Expression of Acid Invertase Gene Controls Sugar Composition in Tomato (Lycopersicon) Fruit

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Abstract
A wild tomato species, Lycopersicon chmielewskii, accumulates high levels of soluble sugar in mature fruit and, unlike the domesticated tomato species, Lycopersicon esculentum, accumulates sucrose rather than glucose and fructose. Genetic and biochemical analyses of progeny resulting from a cross of L. chmielewskii with L. esculentum have previously indicated that the trait of sucrose accumulation is controlled by a single recessive gene and is associated with low levels of acid invertase protein in the developing fruit. Analysis of progeny from the BC2F3 generation from the L. esculentum x L. chmielewskii cross revealed that sucrose-accumulating fruit accumulate sugar in two phases corresponding to fruit expansion and fruit maturation and that the majority of the sucrose was stored in the latter phase after the fruit had reached maximum size. The only significant enzymic difference between the sucrose-accumulating and hexose-accumulating fruit was the lack of acid invertase activity in sucrose-accumulating fruit. Sucrose phosphate synthase activity did not increase in the sucrose-accumulating fruit during late development when the rate of sucrose accumulation increased. The lack of acid invertase activity in sucrose-accumulating fruit was correlated with inheritance of the L. chmielewskii acid invertase gene and the absence of acid invertase mRNA in developing fruit. This suggests that the L.chmielewskii invertase gene is transcriptionally silent in fruit and that this is the basis for sucrose accumulation in progeny derived from the interspecific cross of L. esculentum and L. chmielewskii.