Exogenous Melatonin Promotes Cold Tolerance in Grape Seedlings: Physiological, Transcriptomic, and Functional Evidence

Melatonin (MEL) is an antioxidant
molecule that enhances
plant
tolerance to environmental stress. However, the mechanisms by which
MEL regulates cold signaling pathways in grapes under cold stress
remain elusive. Here, we investigated the physiological and transcriptomic
changes in grape seedlings treated with exogenous MEL to determine
their protective role under cold stress. Results showed that 150 μM
MEL effectively attenuated cold-induced cell damage by reducing reactive
oxygen species (ROS) and preserving the chloroplast structure and
function. MEL also inhibited tannin degradation, which contributed
to its protective effect. Exogenous MEL promoted the synthesis of
endogenous MEL, abscisic acid, auxin, and cytokinin while inhibiting
gibberellin. Transcriptomic profiling revealed 776 differentially
expressed transcripts in MEL-treated samples compared to controls.
Functional analysis of a candidate hub gene, VvHSFA6b, showed that its overexpression in grape calli enhances cold tolerance
by activating jasmonic acid synthesis pathway genes, promoting JA
accumulation, and inhibiting JAZ-repressed transcription factors.