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Involvement of mitogen-activated protein kinase signalling in plant microtubule function Walia, Ankit


Plants have developed sophisticated signalling networks that are involved in mediating developmental transitions and environmental signals. Mitogen-activated protein kinases (MPKs) are a class of signalling proteins that are involved in cellular processes that help plants to detect and initiate appropriate responses to numerous development and environmental inputs. The microtubule cytoskeleton plays a pivotal role in plant development and morphogenesis, although the mechanisms that regulate the microtubule-associated proteins and microtubule functions in plant cells are not well understood. I investigated whether perturbations in the microtubule organization triggered by the MICROTUBULE ORGANIZATION] temperature-sensitive mutant(morl-l) could lead to altered transcriptional activity, with a particular interest in the genes encoding signal transduction components. I showed that perturbations in the microtubule cytoskeleton, achieved through the microtubule disruption phenotype of mor1-1, led to changes in the expression of gene transcripts associated with diverse cellular processes, including changes in the expression of the PROPYZAMIDE HYPERSENSITIVE 1(PHS1) gene, a member of MPK-specific signal transduction pathway, which has been previously implicated in mediating cortical microtubule functions in plant cells. Through biochemical, cell biological and genetic tools, I identified MPK18 as one of the MPKs that interacts with the PHS1 phosphatase and demonstrated through reverse genetics analysis that manipulation of MPK18 results in conditional and subtle defects in the microtubule functionality. In contrast, analysis of MPK12, which was shown to also interact with PHS1, identified no microtubule-specific function. My live cell imaging studies revealed that the absence of MPK18 protein appears to have no effect on microtubule plus end growth and shrinkage rates, indicating that MPK18 indirectly influences microtubule functions. Based on the genetic analysis, MOR1 itself does not appear to be a target of the putative MPK18 signalling module. Preliminary attempts to obtain evidence for direct impacts of PHS activity on MOR1 failed to demonstrate that manipulation of PHS1 altered either subcellular localization or phosphorylation status of the MOR1 protein. These results provide a platform that should facilitate future investigations aimed at understanding the role of MPK signalling in the regulation of plant microtubule functions.

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