Cold stress in white clover - An integrated view of metabolome and transcriptome responses

Abstract

We have studied metabolic and gene expression responses of two white clover genotypes differing in foliar basal flavonol and anthocyanin levels subjected to moderate cold in a controlled climate chamber experiment. The main flavonols and anthocyanins accumulating in white clover leaves are conjugated to galactose and xylose. Concentrations of flavonoids and sugars including starch significantly increased during cold treatment and a strong induction of flavonoid pathway genes was observed in both genotypes. Specific sugars like glucose, fructose, and starch were significantly higher in the genotype with low basal flavonoid levels. By combining metabolic and gene expression analysis we have identified two genes probably involved in the conjugation and deconjugation of flavonoids, a flavonoid galactosyltransferase and a β- galactosidase. The selected flavonoid galactosyltransferase was up-regulated by cold treatment and was also expressed at higher levels in the red leaved genotype. The β- galactosidase studied here was down-regulated by cold and expressed less in the red leaved genotype. These results indicate a tight link between primary and secondary metabolism in clover and demonstrate the value of combined metabolome and transcriptome analysis for the identification of specific gene functions.