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Fruit of tomato (Solanum lycopersicum), like those from many species, have been characterized to undergo a shift from partially photosynthetic to truly eterotrophic metabolism. While there is plentiful evidence for functional photosynthesis in young tomato fruit, the rates of carbon assimilation rarely exceed those of carbon dioxide release, raising the question of its role in this tissue. Here, we describe the generation and characterization of lines exhibiting a fruit-specific reduction in the expression of glutamate 1-semialdehyde aminotransferase (GSA). Despite the fact that these plants contained less GSA protein and lowered chlorophyll levels and photosynthetic activity, they were characterized by few other differences. Indeed, they displayed almost no differences in fruit size, weight, or ripening capacity and furthermore displayed few alterations in other primary or intermediary metabolites. Although GSA antisense lines were characterized by significant alterations in the expression of genes associated with photosynthesis, as well as with cell wall and amino acid metabolism, these changes were not manifested at the phenotypic level. One striking feature of the antisense plants was their seed phenotype: the transformants displayed a reduced seed set and altered morphology and metabolism at early stages of fruit development, although these differences did not affect the final seed number or fecundity. Taken together, these results suggest that fruit photosynthesis is, at least under ambient conditions, not necessary for fruit energy metabolism or development but is essential for properly timed seed development and therefore may confer an advantage under conditions of stress.
Fruit development is a tightly genetically controlled process, unique to flowering plants, which provides both a suitable environment for seed maturation and a mechanism for their dispersal. Given the fundamental nature of both the dietary and biological significance of fruit, the molecular dissection of fruit development has recently received considerable interest (Manning et al., 2006; Vrebalov et al., 2009;Wang et al., 2009). The fruit is the result of the development of the ovary, with fruit organogenesis originating from a flower primordium, with the mature flower either being fertilized (and developing into a fruit) or not (and entering the abscission process; Vivian-Smith and Koltunow, 1999; Wang et al., 2009). Considerable advances have recently been made in understanding key elements of the genetic control of ripening and development (Giovannoni, 2007; Seymour et...