Strictosidine Synthase-like Gene NMS1 Is Required for Male Fertility in Rice by Regulating Tapetal Degradation

Background: Male sterility is a critical trait for large-scale hybrid rice seed production, yet the genetic and molecular regulatory networks governing tapetal degradation during anther development remain incompletely understood. This study aimed to clone the causal gene underlying a novel rice non-pollen male sterility mutant and elucidate its role in tapetal development and microsporogenesis. Methods: The nms1 (non-pollen male sterility 1) sterile mutant was screened from the ethyl methanesulfonate (EMS)-mutagenized progeny of the elite indica restorer line Shuhui 498 (R498). Map-based cloning and whole-genome resequencing-assisted bulked segregant analysis were used to identify the causal variant. Gene function was verified via cytological observation, genetic complementation testing, RNA sequencing, and quantitative real-time PCR (qRT-PCR) to profile sterility-associated transcriptional changes. Results: Gene mapping identified a T635A single-nucleotide substitution within OsR498G0305626400.01 on chromosome 3, which encodes a strictosidine synthase-like protein. This nucleotide alteration causes a Val212Glu amino acid change and is associated with delayed tapetal degradation and pollen abortion. Transgenic complementation experiments verified that functional NMS1 restores fertility in nms1 mutant plants. Spatiotemporal expression analysis showed predominant NMS1 expression in late-developing spikelets. Furthermore, combined RNA sequencing and qRT-PCR analyses demonstrated that loss of NMS1 function leads to significant transcriptional dysregulation of key regulators of programmed cell death (PCD) in the tapetum (PTC2, TIP2) and pollen wall biosynthesis genes (TIP3, OsMS2). Conclusions: This study demonstrates that NMS1 plays a crucial role in coordinating tapetal degradation and microspore development in rice. The discovered functional SNP of NMS1 provides a novel theoretical foundation and a valuable sterile genetic resource for hybrid rice breeding.