Structural and mechanochemical microtubule-associated proteins in plant cell function.

摘要

Plant cells use the microtubule cytoskeleton to create axes of cellular expansion and division via the formation of a variety of microtubule arrays, including the interphase cortical array, pre-prophase band, phragmoplast, and spindle apparatus. The formation of these arrays is influenced by the biochemical and structural properties of microtubules; comprised mainly of α- and β-tubulin heterodimers, microtubules undergo stages of rapid shortening and slow elongation. This innate dynamic character, termed dynamic instability, allows microtubules to rapidly appear, disappear, and linger for various periods of time.; A group of auxiliary proteins, termed microtubule-associated proteins (MAPS), regulate microtubule dynamicity and organization. MAN can be divided into two classes—structural MAPs and mechanochemical MAPs. Structural MAPs play a role in microtubule morphology and assembly by affecting dynamic instability, while mechanochemical MAPs move along the microtubule and are required for intracellular transport and microtubule organization.; The work presented here has provided evidence that a MAP/microtubule interaction is necessary for stomatal opening. Stomata are found mainly on leaves and consist of a pair of guard cells that regulate gas exchange by opening and closing. Using different classes of microtubule inhibitors, we present data that is consistent with a model, whereby a MAP/microtubule interaction occurs in the early signaling events of stomatal opening.; I have also investigated the function of a putative mechanochemical MAP, ATK1, in mitosis and meiosis. This protein is predicted to be a kinesin based upon homology to known kinesins, and previous studies suggest that it functions in cell division. Here, I have confirmed this hypothesis by showing that ATK1 functions in spindle assembly during meiosis and mitosis. Furthermore, I have expressed the ATK1 protein and used it for in vitro assays. This biochemical data shows that ATK1 is a minus-end directed kinesin that moves non-processively along the microtubule. Overall, the experiments with ATK1 have provided insight into the mechanisms that plant cells use to assemble and maintain meiotic and mitotic spindles.