MS2/GmAMS1 encodes a bHLH transcription factor important for tapetum degeneration in soybean.

key messageGmAMS1 is the only functional AMS and works with GmTDF1-1 and GmMS3 to orchestrate the tapetum degeneration in soybean. Heterosis could significantly increase the production of major crops as well as soybean [Glycine max (L.) Merr.]. Stable male-sterile/female-fertile mutants including ms2 are useful resources to apply in soybean hybrid production. Here, we identified the detailed mutated sites of two classic mutants ms2 (Eldorado) and ms2 (Ames) in MS2/GmAMS1 via the high-throughput sequencing method. Subsequently, we verified that GmAMS1, a bHLH transcription factor, is the only functional AMS member in soybean through the complementary experiment in Arabidopsis; and elucidated the dysfunction of its homolog GmAMS2 is caused by the premature stop codon in the gene's coding sequence. Further qRT-PCR analysis and protein-protein interaction assays indicated GmAMS1 is required for expressing downstream members in the putative DYT1-TDF1-AMS-MYB80/MYB103/MS188-MS1 cascade module, and might regulate the upstream members in a feedback mechanism. GmAMS1 could interact with GmTDF1-1 and GmMS3 via different region, which contributes to dissect the mechanism in the tapetum degeneration process. Additionally, as a core member in the conserved cascade module controlling the tapetum development and degeneration, AMS is conservatively present in all land plant lineages, implying that AMS-mediated signaling pathway has been established before land plants diverged, which provides further insight into the tapetal evolution.