Un bucle de retroalimentación positiva formado entre OsFTIP9 y OSH1 orquesta la germinación de semillas de arroz...

Seed germination, critical for seedling establishment and subsequent development, is regulated by endogenous hormones and external environment 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, wherein FT-interacting protein 9 (OsFTIP9) promotes seed germination under optimal temperature by interacting with Oryza sativa HOMEOBOX 1 (OSH1) and sequestering it in the cytosol, thus 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 temperature. 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.