Abstract

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.