The RLI1-OsPUB77-OsBZR3 module mediates the crosstalk between phosphate starvation and brassinosteroid signaling...

Plant architecture is a critical agronomic trait directly affecting planting density and crop yield. Phosphate (Pi) starvation in rice (Oryza sativa) leads to a significant reduction in tiller number and a more upright leaf angle. Insensitivity to brassinosteroid (BR) signaling can lead to similar phenotypes. However, the molecular mechanisms underlying how Pi affects plant architecture through brassinosteroid signaling remain obscure. In this study, we demonstrate that the Pi starvation-induced E3 ligase OsPUB77 regulates rice shoot architecture by affecting leaf angle and tiller number. We further revealed that the Pi-signaling-related transcription factor RLI1a releases its repression of the expression of OsPUB77 under Pi deficiency. Subsequently, the accumulated OsPUB77 influences shoot architecture by ubiquitinating OsBZR3 to inhibit BR signaling. Furthermore, we found that natural variation in two single-nucleotide polymorphisms within the OsPUB77 U-box domain coding OsPUB77^R530 results in higher ubiquitin transfer activity than OsPUB77^I530 due to a stronger interaction with E2. Introducing the OsPUB77pro::OsPUB77^R530I transgene into the ospub77-1 background confirmed that OsPUB77^R530 results in more upright leaves. Collectively, our work identifies an RLI1a-OsPUB77-OsBZR3 module that mediates the crosstalk between Pi and BR signaling to shape shoot architecture in response to Pi starvation in rice.