OsMDS1 regulates cell elongation and thermotolerance in rice.

Cereal crops often exhibit a tradeoff between thermotolerance, which is important for climate adaptation, and cell elongation, which is crucial for ideal plant architecture and yield. Here, we characterize the rice mutant with dwarfing and short roots/grains 1 (Osmds1), which shows dwarfism, shorter roots, and reduced grain size, along with enhanced thermosensitivity. OsMDS1 encodes a KNOTTED1-like homeobox (KNOX) transcription factor. A 15-bp deletion in the GSE domain of OsMDS1 is identified in Osmds1, which we show to be an allele of Osh15, d6, Oskn3, Shennong9816d, and rlb. OsMDS1 interacts with the chaperone LO9-177 and the transcription factor OsBC1, two components of the OsBUL1-LO9-177-OsBC1 complex, but not with OsBUL1, whereas Osmds1 binds to all three components. Further analysis indicates that OsMDS1 and OsBC1 synergistically activate the auxin biosynthesis genes OsYUCCA1 and OsTDD1, revealing a link between the KNOX and auxin pathways. OsMDS1 also interacts with the heat-shock protein OsDjC38 and regulates its expression. Genetic analysis shows that Osmds1 and OsDjC38 knockout plants have elevated sensitivity to prolonged heat stress and impaired antioxidant enzyme activity. Our results suggest that OsMDS1 coordinates both cell elongation and the heat-stress response, possibly through auxin pathways, providing a promising target for rice breeding.