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 disruptsfloral 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 offloral meristem termination in tomato.SlCRCa func-tions as an indispensablefloral meristem terminator by suppressing SlWUS activity through the TOMATO AGAMOUS 1(TAG1)–KNUCKLES(SlKNU)–INHIBITOR OF MERISTEM ACTIVITY(SlIMA)network.A 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 homeostasis in theflo-ral meristem,which is repressed by heat stress via the circadian factor EARLY FLOWERING 3(SlELF3).These results provide new insights intofloral meristem termination and the heat stress response inflowers and fruits of tomato and suggest that SlCRCa provides a platform for multiple protein interactions that may epigenetically abrogate stem cell activity at the transition fromfloral meristem to carpel initiation.