脱落酸调控植物根分生区细胞分裂与分化的分子机理

Abscisic acid (ABA) is a classic phytohormone that plays crucial roles in seed dormancy, seed germination, plant growth and development, lotus nodulation and plant disease resistance. ABA is accumulated quickly under abiotic stress conditions such as drought stress, and regulates the stomatal movement and the expression of stress inducible genes, reduces the water transpiration and increases plant drought resistance. Right now a lot of studies have been focused on ABA biosynthesis and transporting, stomatal movement and controlling gene expression. However, how ABA regulates root growth is barely explored. Root is critcal for plants to get enough water under drought stress. Root meristem activity is regulated by different phytohormones mainly as a consequence of their effects on a key auxin repressor, SHORT HYPOCOTYL2 (SHY2/IAA3). Here we plan to use different root ABA sensitive mutants to dissect the ABA-regulated cell division and differentiation in the root meristem, to find the relationship between ABA and auxin signaling components. Our study will provide new information and new genes for improving crop drought tolerance and crop yield .

脱落酸（ABA）是一种传统逆境激素，在调节种子休眠、种子萌发、植物的生长发育、豆科植物固氮以及植物抗病性等发挥重要功能。ABA在非生物逆境如干旱下迅速积累，调控气孔运动、基因表达，降低水分蒸腾，提高植物的抗旱性。目前在ABA合成、运输，ABA调控气孔运动以及对逆境诱导蛋白等的研究较多，对ABA如何调控根的生长的研究较少。根对植物在干旱条件获取水分至关重要。根的生长主要由根分生区细胞的分裂与分化的协同调控决定的。对根生长的研究主要集中在生长素及细胞分裂素协同调控SHY2/IAA3的研究上。我们在植物激素重大研究计划的支持下，初步发现ABA调控根的生长主要通过调控生长素信号传导完成的。本项目计划通过对不同ABA敏感突变体的解析，剖析ABA信号途径与生长素信号途径的交互传递机制，揭示ABA调控根分生区细胞分裂和分化的分子机制。

活性氧在调节植物生长发育中起信号分子的作用，但具体分子作用机理尚不清楚。利用正向遗传学筛选ABA敏感的突变体，克隆得到了ABO8 (ABA-overly sensitive 8)基因。abo8突变体无论是根的生长以及种子的萌发都对ABA非常敏感，表明ABO8是响应ABA过程的关键因子。ABO8编码拟南芥一个PPR (pentatricopeptide repeat)蛋白，其定位在线粒体，主要在主根尖、侧根尖和侧根原基中大量表达。ABO8负责线粒体电子传递链复合体I nad4亚基mRNA的第三个内含子的剪接。ABO8突变引起nad4基因mRNA的剪切紊乱，使电子传递链复合体I的活性异常，进而导致的线粒体功能紊乱。由于线粒体呼吸链产生的活性氧（ROS）构成了生物体内最大数量的ROS的来源，因此ABO8突变引起线粒体功能紊乱导致abo8突变体的根尖与野生型相比积累了较多ROS。这种高水平的活性氧积累导致了根尖生长素的积累或信号水平下降，ABA和活性氧可能通过降低PLT基因的表达抑制根尖分生组织的活性。这些结果表明，ABA诱导活性氧的产生并通过调控根尖生长素的应答以及PLT的表达调节根尖分生组织的活性，进而调控植物根的生长和发育。