生长素受体MtTIR1调控植物耐寒性功能分析

Cold stress restricts plant growth, development and distribution in nature, and improving cold tolerance of crops is one of the important breeding targets. Auxin signaling involves in cold signaling pathway to regulate cold tolerance, but the roles and mechanisms of auxin signaling in plant cold tolerance remain unclear. Our previous research indicates that the transcription levels of auxin receptor gene MtTIR1 in Medicago truncatula, MfTIR1 in Medicago falcata, and MsTIR1 in Medicago sativa were all decreased significantly under low temperature, and the expression level of TIR1 was negatively correlated with cold tolerance of plant. In this study, Medicago truncatula will be used as the experimental material. We try to investigate the roles of MtTIR1 in cold tolerance by constructing overexpression and knock-out mutants, screen and identify MtAuxs/MtIAAs interaction with MtTIR1 and its roles in plant cold tolerance, analyze the expression level of marker genes of cold signaling in mutants and overexpressed plants of MtTIR1 and MtAuxs/MtIAAs. Finally, we aim to elucidate the molecular mechanisms underlying MtTIR1 regulating cold tolerance in Medicago truncatula. Consequently, this project will provide a theoretical basis for development of plant with increased cold tolerance in alfalfa and other crops.

低温胁迫限制植物的生长发育和自然分布，提高作物耐寒性是重要的育种目标之一，研究表明生长素调控信号的变化与耐寒性相关，但其功能及机制尚不清楚。我们研究发现生长素受体基因TIR1在蒺藜苜蓿、黄花苜蓿和紫花苜蓿中均受低温诱导显著下调表达，且与苜蓿耐寒性负相关，表明TIR1可能负调控苜蓿耐寒性。本项目拟以蒺藜苜蓿为研究材料，利用分子生物学、遗传学和生理生化等手段，构建MtTIR1过表达和敲除突变体，明确MtTIR1对蒺藜苜蓿耐寒性调控作用；筛选鉴定与MtTIR1互作的MtAuxs/MtIAAs及其对耐寒性的调控功能；分析MtTIR1、MtAuxs/MtIAAs突变体及过表达株系材料中低温响应标记基因的相对表达量。最终阐明MtTIR1调控蒺藜苜蓿耐寒性功能及分子机制，为苜蓿及其他作物耐寒性遗传改良提供理论基础。

低温胁迫是影响植物生长发育的重要因素之一，而植物在进化过程中形成了复杂的低温适应性机制。关于生长素与植物低温胁迫响应的关系，有研究表明低温主要是影响了生长素的运输而不是生长素信号，但是低温胁迫可引起大部分生长素信号通路相关基因的表达变化，生长素信号可能与低温信号互作共同调控植物低温适应性。生长素受体 TIR1 是生长素信号通路上的核心元件，本项目从MtTIR1基因入手，以蒺藜苜蓿为研究材料，利用生物信息学、分子生物学、遗传学和生理生化等手段，证明了生长素受体 MtTIR1 可以负调控蒺藜苜蓿耐寒性，并筛选鉴定到2个下游与 MtTIR1 互作的生长素信号因子MtIAA4和MtIAA7，并发现MtIAA4的过量表达可以提高植物的耐寒性。且MtTIR1和MtIAA4对耐寒性的调控均依赖于CBF途径。本研究首次阐明了生长素信号通过MtTIR1-MtIAA4协同CBF信号途径调控蒺藜苜蓿低温适应性机制。研究结果有助于了解生长素信号参与调控植物低温适应性分子途径，为苜蓿及其他作物耐寒性遗传改良提供理论依据。