Heat stress impairs floral meristem termination and fruit development by affecting the BR-SlCRCa cascade in tomato

Floral meristem termination is a key step leading to carpel initiation and fruit development. The frequent occurrence of heat stress due to global warming often disrupts floral determinacy, resulting in defective fruit formation. However, the detailed mechanism behind this phenomenon is largely unknown. Here, we identify CRABS CLAW a (SlCRCa) as a key regulator of floral meristem termination in tomato. SlCRCa functions as an indispensable floral meristem terminator by suppressing SlWUS activity through a network of TOMATO AGAMOUS 1 (TAG1)-KNUCKLES (SlKNU)- INHIBITOR OF MERISTEM ACTIVITY (SlIMA). The direct binding assay revealed that SlCRCa specifically binds to the promoter and second intron of WUSCHEL (SlWUS). We also demonstrate that SlCRCa expression depends on brassinosteroid (BR) homeostasis in the floral meristem, which is repressed by heat stress via the circadian factor EARLY FLOWERING 3 (SlELF3). Collectively, these results provide new insights into floral meristem termination and the heat stress response in flowers and fruits of tomato and suggest that SlCRCa provide a platform for multiple proteins interactions which may epigenetically abrogate stem cell activity at the transition from floral meristem to carpel initiation.