蒺藜苜蓿固氮共生过程中植物宿主通过调节LIN的表达控制根瘤菌侵染的机制

豆科植物可以通过与根瘤菌发生固氮共生作用来获得氮营养。固氮共生信号的传递需要根瘤发育和根瘤菌侵染通路之间的紧密协调。申请人通过突变体筛选和研究，发现在蒺藜苜蓿def1（delayed nitrogen fixation 1）突变体中，LIN（Lumpy infections）启动子区的缺失会导致根瘤菌侵染相对于根瘤发育明显滞后的表型，表明LIN的精确表达在植物宿主调控的根瘤菌侵染过程中非常重要。为解析LIN的功能及其转录调控通路，本课题将开展三方面的研究：（1）分析LIN的分子生物学功能，揭示不同突变体中LIN表达水平不同导致表型差异的分子基础；（2）高通量筛选分别与野生型或def1突变型LIN启动子区结合的转录因子，分析目标转录因子与LIN的表达调控关系；（3）阐明LIN的转录调控因子在固氮共生中的调节功能。对LIN及其转录调控机制的研究可以揭示固氮共生中植物特异调控根瘤菌侵染的机制。

Legume plants can form a symbiotic relationship with rhizobia bacteria to obtain nitrogen nutrition. The successful establishment of nitrogen fixing symbiosis requires the coordination between nodule development and rhizobium infection signaling pathways. Through mutant screen and genetic research, the applicant discovered that in Medicago truncatula def1 (delayed nitrogen fixation 1) mutant, a deletion in the promoter region of LIN (Lumpy Infections) gene would lead to the delayed rhizobia infection phenotype, indicating that the fine-regulation of LIN expression is very important in controlling rhizobia infection. To analyze the function of LIN and its expressional regulatory apparatus, this project will perform research at 3 major aspects: (1) Characterization of the molecular function of LIN, reveal the mechanism of why altered LIN expression levels in different mutants lead to phenotype variations; (2) High-throughput screen to identify transcription factors binding to LIN promoters in wild type and def1 respectively, and confirm the transcriptional-regulating relationship between LIN and respective transcription factors; (3) Utilizing gene-editing and other research tools to investigate the molecular functions of LIN-related transcription factors in nitrogen fixing symbiosis. Research into LIN and its expressional regulatory apparatus can shed light on the mechanisms of how plant hosts specifically control rhizobia infection during nitrogen fixing symbiosis.