γ-Aminobutyric Acid Alleviates Discoloration of Or Mutant Cauliflower via BoMYB24-Mediated Transcriptional Regulation of BoLCYB

Abstract Orange (Or) mutant cauliflower is prone to discoloration during storage, which affects its commercial value. γ-Aminobutyric acid (GABA) treatment can effectively delay the discoloration of Or mutant cauliflower during storage; however, its mechanism of action remains unclear. Here, we aimed to identify key genes and candidate transcription factors associated with discoloration in Or cauliflower treated with GABA during storage. Transcriptome analysis revealed that GABA regulated BoLCYB, with BoMYB24 identified as the candidate transcription factor in this pathway. BoMYB24 binds the BoLCYB promoter through the MBS-1 motif. Additionally, under GABA treatment, the transcriptional activation effect of BoMYB24 on BoLCYB is further enhanced. BoMYB24 overexpression increases BoLCYB expression, leading to a large accumulation of β-carotene in chromoplasts and promoting the accumulation of auxin and abscisic acid. Furthermore, under GABA treatment, the transcription level of BoMYB24 was markedly upregulated, thus delaying the postharvest discoloration of Or mutant cauliflower by positively regulating BoLCYB.