Genome-Wide Analysis of the R2R3-MYB Gene Family in Durian (Durio zibethinus) and Potential Role in Nutrient Stress Response

The R2R3-MYB gene family is among the most expansive families of transcription factors. A growing amount of evidence indicates that members of this family control the transcription of structural genes associated with plant growth and development and respond to various stresses, including nutrient stress. Durian, an iconic fruit in Southeast Asia, is highly susceptible to nutrient stress, which can greatly impact its production and quality. However, the specific effects of nutrient stress on phytochemicals, sugars, fatty acids, sensory attributes and gene expression remain unknown. This study investigates the effects of nutrient stress on phytochemical content and explores the underlying molecular mechanisms, with a particular focus on the expression of R2R3-MYB genes. Nutrient-stressed durian fruits showed significantly reduced levels of total phenolics, anthocyanins, flavonoids, ascorbic acid, lipids, and sugars compared to those grown under NPK-fertilised conditions. Sensory analyses further revealed a significant decline in sweetness, bitterness, creaminess, smoothness, and stickiness in fruits subjected to nutrient stress. To elucidate the molecular response, 218 R2R3-MYB genes were identified and classified into six subgroups based on phylogenetic analysis, with 69.7% containing three exons and two introns, all predicted to localise in the nucleus. Amino acid analysis revealed 10 distinct motifs. Further expression analysis of 22 nutrient stress-associated DzMYB genes showed significant upregulation of 20 genes in the leaves under nutrient-stressed conditions. This study provides valuable insights into the effects of nutrient stress on durians and establishes a foundation for future field-based research while identifying key R2R3-MYB genes that regulate nutrient stress responses.