大豆特有的GmPIN9d基因调控结瘤的分子机制

氮素是植物生长的必须元素，根瘤菌与豆科植物根系共生互作产生结瘤，在根瘤内将N2转换成可供植物吸收的铵态氮。前人研究证明生长素能调控大豆结瘤和固氮，但是其调控机制仍不清楚。本实验室前期研究证明生长素输出抑制剂NPA处理能显著促进大豆结瘤和提高固氮酶活性；对候选基因的表达模式分析发现大豆中特有的PIN9d基因在根部中柱鞘细胞和根瘤维管组织特异高水平表达；转基因植株验证表明，过量表达PIN9d基因显著减少结瘤数目；而PIN9d RNAi和CRISPR植株则显著增加结瘤，暗示PIN9d在中柱鞘建立和维持的生长素浓度梯度在调控结瘤过程中具有重要功能。本研究据此设计一系列遗传学、生理学和细胞生物学实验，旨在解析大豆结瘤过程中生长素活动分布规律，阐明PIN9d基因建立和维持生长素浓度梯度在调控结瘤与固氮过程中的生物学功能及分子生物学机制，以期为分子辅助及精准育种创制高效结瘤，固氮效率高的大豆新品种提供理

Nitrogen is an essential element for plant growth, the rhizobia can symbiosis with legume root and induce nodulation, the atmospheric nitrogen convert into ammonium inside bacteroids, which transported into plant and employed for its growth. Previous reports showed that auxin play critical roles in rhizobia-soybean interaction and nodulation processes, but the underlying mechanism is still an enigma. Here we showed that treatment with auxin polar transportation inhibitor displayed enhancing rhizobia-soybean interaction and increase nodulation. transcriptional profiling and histochemical analysis illustrated that the GmPIN9d is highly and specifically expressed in root pericycle and nodule vascular bundle; transgenic plant analysis showed that GmPIN9d overexpressor with less nodules, while GmPIN9d-RNAi and CRISPR Knock-out lines significantly enhanced nodule numbers; these results implicated that the PIN9d playing a pivotal roles in establishing and maintaining auxin gradient for nodulation. We therefore design a series of genetics, physiological and cytological experiments to dissect the auxin behavior during nodulation, aimed to elucidating the function and underlying mechanism of GmPIN9d in establishing and maintaining auxin gradient in pericycle promoting nodulation. This study will provide a theoretical basis for creating more nodules and higher efficiency nitrogen fixation soybean as well as soybean germplasm innovation.