Expression profiles of tissues- or organs-specific ClaSWEET genes in one cultivated and two wild varieties of watermelon. (a) The expression profiles of cultivated variety Sugar baby. (b) The expression profiles of wild variety PI296341-FR. (c) The expression profiles of wild variety YL. The total RNA was extracted from R (roots), S (stems), L (leaves), T (tendrils), F (female flowers), and M (male flowers) of three varieties of watermelon. Red and green correspond to strong and weak expression of the ClaSWEET genes, respectively. The phylogenetic tree was built with average linkage clustering method.