ACID TRANSAMINASE4 (BCAT4), which is involved in the chain elongation pathway of Met-derived glucosinolates. Furthermore, CNGC19 interacts with herbivory-induced CALMODULIN2 (CaM2) in planta. Together, our work reveals a key mechanistic role for the Ca2+ channel CNGC19 in the recognition of herbivory and the activation of defense signaling.
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    Interaction map of Arabidopsis mediator complex expounding its topology
    (Oxford University Press, 2019) Maji, Sourobh; Dahiya, Pradeep; Waseem, Mohd; Dwivedi, Nidhi; Bhat, Divya S.; Dar, Tanvir H.; Thakur, Jitendra K.
    Understanding of mechanistic details of Mediator functioning in plants is impeded as the knowledge of subunit organization and structure is lacking. In this study, an interaction map of Arabidopsis Mediator complex was analyzed to understand the arrangement of the subunits in the core part of the complex. Combining this interaction map with homologybased modeling, probable structural topology of core part of the Arabidopsis Mediator complex was deduced. Though the overall topology of the complex was similar to that of yeast, several differences were observed. Many interactions discovered in this study are not yet reported in other systems. AtMed14 and AtMed17 emerged as the key component providing important scaffold for the whole complex. AtMed6 and AtMed10 were found to be important for linking head with middle and middle with tail, respectively. Some Mediator subunits were found to form homodimers and some were found to possess transactivation property. Subcellular localization suggested that many of the Mediator subunits might have functions beyond the process of transcription. Overall, this study reveals role of individual subunits in the organization of the core complex, which can be an important resource for understanding the molecular mechanism of functioning of Mediator complex and its subunits in plants.
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    Two chloroplast-localized proteins: AtNHR2A and AtNHR2B, contribute to callose deposition during nonhost disease resistance in Arabidopsis
    (American Phytopathological Society, 2018) Singh, Raksha; Lee, Seonghee; Ortega, Laura; Ramu, Vemanna S.; Senthil-Kumar, Muthappa; Blancaflor, Elison B.; Rojas, Clemencia M.; Mysore, Kirankumar S.
    Plants are naturally resistant to most pathogens through a broad and durable defense response called nonhost disease resistance. Nonhost disease resistance is a complex process that includes preformed physical and chemical barriers and induced responses. In spite of its importance, many components of nonhost disease resistance remain to be identified and characterized. Using virus-induced gene silencing in Nicotiana benthamiana, we discovered a novel gene that we named NbNHR2 (N. benthamiana nonhost resistance 2). NbNHR2-silenced plants were susceptible to the non-adapted pathogen Pseudomonas syringae pv. tomato T1 that does not cause disease in wild-type or non-silenced N. benthamiana plants. We found two orthologous genes in Arabidopsis thaliana: AtNHR2A and AtNHR2B. Similar to the results obtained in N. benthamiana, Atnhr2a and Atnhr2b mutants were susceptible to the non-adapted bacterial pathogen of A. thaliana, P. syringae pv. tabaci. We further found that these mutants were also defective in callose deposition. AtNHR2A and AtNHR2B fluorescent protein fusions transiently expressed in N. benthamiana localized predominantly to chloroplasts and a few unidentified dynamic puncta. RFP-AtNHR2A and AtNHR2B-GFP displayed overlapping signals in chloroplasts indicating that the two proteins could interact; a notion supported by co-immunoprecipitation studies. We propose that AtNHR2A and AtNHR2B are new components of a chloroplast-signaling pathway that activates callose deposition to the cell wall in response to bacterial pathogens.
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    A protein phosphatase 2C, AP2C1 interacts with and negatively regulates the function of CIPK9 under potassium deficient conditions in Arabidopsis
    (Oxford University Press, 2018) Singh, Amarjeet; Yadav, Akhilesh K.; Kaur, Kanwaljeet; Sanyal, Sibaji K.; Jha, Saroj K.; Fernandes, Joel L.; Sharma, Pankhuri; Tokas, Indu; Pandey, Amita; Luan, Sheng; Pandey, Girdhar K.
    Potassium (K+) is a major macronutrient required for plant growth. In response to low- K+ condition, an adaptive mechanism entails activation of the Ca2+ signaling network consisting of calcineurin B-like proteins (CBLs) and their interacting kinases (CIPKs) in plants. The CBL-interacting protein kinase 9 (CIPK9) is previously implicated in low-K+ responses in Arabidopsis thaliana. Here, we report a protein phosphatase 2C (PP2C), AP2C1, as an interactor of CIPK9. Fluorescence resonance energy transfer (FRET), bimolecular fluorescence complementation (BiFC) and co-localization analyses revealed that CIPK9 and AP2C1 interact in the cytoplasm. AP2C1 dephosphorylates the auto-phosphorylated form of CIPK9 in vitro, presenting a regulatory mechanism for CIPK9 function. Furthermore, genetic and molecular analysis revealed that ap2c1 null mutants (ap2c1-1 and ap2c1-2) are tolerant to low-K+ conditions, retained higher K+ content and showed higher expression of K+ deficiency related genes contrary to cipk9 mutants (cipk9-1 and cipk9-2). In contrast, transgenic plants overexpressing AP2C1 were sensitive to low-K+ conditions. Thus, this study shows that AP2C1 and CIPK9 interact to regulate K+-deficiency responses in Arabidopsis. CIPK9 functions as positive regulator whereas, AP2C1 acts as a negative regulator of Arabidopsis root growth and seedling development under low-K+ conditions.
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    A mechanistic framework for auxin dependent Arabidopsis root hair elongation to low external phosphate
    (Nature Publishing Group, 2018) Bhosale, Rahul; Giri, Jitender; Pandey, Bipin K.; Giehl, Ricardo F.H.; Hartmann, Anja; Traini, Richard; Truskina, Jekaterina; Leftley, Nicola; Hanlon, Meredith; Swarup, Kamal; Rashed, Afaf; Voß, Ute; Alonso, Jose; Stepanova, Anna; Yun, Jeonga; Ljung, Karin; Brown, Kathleen M.; Lynch, Jonathan P.; Dolan, Liam; Vernoux, Teva; Bishopp, Anthony; Wells, Darren; Wirén, Nicolaus von; Bennett, Malcolm J.; Swarup, Ranjan
    Phosphate (P) is an essential macronutrient for plant growth. Roots employ adaptive mechanisms to forage for P in soil. Root hair elongation is particularly important since P is immobile. Here we report that auxin plays a critical role promoting root hair growth in Arabidopsis in response to low external P. Mutants disrupting auxin synthesis (taa1) and transport (aux1) attenuate the low P root hair response. Conversely, targeting AUX1 expression in lateral root cap and epidermal cells rescues this low P response in aux1. Hence auxin transport from the root apex to differentiation zone promotes auxin-dependent hair response to low P. Low external P results in induction of root hair expressed auxin-inducible transcription factors ARF19, RSL2, and RSL4. Mutants lacking these genes disrupt the low P root hair response. We conclude auxin synthesis, transport and response pathway components play critical roles regulating this low P root adaptive response.
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    FCS-like zinc finger 6 and 10 repress SnRK1 signalling in Arabidopsis
    (John Wiley & Sons, 2018) Jamsheer, Muhammed K.; Sharma, Manvi; Singh, Dhriti; Mannully, Chanchal Thomas; Jindal, Sunita; Shukla, Brihaspati Narayan; Laxmi, Ashverya
    SNF1-Related Protein Kinase 1 (SnRK1) is a central regulator of plant growth during energy starvation. The FCS-Like Zinc finger (FLZ) proteins are recently identified adaptor proteins which facilitate the interaction of SnRK1 with other proteins. In this study, we identified that two starvation-induced FLZ genes, FLZ6 and FLZ10, work as repressors of SnRK1 signalling. The reduced expression of these genes resulted in an increase in the level of SnRK1α1, which is the major catalytic subunit of SnRK1. This resulted in a concomitant increase in the phosphorylated protein and SnRK1 activity in the flz6 and flz10 mutants. FLZ6 and FLZ10 specifically interact with SnRK1α subunits in the cytoplasmic foci which colocalized with the endoplasmic reticulum. In physiological assays, similar to SnRK1α1 overexpression line, flz mutants showed compromised growth. Further, the growth promotion in response to favourable growth conditions was found to be attenuated in the mutants. The enhanced SnRK1 activity in the mutants resulted in a reduction in the level of phosphorylated RIBOSOMAL S6 KINASE and the expression of E2Fa and its targets indicating that TARGET OF RAPAMYCIN-dependent promotion of protein synthesis and cell cycle progression is impaired. Taken together, this study uncovers a plant-specific modulation of SnRK1 signalling.
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    Arabidopsis RSS1 mediates cross-talk between glucose and light signaling during hypocotyl elongation growth
    (Nature Publishing Group, 2017) Singh, Manjul; Gupta, Aditi; Singh, Dhriti; Khurana, Jitendra P.; Laxmi, Ashverya
    Plants possess exuberant plasticity that facilitates its ability to adapt and survive under challenging environmental conditions. The developmental plasticity largely depends upon cellular elongation which is governed by a complex network of environmental and phytohormonal signals. Here, we report role of glucose (Glc) and Glc-regulated factors in controlling elongation growth and shade response in Arabidopsis. Glc controls shade induced hypocotyl elongation in a dose dependent manner. We have identified a Glc repressed factor REGULATED BY SUGAR AND SHADE1 (RSS1) encoding for an atypical basic helix-loop-helix (bHLH) protein of unknown biological function that is required for normal Glc actions. Phenotype analysis of mutant and overexpression lines suggested RSS1 to be a negative regulator of elongation growth. RSS1 affects overall auxin homeostasis. RSS1 interacts with the elongation growth-promoting proteins HOMOLOG OF BEE2 INTERACTING WITH IBH 1 (HBI1) and BR ENHANCED EXPRESSION2 (BEE2) and negatively affects the transcription of their downstream targets such as YUCs, INDOLE-3-ACETIC ACID INDUCIBLE (IAAs), LONG HYPOCOTYL IN FAR-RED1 (HFR1), HOMEOBOX PROTEIN 2 (ATHB2), XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASES (XTHs) and EXPANSINS. We propose, Glc signals might maintain optimal hypocotyl elongation under multiple signals such as light, shade and phytohormones through the central growth regulatory bHLH/HLH module.