Genome-Wide Identification of UGT Genes and Analysis of Their Expression Profiles During Fruit Development in Walnut (Juglans regia L.)

Abstract

Walnut (Juglans regia L.) possesses the ability to prevent coronary heart disease and promote cardiovascular health. This ability can be attributed to their rich content of polyphenols, particularly flavonoids. The biosynthesis of flavonoids is reliant on the catalytic activity of uridine diphosphate glycosyltransferase (UGT). However, the identification of UGTs in walnut has not been reported. In the current study, a total of 124 UGT genes containing the PSPG box were identified from the walnut genome. Based on phylogenetic analysis, the 124 UGTs could be classified into 16 distinct groups, which exhibited an uneven distribution across the 16 chromosomes. Subcellular localization prediction analysis revealed that approximately 78.23% of walnut UGT proteins were predominantly localized in the cytoplasmic compartment. Furthermore, motif annotation confirmed that motifs 1, 2, and 3 represented conserved structural features within UGT proteins, while interestingly, around 56.5% of walnut UGT members lacked introns. Through the analysis of promoter cis-regulatory elements, it was revealed that JrUGTs are involved in photoresponse, hormonal regulation, and other physiological responses. In conjunction with transcriptome analysis and quantitative expression, approximately 39% of UGT genes in walnut exhibited high expression levels during early fruit development. Correlation analysis between UGT genes’ expression and phenolic content in walnut indicated that JrUGT6, JrUGT38, JrUGT39, JrUGT58, JrUGT69, JrUGT75, and JrUGT82 might be involved in phenolic biosynthesis in walnut. This comprehensive study provides an overview of the UGT genes in walnut, serving as a valuable reference and theoretical foundation for further investigations into the biological functions of JrUGTs in flavonoid biosynthesis.