Molecular characterization of a GA-inducible gene, Cvsus1, in developing watermelon seeds.

To understand the molecular mechanisms that control seed development, we isolated a seed-preferential gene from ESTs of developing watermelon seeds. The gene Cvsusl encodes a protein that is 86% identical to the Vicia faba sucrose synthase expressed in developing seeds. RNA blot analysis showed that Cvsusl was preferentially expressed in watermelon seeds. We also investigated gene expression levels both in pollinated seeds and in parthenocarpic seeds, which lack zygotic tissues. Whereas the transcript level of Cvsusl was rapidly increased during normal seed development, the expression was not significantly increased in the parthenocarpic seeds. However, treating the parthenocarpic fruits with GA 3 strongly induced Cvsusl expression, up to the level accumulated in pollinated seeds. These results suggest that Cvsusl is induced in maternal tissues via signals from the zygotic tissues, and that GA may be one of those signals.