Tissue-Specific Ubiquitination by IPA1 INTERACTING PROTEIN1 Modulates IPA1 Protein Levels to Regulate Plant Architecture in Rice

Plant architecture, a collection of genetically controlled agronomic traits, is one of the decisive factors that determine grain production. IDEAL PLANT ARCHITECTURE1 ( IPA1 ) encodes a key transcription factor with pleiotropic effects on regulating plant architecture in rice ( Oryza sativa ), and IPA1 expression is controlled at the posttranscriptional level by microRNA156 and microRNA529. Here, we report the identification and characterization of IPA1 INTERACTING PROTEIN1 (IPI1), a RING-finger E3 ligase that can interact with IPA1 in the nucleus. IPI1 promotes the degradation of IPA1 in panicles, while it stabilizes IPA1 in shoot apexes. Consistent with these findings, the ipi1 loss-of-function mutants showed markedly altered plant architecture, including more tillers, enlarged panicles, and increased yield per plant. Moreover, IPI1 could ubiquitinate the IPA1-mediated complex with different polyubiquitin chains, adding K48-linked polyubiquitin chains in panicles and K63-linked polyubiquitin chains in the shoot apex. These results demonstrate that IPI1 affects plant architecture through precisely tuning IPA1 protein levels in different tissues in rice and provide new insight into the tissue-specific regulation of plant architecture and important genetic resources for molecular breeding.