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As plant cells are glued to one another, the control of the direction of cell elongation and division is important for plant morphogenesis. During directional cell growth, microtubules align into parallel arrays that promote cell elongation in a direction perpendicular to the microtubule arrays. In my past research, I analyzed the contribution of Arabidopsis NIMA-related kinase 6 (NEK6) in microtubule organization. In the nek6 mutant, the cortical microtubules were stabilized, whereas they were destabilized by NEK6 overexpression. Interestingly, the NEK6 protein localized to shrinking microtubules. I identified the β-tubulin phosphorylation sites of NEK6, and found that a nonphosphorylatable mutation of the phosphorylation site remarkably promoted polymerization of β-tubulins. Thus, NEK6 induces microtubule depolymerization through the phosphorylation of β-tubulin. Phenotypically, I observed ectopic outgrowth in epidermal cells and wavy hypocotyls in the nek6 mutants and found that those phenotypes are due to hyper-sensitivity to cell shape or hypocotyl bending. Consistently, microtubules in nek6 mutants were hypersensitive to mechanical perturbations. Taken together, these results indicate that NEK6 reduces the microtubule response to mechanical stress in the wild type, arguably via its function on microtubule depolymerization. In my current AgSk project, I investigate how plants determine cell division plane orientation (CDPO). Previously, it was revealed that the pattern of mechanical stress, which depends on tissue growth and shape, channels CDPO and that preprophase band is required for CDPO robustness; yet the link between mechanical stress and preprophase band dynamics and function remains unknown. Using the Arabidopsis shoot apical meristem as an experimental system, I will first draw a correlation map between microtubule dynamics, cell shape and growth, and CDPO and identify the spatio-temporal scales at which these correlations exist. Next, I will test the corresponding causalities using the trm678 mutant which does not form a preprophase band and is affected in CDPO robustness. Thus, I will challenge the robustness of cell divisions and set the stage to characterize the mechanotransduction pathways controlling CDPO.
I got a Master in Science, Division of Biological Science at Okayama University. Afterward I received my PhD in March 2018 in the same University (Division of Earth, Life, and Molecular Sciences, Graduate School of Natural Science and Technology). This PhD project was focused on the molecular mechanism of plant cell elongation by analyzing Arabidopsis NIMA related kinase 6. The mechanism of cell division plane orientation is hot topic in plant biology and the laboratory in ENS LYON developed unique methods involving biomechanics of division tissue. Thanks to the AgreenSkills+ fellowship, I recently join this institution to tackle this issue.
Otani K, Ishizaki K, Nishihama R, Takatani S, Kohchi T, Takahashi T, Motose H, 2018. An evolutionarily conserved NIMA-related kinase directs rhizoid tip growth in the basal land plant Marchantia polymorpha. Development, 145 (5), dev154617. Doi: 10.1242/dev.154617.
Takatani S, Ozawa S, Yagi N, Hotta T, Hashimoto T, Takahashi Y, Takahashi T, Motose H, 2017. Directional cell expansion requires NIMA-related kinase 6 (NEK6)-mediated cortical microtubule destabilization. Scientific Reports. 7(1):7826. Doi: 10.1038/s41598-017-08453-5.
Takatani S, Hirayama T, Hashimoto T, Takahashi T, Motose H, 2015. Abscisic acid induces ectopic outgrowth in epidermal cells through cortical microtubule reorganization in Arabidopsis thaliana. Scientific Reports, 5, 11364. Doi: 10.1038/srep11364.
Takatani S, Otani K, Kanazawa M, Takahashi T Motose H, 2015. Structure, function and evolution of plant NIMArelated kinases: Implication for the phosphorylationdependent microtubule regulation. Journal of Plant Research 128(6), 875-891.
Motose H, Takatani S, Ikeda T, Takahashi T, 2012. NIMArelated kinases regulate directional cell growth and organ development through microtubule function in Arabidopsis thaliana. Plant Signaling & Behavior, 7, 1552-1555.