Transcriptional and Functional Insights Into the All-Stage Resistance Gene GmRmd1-Mediated Regulation of Resistance to Powdery Mildew in Soybean.

Powdery mildew disease (PMD), caused by Microsphaera diffusa, is a devastating soybean foliar disease. This study identified GmRmd1 as a candidate in Guangxi landrace MSRF (all-stage resistance to PMD) and validated it as a positive PMD resistance regulator. Hypersensitive response (HR) assays confirmed its Toll interleukin-1 receptor (TIR), nucleotide-binding site (NBS) and basic secretory protein (BSP) domains are critical for immune responses. GmRmd1 was induced by M. diffusa, and its expression was inhibited by GmWRKY27 and GmERF138 specifically binding to the W-box and GCC-box elements of the GmRmd1 promoter, respectively. RNA-Seq revealed that chromosome 16 (chr16) resistance cluster genes (Glyma.16G214100, Glyma.16G214200, Glyma.16G215100 and Glyma.16G215800) showed GmRmd1-related expression patterns. Yeast two-hybrid, bimolecular fluorescence complementation and luciferase assays demonstrated GmRmd1 interacts not only with itself, but also with GmRmd2 (Glyma.16G215100), GmRmd3 (Glyma.16G214900) and GmRnl1 (NLR cofactor). In addition, mutants of GmRmd3 and GmRnl1 are more susceptible to M. diffusa. Notably, GmRmd1 enhances the resistance of PMD by interacting with GmPER1 (lignin synthesis-related) and increasing the synthesis of lignin. Genomic analysis indicated that the number of soybean accessions carrying the GmRmd1 locus gradually decreases from north to south and from west to east in China. Taken together, GmRmd1 forms functional protein complexes with GmRmd2, GmRmd3, and GmRnl1 to regulate lignin biosynthesis and thereby modulate disease resistance. These insights provide novel perspectives into the molecular mechanisms of GmRmd1-mediated resistance to soybean PMD.