DOWN-REGULATION OF 2 NONHOMOLOGOUS ENDOGENOUS TOMATO GENES WITH A SINGLE CHIMERIC SENSE GENE CONSTRUCT

Tomatoes (Lycopersicon esculentum Mill cv. Ailsa Craig) were transform ed with a gene construct having 244 bp of the 5' end of a polygalactur onase (PG) cDNA, coding for a 71 amino acid N-terminal extension to th e mature protein, fused to 1320 bp of a pectinesterase (PE) cDNA encod ing the full sequence of the mature PE protein. This chimaeric gene wa s inserted in a sense orientation between a CaMV 35S promoter and term inator for constitutive expression. In transformed tomato plants expre ssion of the endogenous PG and PE genes in the fruit was inhibited; th ere was little or no observable PG and PE mRNA and a substantial reduc tion in the level of PG and PE enzyme activity. The transgene was expr essed in the leaves of the transformed plants as demonstrated by the a ccumulation of mRNA, but no protein product could be identified. Howev er, no transgene mRNA or protein were observed in the transgenic fruit . This paper represents the first report of the down-regulation of two non-homologous endogenous genes using a single gene construct. A sens e gene construct was responsible for these effects. These findings are discussed in relation to possible mechanisms of action of co-suppress ion.