Lei Lei, Li Shundai, Du Juan, Bashline Logan, Gu Ying
Department of Biochemistry and Molecular Biology, Pensylvania State University, University Park, Pensylvania 16802.
Plant Cell. 2013 Dec;25(12):4912-23. doi: 10.1105/tpc.113.116715. Epub 2013 Dec 24.
Anisotropic plant cell growth depends on the coordination between the orientation of cortical microtubules and the orientation of nascent cellulose microfibrils. Cellulose synthase interactive1 (CSI1) is a key scaffold protein that guides primary cellulose synthase complexes (CSCs) along cortical microtubules during cellulose biosynthesis. Here, we investigated the function of the CSI1-like protein, CSI3, in Arabidopsis thaliana. Similar to CSI1, CSI3 associates with primary CSCs in vitro, colocalizes with CSCs in vivo, and exhibits the same plasma membrane localization and bidirectional motility as CSI1. However, ProCSI1:GFP-CSI3 cannot complement the anisotropic cell growth defect in csi1 mutants, suggesting that CSI3 is not functionally equivalent to CSI1. Also, the colocalization ratio between CSI1 and CSI3 is low, which may suggest heterogeneity within the CSC population. csi1 csi3 double mutants showed an enhanced cell expansion defect as well as an additive reduction of CSC velocities, and CSI3 dynamics are dependent on CSI1 function. We propose that CSI3 is an important regulator of plant cellulose biosynthesis and plant anisotropic cell growth that modulates the velocity of CSCs in both a microtubule-dependent and microtubule-independent manner.
各向异性的植物细胞生长取决于皮层微管的方向与新生纤维素微纤丝方向之间的协调。纤维素合酶相互作用蛋白1（CSI1）是一种关键的支架蛋白，在纤维素生物合成过程中引导初级纤维素合酶复合体（CSC）沿着皮层微管移动。在此，我们研究了拟南芥中类CSI1蛋白CSI3的功能。与CSI1相似，CSI3在体外与初级CSC结合，在体内与CSC共定位，并且与CSI1表现出相同的质膜定位和双向运动性。然而，ProCSI1:GFP-CSI3不能弥补csi1突变体中各向异性细胞生长缺陷，这表明CSI3在功能上不等同于CSI1。此外，CSI1与CSI3之间的共定位率较低，这可能表明CSC群体内部存在异质性。csi1 csi3双突变体表现出增强的细胞扩张缺陷以及CSC速度的累加性降低，并且CSI3的动态变化依赖于CSI1的功能。我们提出，CSI3是植物纤维素生物合成和植物各向异性细胞生长的重要调节因子，它以微管依赖和微管非依赖的方式调节CSC的速度。
