Antisense acid invertase (TIV1) gene alters soluble sugar composition and size in transgenic tomato fruit

Invertase (beta-fructosidase, EC 3.2.1.26) hydrolyzes sucrose to hexose sugars and thus plays a fundamental role in the energy requirements for plant growth and maintenance. Transgenic plants with altered extracellular acid invertase have highly disturbed growth habits. We investigated the role of intracellular soluble acid invertase in plant and fruit development. Transgenic tomato (Lycopersicon esculentum Mill.) plants expressing a constitutive antisense invertase transgene grew identically to wild-type plants. Several lines of transgenic fruit expressing a constitutive antisense invertase gene had increased sucrose and decreased hexose sugar concentrations. Each transgenic line with fruit that had increased sucrose concentrations also had greatly reduced levels of acid invertase in ripe fruit. Sucrose-accumulating fruit were approximately 30% smaller than control fruit, and this differential growth correlated with high rates of sugar accumulation during the last stage of development. These data suggest that soluble acid invertase controls sugar composition in tomato fruit and that this change in composition contributes to alterations in fruit size. In addition, sucrose-accumulating fruit have elevated rates of ethylene evolution relative to control fruit, perhaps as a result of the smaller fruit size of the sucrose-accumulating transgenic lines.