A positive feedback loop formed between OsFTIP9 and OSH1 orchestrates temperature-sensitive seed germination in rice

Seed germination, critical for seedling establishment and subsequent development, is regulated by endogenous hormones and external environmental stimuli. However, the molecular mechanisms governing temperature-sensitive seed germination remain largely unclear. In this study, we identify a temperature-sensitive regulatory module controlling rice seed germination, in which FT-interacting protein 9 (OsFTIP9) promotes germination at optimal temperatures by interacting with Oryza sativa HOMEOBOX 1 (OSH1) and sequestering it in the cytosol, thereby limiting its nuclear translocation. Within the nucleus, OSH1 directly activates the expression of ABA biosynthetic genes, 9-cis-epoxycarotenoid dioxygenase 3 (OsNCED3) and OsNCED5, by facilitating chromatin loop formation. Crucially, reduced nuclear OSH1 activates OsFTIP9 expression, establishing a positive feedback loop that amplifies OsFTIP9 accumulation and promotes seed germination. Under optimal temperatures, osftip9 and OSH1 RNAi mutants exhibit altered germination compared with the wild type, whereas these differences are abolished under low temperatures. Intriguingly, low temperature impairs OsFTIP9-mediated cytosolic retention of OSH1, promoting its nuclear accumulation, ABA biosynthesis, and ABA-dependent seed dormancy. Collectively, our study identifies the OsFTIP9-OSH1 module as a temperature-sensitive molecular switch that integrates environmental cues to precisely control ABA-regulated seed dormancy and germination through reciprocal regulation and spatial sequestration, elucidating a key mechanism underlying temperature-sensitive seed germination and providing potential targets for improving germination-stage cold tolerance in rice.