The RLI1-OsPUB77-OsBZR3 module mediates the crosstalk between phosphate starvation and brassinosteroid signaling pathways to shape rice shoot architecture.

Abstract

Plant architecture is a critical agronomic trait directly affecting planting density and crop yield. Phosphate starvation in rice (Oryza sativa) leads to a significant reduction in tiller number and a more upright leaf angle. Insensitivity to brassinosteroid (BR) signalling can lead to similar phenotypes. However, the underlying molecular mechanism of phosphate affecting plant architecture through brassinosteroid signalling remains obscure. Here, we demonstrate that the phosphate signalling-related transcription factor RLI1a releases its repression of the novel E3 ligase OsPUB77 gene under phosphate deficiency (Pi deficiency). The accumulated OsPUB77 mediates plant architecture by ubiquitinating OsBZR3 to inhibit BR signaling. Furthermore, 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. Our findings reveal the RLI1a-OsPUB77-OsBZR3 module between Pi and BR that modulates plant architecture in response to Pi starvation in rice.