Abstract
Bud dormancy is a critical adaptive trait in woody plants, essential for enduring harsh winter conditions. The relationship between bud break timing and cold resistance is complex and has been a subject of debate. This study utilizes a Genome-Wide Association Study (GWAS) on 201 natural mulberry populations to identify the MaFAD2 gene, which shows the strongest association with bud break timing. Known for its role in cold resistance, MaFAD2's link to bud break timing suggests a direct correlation between these traits. Expression analysis of MaFAD2 in mulberry trees indicates peak activity in dormant buds, declining as dormancy ends. Selective sweep analysis on germplasms from contrasting climates reveals positive selection in MaFAD2 in cold-resistant Uzbek germplasms. Overexpression of MaFAD2 in early-budding germplasms significantly delays bud break, confirming its regulatory role. These findings highlight MaFAD2 as a key determinant of cold tolerance variability among mulberry germplasms, with its expression directly correlated with bud break timing. This provides a molecular basis for selecting cold-resistant mulberry germplasms based on bud break timing in breeding programs.