PIF3/HY5 module regulates <i>BBX11</i> to suppress protochlorophyllide levels in dark and promote photomorphogenesis in light

Greening of cotyledons during de-etiolation is critical for harvesting light energy and sustaining plant growth. PIF3 HY5 antagonistically regulate protochlorophyllide synthesis in the dark. However, mechanism by which PIF3/HY5 module regulates genes involved not clear. Using genetic, molecular biochemical techniques we identified that B-BOX protein BBX11 acts directly downstream to transcriptionally modulate synthesis. Dark-grown bbx11 35S:BBX11 seedlings exhibit an enhanced reduced ability green, respectively, when exposed light. Transcript levels HEMA1 CHLH are upregulated accumulate high dark undergo photobleaching upon illumination. inhibits binding its promoter. suppresses cotyledon greening defect pif3 after prolonged dark, indicating PIF3-mediated regulation dependent on BBX11. The hy5 also suppressed lines overexpressing In light, binds promoter activates expression BBX11-mediated hypocotyl inhibition. We show a opposite ways optimise accumulation promote photomorphogenesis