CONSTITUTIVE EXPRESSION OF A FRUIT PHYTOENE SYNTHASE GENE IN TRANSGENIC TOMATOES CAUSES DWARFISM BY REDIRECTING METABOLITES FROM THE GIBBERELLIN PATHWAY

Tomato plants transformed with a copy of the fruit-expressed phytoene synthase cDNA under control of the CaMV 35S promoter showed ectopic pr oduction of carotenoids. High expressers were reduced in stature. The dwarf character was inherited with an inverse relationship between exp ression of phytoene synthase and plant height. Severely affected plant s also showed reduced chlorophyll content in young leaves. These dwarf s showed a 30-fold reduction in levels of gibberellin A(1) (GA(1)) and growth was partially restored by treatment with exogenous GA(3). Qual itative and quantitative changes in carotenoids were also found. It is proposed that the dwarf phenotype results from the over-production of phytoene synthase, which converts geranylgeranyl diphosphate to phyto ene and thereby diverts this intermediate away from the gibberellin (G A) and phytol biosynthetic pathways.