ABA和干旱敏感突变体abo11的基因克隆与功能分析

Drought stress is an important phenomena which limits production and yield of crop. Plant phytohormone abscisic acid(ABA) plays a key role in plant responses to drought stress. An ABA signaling pathway in guard cell has been reported several years ago. ABA receptor PYR1/PYL/RCARs can interact with protein phosphatase 2C (PP2C) directly when binding to ABA, and inhibit the phosphatase activition. Then PP2C relieves the inhibition of protein kinase OST1 and GHR1, which in turn can phosphorylate SLAC1 to close the stomatal pores. ABA can inhibit the seed germination and primary root growth also. However, some components in the ABA and drought stress signaling pathway are poorly known. The ABA-sensitive mutant abo11 was isolated using the ABA-mediated inhibition of primary root growth phenotype. abo11 is sensitive for drought stress and induces late flowering. We hypothesized ABO11 was a gene/new gene with an new function when ABO11 was mapped to 5 BACs in the bottom of chromosome 1. We plan to map the gene of ABO11 continusely and analyse the function of ABO11 in ABA and drought stress signaling pathway. We hope to find a new gene in ABA and drought stress signaling pathway, which can help us understand the pathway better and provide a valuable gene for crop drought-tolerant breeding by gene engineering.

干旱是影响农作物产量和分布的重要因素，植物激素脱落酸(ABA)在植物适应干旱胁迫过程中起重要作用。植物受到干旱胁迫时，体内ABA含量升高，受体PYR1/PYL/RCARs结合ABA，同时招募PP2C形成复合体，解除对蛋白激酶OST1、GHR1等的抑制，使后者通过磷酸化激活SLAC1的通道活性，诱导气孔关闭，以适应干旱胁迫。ABA还抑制植物的种子萌发、主根生长等过程。利用ABA抑制主根生长的表型，筛选获得一株对ABA敏感的拟南芥突变体abo11，abo11对干旱胁迫也敏感，具有晚花的表型，已将ABO11定位于5个BAC内，并初步确定是一个具有新功能的基因。计划继续克隆ABO11基因，并通过生理、分子和生化等揭示该基因在ABA、干旱胁迫中的功能。期望本研究能发现一个新的对ABA、干旱胁迫敏感的基因，有助于更好的理解植物适应干旱胁迫的机理，为基因工程培育农作物抗旱新品种提供有价值的功能基因。

植物激素ABA可以调节植物种子萌发、根的生长和对干旱胁迫的响应，从拟南芥突变体库中，筛选获得一个主根生长对ABA敏感的突变体abo11，表现为种子萌发对ABA、H2O2（ROS）敏感，说明ABO11可能通过调节下游的ROS信号参与ABA的调控过程。利用图位克隆，将ABO11定位于1号染色体的末端，进一步定位发现是一个编码锚定于膜上的泛素折叠蛋白5前体的基因MUB5的第40位的碱基G突变为A，导致一个高度保守的丙氨酸残基突变为苏氨酸残基。利用qRT-PCR检测发现，ABO11/MUB5基因在茎、花中表达量最高，在根和叶片中的表达量相对较低；利用MUB5-GFP融合蛋白证明MUB5在细胞的膜系统中都有定位。通过土壤中直接干旱处理及离体叶片失水实验，证明abo11具有干旱敏感的表型，在干旱胁迫下，该基因的表达量也发生变化。利用ABA、NaCl、甘露醇和高温等条件处理，MUB5的基因表达水平发生改变，说明该基因参与多个胁迫信号。通过该研究，发现了植物ABA信号通路中一个新的基因，有助于理解植物ABA信号及干旱胁迫信号的转导机制。