Precise control of volatile glucosylation in tea plants by CBF4, WRKY4, and an atypical bHLH transcription factor

Low temperatures impose a significant threat to plant development. Plants counteract cold stress through UDP-glycosyltransferase (UGT)-mediated glycosylation. Although nerolidol, a widely distributed phytohormone-like compound, participates in cold acclimation and interplant signaling, its regulation remains elusive. Here, we demonstrated that ATBS1-Interacting Factor 3 (CsAIF3), an atypical basic helix-loop-helix (bHLH) transcription factor lacking DNA-binding activity, activates CsUGT91Q2 expression to promote nerolidol glucoside accumulation and cold tolerance in tea plants (Camellia sinensis). Furthermore, we determined that C-repeat Binding Factor 4 (CsCBF4), a cold-responsive transcription factor, binds to the CsAIF3 promoter. In vitro and in vivo experiments confirmed that CsCBF4-CsAIF3-CsUGT91Q2 form a cascade pathway and positively regulate the cold tolerance of tea plants. Under ambient conditions, CsWRKY4 suppressed CsUGT91Q2 expression by interacting with CsAIF3, whereas under cold stress, the cold-inducible CsCBF5 competitively displaced CsWRKY4 from the CsAIF3 complex, thereby relieving transcriptional repression on CsUGT91Q2, leading to increased nerolidol glycoside accumulation and cold tolerance in tea plants. These results not only unveil noncanonical functions for DNA-binding-deficient bHLHs but also provide critical insight into how plants precisely control specialized metabolism to cope with temperature changes.