Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Center for Frontier Research, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan.
Mass Spectrometry and Microscopy Unit, Center for Sustainable Resource Science, RIKEN, 1-7-22 Suehiro, Tsurumi, Yokohama, Kanagawa 230-0045, Japan.
Curr Biol. 2017 Aug 21;27(16):2522-2528.e4. doi: 10.1016/j.cub.2017.06.059. Epub 2017 Aug 10.
Spatial control of cell-wall deposition is essential for determining plant cell shape [1]. Rho-type GTPases, together with the cortical cytoskeleton, play central roles in regulating cell-wall patterning [2]. In metaxylem vessel cells, which are the major components of xylem tissues, active ROP11 Rho GTPases form oval plasma membrane domains that locally disrupt cortical microtubules, thereby directing the formation of oval pits in secondary cell walls [3-5]. However, the regulatory mechanism that determines the planar shape of active Rho of Plants (ROP) domains is still unknown. Here we show that IQD13 associates with cortical microtubules and the plasma membrane to laterally restrict the localization of ROP GTPase domains, thereby directing the formation of oval secondary cell-wall pits. Loss and overexpression of IQD13 led to the formation of abnormally round and narrow secondary cell-wall pits, respectively. Ectopically expressed IQD13 increased the presence of parallel cortical microtubules by promoting microtubule rescue. A reconstructive approach revealed that IQD13 confines the area of active ROP domains within the lattice of the cortical microtubules, causing narrow ROP domains to form. This activity required the interaction of IQD13 with the plasma membrane. These findings suggest that IQD13 positively regulates microtubule dynamics as well as their linkage to the plasma membrane, which synergistically confines the area of active ROP domains, leading to the formation of oval secondary cell-wall pits. This finding sheds light on the role of microtubule-plasma membrane linkage as a lateral fence that determines the planar shape of Rho GTPase domains.
细胞壁沉积的空间控制对于确定植物细胞形状至关重要[1]。Rho 型 GTPase 与皮质细胞骨架一起，在调节细胞壁模式形成中起着核心作用[2]。在木质部组织的主要成分——次生木质部导管细胞中，活性 ROP11 Rho GTPase 形成椭圆形的质膜域，局部破坏皮质微管，从而指导次生细胞壁中椭圆形凹陷的形成[3-5]。然而，决定活性植物 Rho（ROP）域平面形状的调节机制仍不清楚。在这里，我们表明 IQD13 与皮质微管和质膜结合，从而限制 ROP GTPase 域的侧向定位，从而指导椭圆形次生细胞壁凹陷的形成。IQD13 的缺失和过表达分别导致异常圆形和狭窄的次生细胞壁凹陷的形成。异位表达的 IQD13 通过促进微管挽救增加了平行皮质微管的存在。重建方法表明，IQD13 将活性 ROP 域的区域限制在皮质微管的晶格内，导致狭窄的 ROP 域形成。这种活性需要 IQD13 与质膜的相互作用。这些发现表明 IQD13 积极调节微管动力学及其与质膜的连接，从而协同限制活性 ROP 域的区域，导致椭圆形次生细胞壁凹陷的形成。这一发现揭示了微管-质膜连接作为侧向围栏的作用，该围栏决定 Rho GTPase 域的平面形状。
