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    The small RNA biogenesis in rice is regulated by MAP kinase-mediated OsCDKD phosphorylation
    (John Wiley & Sons, 2024) Singh, Dhanraj; Verma, Neetu; Rengasamy, Balakrishnan; Banerjee, Gopal; Sinha, Alok Krishna
    CDKs are the master regulator of cell division and their activity is controlled by the regulatory subunit cyclins and phosphorylation by the CAKs. However, the role of MAP kinases in regulating plant cell cycle or CDKs have not been explored. Here, we report that the MAP kinases OsMPK3, OsMPK4, and OsMPK6 physically interact and phosphorylate OsCDKD and its regulatory subunit OsCYCH in rice. MAP kinases phosphorylate CDKD at Ser-168 and Thr-235 residues in OsCDKD. The MAP kinase-mediated phosphorylation of OsCDKD is required for its activation to control the small RNA biogenesis. The phosphodead version of OsCDKD fails to activate the C-terminal domain of RNA Polymerase II, thereby negatively impacting small RNA transcription. Further, the overexpression lines of wild-type (WT) OsCDKD and phosphomimic OsCDKD show increased root growth, plant height, tiller number, panicle number, and seed number in comparison to WT, phosphodead OsCDKD-OE, and kinase-dead OsCDKD-OE plants. In a nutshell, our study establishes a novel regulation of OsCDKD by MAPK-mediated phosphorylation in rice. The phosphorylation of OsCDKD by MAPKs imparts a positive effect on rice growth and development by regulating miRNAs transcription.
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    Phosphorylation of AGO1a by MAP kinases is required for miRNA mediated resistance against Xanthomonas oryzae pv. oryzae infection in rice
    (Elsevier B.V., 2024) Singh, Kirti; Sharma, Deepika; Bhagat, Prakash Kumar; Tayyeba, Sumaira; Noryang, Stanzin; Sinha, Alok Krishna
    Bacterial leaf blight is a devastating disease caused by Xanthomonas oryzae pv. oryzae (Xoo) which causes severe crop loss in rice. The molecular mechanism that initiates defense against such pathogens remains unexplored. Reports have suggested crucial role of several miRNAs in regulating immune responses in plants. Argonaute (AGO) proteins have been implicated in imparting immunity against pathogens by using small RNAs as guide molecules. Here, we show that phosphorylation of rice AGO1a by MAP kinases is required for miRNA expression regulation during Xoo infection. AGO1a is induced in response to pathogen infection and is under the control of SA signaling pathway. The pathogen responsive MAP kinases MPK3, MPK4 and MPK6, interact with AGO1a in planta and can phosphorylate the protein in vitro. Overexpression of AGO1a extends disease resistance against Xoo in rice and leads to a higher accumulation of miRNAs. Conversely, overexpression of a non phosphorylatable mutant protein aggravates disease susceptibility and remarkably suppresses the miRNA expression levels. At a molecular level, phosphorylation of AGO1a by MAP kinase is required for increased accumulation of miRNAs during pathogen challenge. Taken together, the data suggests that OsAGO1a is a direct phosphorylation target of MAP kinases and this phosphorylation is crucial for its role in imparting disease resistance.
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    MAP kinases may mediate regulation of the cell cycle in rice by E2F2 phosphorylation
    (John Wiley & Sons, 2023) Singh, Dhanraj; Banerjee, Gopal; Verma, Neetu; Sinha, Alok Krishna
    E2F is the key transcription factor that determines the proliferative status of cells by regulating the G1/S phase of the cell cycle. In this study, we show that in rice (Oryza sativa), OsE2F2 is a phosphorylation target of MAP kinases. The MAP kinases OsMPK3, OsMPK4, and OsMPK6 interact with and phosphorylate OsE2F2. Next, we determined the serine and threonine residues that could play a role in the phosphorylation of OsE2F2. Subsequently, our study suggests a possible link between MAP kinase-mediated OsE2F2 phosphorylation and its impact on DNA proliferation in the roots of rice seedlings. Finally, we found positive feedback regulation of OsMPK4 by OsE2F2. Therefore, our study hints at the potential impact of MAP kinase signaling on the cell cycle of rice plants.
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    FERONIA, the kinase that phosphorylates PhyB
    (Elsevier B.V., 2023) Sharma, Shambhavi; Prasad, Manoj
    The phosphorylation status of phyB changes dynamically in response to environmental conditions and critically governs the corresponding plant’s responses. However, the kinase(s) that phosphorylates phyB is/are still unknown. Liu et al. have not only identified the kinase that phosphorylates phyB but also revealed its biological implications during salt stress.
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    AtSWEET11 and AtSWEET12: the twin traders of sucrose
    (Elsevier B.V., 2022) Fatima, Urooj; Anjali, Anjali; Senthil-Kumar, Muthappa
    AtSWEET11 and AtSWEET12 are central players in phloem loading and long-distance sucrose translocation. During drought stress, these transporters enhance sucrose transport from shoot to root, increasing root proliferation. Chen et al. have now unravelled novel aspects of sucrose transport regulation, occurring via AtSWEET11 and AtSWEET12 phosphorylation and oligomerisation.
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    Regulating the regulator: nitric oxide control of post-translational modifications
    (John Wiley & Sons, Inc., 2020) Gupta, Kapuganti Jagadis; Kolbert, Zsuzsanna; Durner, Jorg; Lindermayr, Christian; Corpas, Francisco J.; Brouquisse, Renaud; Barroso, Juan B.; Saima, Umbreen; Palma, José M; Hancock, John T.; Petrivalsky, Marek; Wendehenne, David; Loake, Gary J.
    Nitric oxide (NO) is perfectly suited for duties as a redox signalling molecule. A key route for NO bioactivity occurs via protein S‐nitrosation, the addition of a NO moiety to a protein cysteine (Cys) thiol (‐SH) to form a S‐nitrosothiol (SNO). This process is thought to underpin a myriad of cellular processes in plants linked to development, environmental responses and immune function. Here we collate emerging evidence showing that NO bioactivity regulates a growing number of diverse post‐translational modifications (PTMs) including SUMOylation, phosphorylation, persulfidation and acetylation. We provide examples of how NO orchestrates these processes to mediate plant adaptation to a variety of cellular cues.
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    Regulation of WRKY46 transcription factor function by mitogen-activated protein kinases in Arabidopsis thaliana
    (Frontiers Media S.A., 2016) Sheikh, Arsheed H.; Eschen-Lippold, Lennart; Pecher, Pascal; Hoehenwarter, Wolfgang; Sinha, Alok Krishna; Scheel, Dierk; Lee, Justin
    Mitogen-activated protein kinase (MAPK) cascades are central signaling pathways activated in plants after sensing internal developmental and external stress cues. Knowledge about the downstream substrate proteins of MAPKs is still limited in plants. We screened Arabidopsis WRKY transcription factors as potential targets downstream of MAPKs, and concentrated on characterizing WRKY46 as a substrate of the MAPK, MPK3. Mass spectrometry revealed in vitro phosphorylation of WRKY46 at amino acid position S168 by MPK3. However, mutagenesis studies showed that a second phosphosite, S250, can also be phosphorylated. Elicitation with pathogen-associated molecular patterns (PAMPs), such as the bacterial flagellin-derived flg22 peptide led to in vivo destabilization of WRKY46 in Arabidopsis protoplasts. Mutation of either phosphorylation site reduced the PAMP-induced degradation of WRKY46. Furthermore, the protein for the double phosphosite mutant is expressed at higher levels compared to wild-type proteins or single phosphosite mutants. In line with its nuclear localization and predicted function as a transcriptional activator, overexpression of WRKY46 in protoplasts raised basal plant defense as reflected by the increase in promoter activity of the PAMP-responsive gene, NHL10, in a MAPK-dependent manner. Thus, MAPK-mediated regulation of WRKY46 is a mechanism to control plant defense.