Thermo-sensitive tasiRNA biogenesis integrates temperature signals to maintain spikelet patterning in rice

Rising temperatures threaten crop yields by disrupting panicle and spikelet development, yet the molecular sensors of thermal stress remain unknown. Through a field-based ethyl methanesulfonate (EMS) screen, we identified two rice mutants, tspd2 and tspd3, that show dramatic temperature-sensitive defects in spikelet polarity. Genetic mapping revealed lesions in two core small RNA (sRNA) factors: a weak OsDCL4 allele in tspd2 and a splice-site mutation in OsDRB4 in tspd3. We show that OsDRB4 is a dual-localized dsRNA-binding protein that directly binds TAS3 precursor RNAs and forms a functional complex with OsDCL4 to produce 21-nt phasiRNAs. Loss of OsDRB4 causes a temperature-exacerbated collapse of 21-nt phasiRNAs, including TAS3-derived tasiRNAs, leading to heat-induced derepression of OsARF3 genes. Strikingly, knockout of OsARF3 largely restores normal spikelet morphology, demonstrating that OsARF3 dysregulation is the proximal cause of thermo-sensitive spikelet defects. Our findings uncover a previously hidden mechanism in which an OsDCL4-OsDRB4-tasiRNA-OsARF3 axis buffers spikelet development against temperature fluctuations. This work establishes sRNA biogenesis as a critical determinant of thermal resilience in rice reproduction, providing a molecular entry point for engineering climate-resilient crops.