RrLHY regulates arginine biosynthesis by activating RrNAGS1 in Rosa roxburghii fruit

Rosa roxburghii Tratt., a member of the Rosaceae family, is a plant of considerable medicinal and economic value. Its fruit is notably rich in arginine. Integrated genomic and transcriptomic analyses of R. roxburghii fruit identified 21 genes implicated in arginine synthesis and 4 genes involved in arginine catabolism. Among these, N-acetylglutamate synthase (RrNAGS1) and arginine decarboxylase (RrADC1) were found to be strongly correlated with arginine accumulation in the fruit. Functional validation through overexpression demonstrated that RrNAGS1 promotes arginine accumulation, increasing by 15% in hydrolyzed and 100% in free arginine, respectively. In contrast, RrADC1 suppresses this process, with corresponding decreases of 17% and 34%. Furthermore, we identified the nucleus-localized transcription factor RrLHY (LATE ELONGATED HYPOCOTYL) that binds to and activates the promoter of RrNAGS1. Overexpression of RrLHY upregulated RrNAGS1 and consequently increased hydrolyzed and free arginine levels by 67% and 111%, respectively, establishing its central role in regulating arginine biosynthesis. Our findings elucidate the biosynthetic mechanism of arginine in R. roxburghii fruit, provide insights into arginine metabolism in other crops, and aid the development of medicinal and edible products.