论文题目：An isoflavone reductase-like protein MtIFL negatively regulates nodule symbiosis in Medicago truncatula
论文作者：Yongrui Shen, Yan Yan, Ting Yin, Hongyu Zhang, Haijing Zhu, Siyu Zhang, Haiqing Hu, Gehong Wei* and Minxia Chou*
论文摘要：
Flavonoids are valuable metabolites produced by legumes, including Medicago truncatula , and play crucial roles in signaling communication during legume- rhizobium symbiosis. Isoflavone reductase proteins (IFRs) are involved in the biosynthesis of isoflavones and plant defense regulation. However, their role in symbiotic nitrogen fixation remains mostly elusive.
Here, 13 putative IFR gene family members were identified, and an IFR -like gene named MtIFL was functionally characterized through expression patterns, phenotypic characterizations, flavonoid metabolome, and transcriptome analyses. Furthermore,the binding partner of MtIFL was investigated using Y1H, EMSA, and Dual-LUC assays. MtIFL was strongly induced in the process of nodule development and expressed in the meristem and infection zone of mature nodules. Knockout of MtIFL promoted nodulation, while overexpression of MtIFL induced premature senescence of nodules. Further investigations revealed that MtIFL negatively regulates nitrogen-fixing symbiosis by mediating isoflavone metabolism, and MtNIN regulates MtIFL expression by binding to the hNRE motif.
Overall, our findings suggest that MtIFL negatively regulates nodule formation, thereby influencing the survival of rhizobia in nodule cells. MtNIN regulates MtIFL expression and may play a role in isoflavone metabolism. These results provide novel insights into the function of IFRs in symbiotic nodulation and the role of flavonoids in nodule development.
黄酮类化合物在豆科植物-根瘤菌共生信号交流过程中起着至关重要的作用。异黄酮还原酶蛋白（IFRs）主要参与了异黄酮的生物合成和植物防御调控。然而，它们在共生固氮中的作用机制尚不完全清晰。本研究在豆科模式植物蒺藜苜蓿中共鉴定了13个IFR基因家族成员。首先通过时空表达模式、植株与根瘤表型特征、黄酮代谢组及转录组分析对关键 MtIFL 进行了功能表征，随后通过Y1H、EMSA和Dual-LUC试验探究了 MtIFL 的上游调控机制。结果表明， MtIFL 在根瘤发育过程中被强烈诱导，主要在成熟根瘤的分生组织和侵染区表达。 MtIFL 的敲除能够促进植株结瘤，而过表达 MtIFL 导致了根瘤的过早衰老。进一步的研究证实，转录因子MtNIN通过与hNRE基序结合负调控了 MtIFL 的表达。 MtIFL 主要通过介导异黄酮代谢从而负调控共生固氮进程。抗菌试验证实，关键代谢物vestitol 能够抑制苜蓿中华根瘤菌 Sinorhizobium meliloti 1021的生长，表明 MtIFL 可能通过影响根瘤菌在根瘤细胞中的存活来负调控根瘤形成。该研究为阐明IFR在共生结瘤中的作用机制以及黄酮类化合物在根瘤发育中的潜在功能提供了新的见解。
论文链接：https://doi.org/10.1111/nph.70251