UC Berkeley

Leaf and fruit size are the crucial fitness characters for plant evolution and the agronomic traits for crop yield and quality improvement in watermelon. However, the underlying genes and molecular mechanisms for regulating fruit size and biomass remain elusive. Here, we identified a Citrullus lanatus UDP-rhamnose (Rha)/UDP-galactose (Gal) transporter ClURGT4, which is localized in the Golgi apparatus and has the dual functions of transporting UDP-Gal and UDP-Rha. Loss-of-function clurgt4 mutants resulted in decreased biomass and reduced Gal, Rha, and galacturonic acid (GalA) in cell wall components. Microscopical analysis showed that ClURGT4 promoted leaf and fruit size by modulating cell expansion. Proteomic analysis revealed that several cell wall metabolism-related proteins were changed in clurgt4 mutants. Moreover, protein glycosylation was changed in the mutants, and several of the differentially glycosylated proteins were related to cell wall metabolism. These findings elucidated that ClURGT4 might control leaf and fruit size by affecting cell wall metabolism and provided a novel case for comprehensively revealing the regulatory network of watermelon biomass.