RsOBP2a, a member of OBF BINDING PROTEIN transcription factors, inhibits two chlorophyll degradation genes in green radish

The green radish (Raphanus sativus L.) contains abundant chlorophyll (Chl). DOF-type transcription factor OBF BINDING PROTEIN (OBP) plays crucial functions in plant growth, development, maturation and responses to various abiotic stresses. However, the metabolism by which OBP transcription factors regulate light-induced Chl metabolism in green radish is not well understood. In this study, six OBP genes were identified from the radish genome, distributed unevenly across five chromosomes. Among these genes, RsOBP2a showed significantly higher expression in the green flesh compared to the white flesh of green radish. Analysis of promoter elements suggested that RsOBPs might be involved in stress responses, particularly in light-related processes. Overexpression of RsOBP2a led to increase Chl levels in cotyledons and adventitious roots of radish, while silencing RsOBP2a expression through TYMV-induced gene silencing accelerated leaf senescence. Further investigations revealed that RsOBP2a was localized in the nucleus and served as a transcriptional repressor. RsOBP2a was induced by light and directly suppressed the expression of STAYGREEN (SGR) and RED CHLOROPHYLL CATABOLITE REDUCTASE (RCCR), thereby delaying senescence in radish. Overall, a novel regulatory model involving RsOBP2a, RsSGR, and RsRCCR was proposed to govern Chl metabolism in response to light, offering insights for the enhancement of green radish germplasm.