蒺藜苜蓿MtHB2/HOX27转录因子抗逆调节机理研究

Medicago truncatula has emerged as a model plant for legume genetics and genomics because it is diploid with relatively small genome (450-550Mb), self-fertile, relatively easy to transform, and whole genome sequenced after Arabidopsis and rice. It is widely used in international research on molecular mechanism of development and stress response of leguminous plants, more and more attention is also given to domestic related area research. Plant development is adapted to changing environmental conditions for optimizing growth. This developmental adaptation is in?uenced by signals from the environment, which act as stimuli and may include submergence and ?uctuations in water status, light conditions, nutrient status, temperature and the concentrations of toxic compounds. Transcription factor (TFs) networks regulate these plant growth adaptation responses through integration of developmental and environmental cues. TFs of homeodomain-leucine zipper (HD-Zip) families contribute to the plasticity of plant growth and are responsible for modulating plant development in response to environmental stimuli. In the previous study, we identified a M.truncatula gene, MtHB2/HOX27, encoding a putative transcriptional factor. The expression of MtHB2/HOX27 is induced by cold,drought and salt stress.The plants of MtHB2/HOX27 transgenic Arabidopsis is less tolerant to abiotic stress than Wild-type plants. Based on these results,the proposed project aims to functionally characterize of MtHB2/HOX27 by generating mutants and transgenic M. truncatula with altered expression of MtHB2/HOX27, and dissect the molecular mechanism and signaling network associated with MtHB2/HOX27 in response to enviromental adaptation. The outcome of the project will advance our knolwedge on the function of HD-Zip II and its regulatory network in terms of its role in response to abiotic stress and enviromental adaptation.

蒺藜苜蓿是继拟南芥和水稻之后完成基因组测序的重要豆科模式植物，国际上广泛应用于研究豆科植物发育和抗逆的分子机理，国内相关研究也正在兴起。植物在生长发育过程中会频繁遭受水分、温度和盐碱等逆境胁迫，制约其生长。转录因子在植物逆境胁迫应答中起重要的调控作用。同源异型盒蛋白是一类含有高度保守同源异型域的转录因子，参与调控植物的多个生物学过程。通过干旱差减文库和低温芯片杂交，申请人筛选到一个对干旱、低温和盐响应的同源异型盒家族基因MtHB2/HOX27。在拟南芥中的异源表达研究发现，该基因调节拟南芥的逆境胁迫抗性。本项目拟在此基础上，通过超表达和沉默该基因，研究它在苜蓿逆境胁迫应答中的功能，揭示该基因调节抗逆的分子机理，解析其在植物逆境胁迫应答中的调控网络。研究结果对于揭示同源异型盒蛋白的抗逆分子机理具有重要科学意义, 为利用苜蓿抗性基因资源提供理论支持，将推动我国豆科植物抗逆分子机理的研究。

蒺藜苜蓿是继拟南芥和水稻之后，完成基因组测序的重要豆科模式植物，广泛应用于研究豆科植物发育和抗逆的分子机理。逆境是植物面临的主要环境胁迫因子，能够对植物造成伤害，甚至导致植物死亡。转录因子、植物激素、非编码RNA等在植物逆境胁迫应答中起重要的调控作用。本研究发现，同源异型盒家族基因MtHB2/HOX27具有干旱、低温和盐胁迫响应特性，调节植物根形态建成，影响植物对逆境胁迫的抗性。MtHB2/HOX27转基因拟南芥根形态发生显著改变，表现为主根短，侧根发育受抑制。研究发现MtHB2/HOX27基因的表达受生长素快速诱导，MtHB2/HOX27转基因拟南芥对外源生长素和生长素运输抑制剂的敏感性与野生型不同， MtHB2/HOX27基因超表达株系中，生长素输出载体蛋白PIN1、PIN3、PIN7及DR5的表达降低，以及基因表达谱分析中转基因植株中许多生长素相关的应答基因被下调，说明MtHB2/HOX27负调控转基因植株根中生长素的运输和积累。此外，利用发根农杆菌转化蒺藜苜蓿，得到35S: MtHB2/HOX27嵌合体植株，其侧根发育也表现出明显受抑制的表型，进一步证明了MtHB2/HOX27在苜蓿根生长发育中的重要作用。MtHB2/HOX27转基因植物主根短、侧根数少、密度低等特性可能是影响其抗性的形态基础。MTR4g070320是影响MtHB2/HOX27基因表达的上游基因。在MTR4g070320插入突变体中，MtHB2/HOX27基因的表达下调了近70%。超表达株系中，MtHB2/HOX27基因的表达上调了2倍左右。MTR4g070320基因超表达株系低温胁迫抗性降低，从另一方面验证了MtHB2/HOX27基因对植物低温冷冻抗性的负调控作用。乙烯是一种结构最简单的植物激素，参与调节植物对多种胁迫的响应。本研究发现，低温驯化抑制乙烯信号传导关键因子MtSKL1表达，导致MtEIN3和MtEIN3/EIL1及其下游的MtERFs基因表达下调，最终上调MtCBF1-3和MtCAS15来提高蒺藜苜蓿的抗冻性。逆境胁迫响应非编码RNA的鉴定和功能研究说明，植物对逆境胁迫响应调控的多层次性。