Functional characterization of FLC-like in relation to flower bud development of Prunus mume

We previously identified a MADS-box transcription factor gene, FLOWERING LOCUS C-like ( PmFLC-like ), a homolog of the Arabidopsis vernalization regulator FLC , which is highly expressed in Prunus mume flower buds during autumn and winter. PmFLC-like is conserved as a single-copy gene across several Prunus fruit tree species, suggesting its significant role in winter flower buds, where buds continue to develop slowly while blooming is inhibited even under forcing conditions; however, its physiological and molecular functions remain poorly characterized. In this study, molecular and physiological analyses of transgenic Arabidopsis overexpressing PmFLC-like and Japanese apricot ( P. mume ) cultivars with contrasting blooming dates revealed its critical role in phytohormone metabolism. Ectopic overexpression of PmFLC-like in Arabidopsis delayed flowering and reduced plant size. Consistently, PmFLC-like expression was significantly higher in the flower buds of a late-blooming P. mume cultivar than in an early-blooming one. Furthermore, PmFLC-like overexpression led to increased abscisic acid (ABA) and decreased cytokinin (CTK) accumulation, aligning with our observation that PmFLC-like expression correlated positively with ABA levels and negatively with CTK levels in P. mume flower buds. Transcriptome analysis suggested that PmFLC-like expression was associated with ABA- and cytokinin-related co-expression modules, including ABA catabolism-related genes such as CYP707A and UDP-glycosyltransferases, and Cytokinin dehydrogenase ( CKX ). Exogenous ABA and fluridone treatments up- and downregulated PmFLC-like expression, respectively, indicating an ABA- PmFLC-like positive feedforward loop during flower bud development. Collectively, these results suggest that PmFLC-like is associated with ABA/CTK metabolism and winter flower bud development in P. mume. Co-expression with genes involved in ncRNA metabolism and histone modification further suggests a possible link with chromatin-related regulatory processes.