滞绿基因STAY-GREEN在蒺藜苜蓿根瘤衰老中的功能研究

Biological nitrogen fixation can reduce the fertilizer costs and improve the soil quality in agriculture. As for legume species, unique advantage is their response to nitrogen limitation - nitrogen fixation from the soil by the formation of nodules, resulting in the symbiosis with rhizobia. Nodule senescence, which is closely related with the plant development, is considered as a very complicated but unclear process. In Medicago truncatula, nodule senescence includes developmental senescence and senescence caused by stresses. Nodule senescence caused by the various types of stress or deficient recognition between partners develops much more rapidly than developmental senescence and present features of oxidative stress and even plant cell death. On the other hand, it is believed that extending the period of active nitrogen fixation by delaying the nodule senescence might improve the ability of symbiotic nitrogen fixation and quantity of ammonium. Our previous study showed that the senescence of both plant and nodule are delayed in stay-green (mtsgr) mutant of M.truncatula. In this project, we plan to investigate the roles of MtSGR gene in the process of nodule senesence. This project not only broadens the molecular research of symbiotic nodule development and senescence regulation, but also provides the genetic evidences that there is overlap between plant and nodule development, and the new candidate genes will be provided to molecular genetic engineering of legume forages as well.

生物固氮是一个既不消耗矿质能源且对环境友好，又能减少化学氮肥用量并提高土壤肥力的有效途径，在农业和畜牧业生产中均具有重要的应用价值，并正在得到广泛的研究。共生固氮根瘤的衰老是一个与植物生长发育相关的复杂过程，目前该途径还没有被完全揭示。外界环境的胁迫能够导致根瘤的衰老快于植物发育过程中正常的器官衰老，植物无法利用根瘤间接吸收氮源，从而产生氧化胁迫甚至植株死亡。另一方面，如果根瘤衰老被推迟，植物的共生固氮过程可能会被延长，可增加其固氮能力和固氮量。我们之前的研究表明，豆科模式植物蒺藜苜蓿滞绿突变体stay-green不仅植株衰老延迟，而且根瘤衰老也延迟。本项目计划对STAY-GREEN基因在根瘤的发育及衰老过程中的功能进行系统研究。本项目可为进一步拓展共生固氮根瘤发育和衰老机制提供理论依据，同时也为豆科植物的功能基因工程改良提供了新的模式与思路。

共生固氮根瘤的衰老与植物生长发育密切相关，目前其机制仍然不清楚。在本研究中，我们利用蒺藜苜蓿stay-green (sgr)突变体研究了SGR基因在叶片和根瘤衰老中的作用。我们发现SGR基因在叶片和根瘤衰老中都起到了关键的作用。通过RNA-SEQ, Go, Mapman等分析，我们发现SGR基因在衰老之前和过程中都发挥了作用，这表明sgr突变体在诱导衰老之前其转录组和生理状态就已经和野生型有很大不同。另外，过表达SGR可导致叶片和根瘤衰老，表明其可直接诱导衰老程序启动。