Vernalization Attenuates Age-Dependent Decline of Glucosinolates in Cabbage (Brassica oleracea ssp. capitata) through Coordinated Transcriptomic and Metabolomic Reprogramming

Vernalization, a prolonged exposure to low temperature occurs in many winter-annual, biennial, and perennial plants and is accompanied by extensive developmental and metabolic reprogramming. Glucosinolates (GSLs) are sulfur- and nitrogen-containing secondary metabolites predominantly found in the Brassicaceae family, where they play crucial roles in defense against abiotic and biotic stresses, while also conferring health benefits to humans due to their anti-carcinogenic and anti-inflammatory properties. To elucidate the impact of vernalization on GSL biosynthesis in cabbage (Brassica oleracea ssp. capitata), we performed integrated transcriptomic and metabolomic analyses in response to vernalization treatment. Metabolite profiling by HPLC revealed that total GSL content decreased progressively with plant age. However, long-term cold exposure during vernalization exerted a positive effect on total GSL accumulation, maintaining higher GSL levels compared to non-vernalized controls. RNA-seq analysis across the vernalization time course showed that more than half of the 78 identified GSL biosynthetic genes exhibited altered expression in response to vernalization. Interestingly, clustering of differentially expressed genes revealed two contrasting groups: (1) Vernalization-Repressed GSL genes (VRGs), corresponding to reduced GSL accumulation, and (2) Vernalization-Induced GSL genes (VIGs), associated with the selective induction of specific GSL compounds. Correlation analyses integrating transcriptomic and metabolite data identified key GSL pathway genes whose expression patterns were significantly correlated with profiles of aliphatic and indolic GSLs throughout vernalization. Collectively, these findings demonstrate that vernalization positively influences GSL accumulation in cabbage, with VRGs and VIGs jointly contributing to the modulation of aliphatic and indolic GSL biosynthesis under prolonged cold conditions.