The F-box protein SHORT PRIMARY ROOT modulates primary root meristem activity by targeting SEUSS-LIKE protein for degradation in rice

Root meristem activity is essential for root morphogenesis and adaptation,but the molecular mechanism regulating root meristem activity is not fully understood.Here,we identify an F-box family E3 ubiquitin ligase named SHORT PRIMARY ROOT(SHPR) that regulates primary root(PR)meristem activity and cell proliferation in rice.SHPR loss-of-function mutations impair PR elongation in rice.SHPR is involved in the formation of an SCF complex with the Oryza sativa SKP1-like protein OSK1/20.We show that SHPR interacts with Oryza sativa SEUSS-LIKE(OsSLK) in the nucleus and is required for OsSLK polyubiquitination and degradation by the ubiquitin 26S-proteasome system(UPS).Transgenic plants overexpressing OsSLK display a shorter PR phenotype,which is similar to the SHPR loss-of-function mutants.Genetic analysis suggests that SHPR promotes PR elongation in an OsSLK-dependent manner.Collectively,our study establishes SHPR as an E3 ubiquitin ligase that targets OsSLK for degradation,and uncovers a protein ubiquitination pathway as a mechanism for modulating root meristem activity in rice.