Characterization of watermelon fruitlet development

Watermelon (Citrullus lanatus var. lanatus) fruit produce low amounts of ethylene during ripening and is therefore considered as a non-climacteric fruit. Here we examined the involvement of ethylene in early stages of fruit development. Ethylene production was high in ovary and young fruitlets but decreased at later stages of development. Increased fruit set was observed in plants treated with ethylene biosynthesis inhibitor. To identify genes involved in the process we isolated genes encoding for the rate-limiting enzyme in ethylene biosynthesis pathway, 1-aminocyclopropane-1-carcoxylate synthase (ACC synthase, ACS). The expression pattern during early fruit development of watermelon ACS genes (CitACS) was analyzed. High CitACS1 transcript level was detected in the early stages of fruit set but it decreased at later stages of fruit development. CitACS1 transcript accumulation was in direct correlation with ethylene evolution at the corresponding stages.