The partial PG gene is either inserted in the antisense orientation or in the sense orientation between the 35S promoter from cauliflower mosaic virus and the termination sequence from the nopaline synthase gene (nos) from Agrobacterium tumefaciens.  Both the antisense and sense genes down-regulate the endogenous PG gene in modified plants (Smith et al., 1988, Smith et al., 1990 a, b).  This reduces the levels of the enzyme polygalacturonase.  The enzyme is largely responsible for the breakdown of pectin in the tomato fruit. <br>Pectin is a major contributor to viscosity characteristics of processed tomato products.  Thus, the modified lines have improved consistency because of less breakdown of pectin.<br>Lines B, Da, and F have also been transformed with the nptII gene from E. coli that encodes the enzyme neomycin phosphotransferase II and serves as a selectable marker enabling identification of the transformed plant cells.  This gene is fused to the nos promoter sequence and octopine synthase termination sequence from A. tumefaciens, a known plant pest.  <br>For Line F:<br>Transgenic line F was developed from the commercial inbred line of processing tomato, TGT7, by the introduction of a truncated PG gene resulting in downregulation of the endogenous PG gene. The PG enzyme is the chief mechanism of pectin degradation in tomato fruit leading to fruit softening. The new hybrids ripen normally but experience less pectin breakdown and, therefore, have increased thickness and consistency that benefits all stages of harvesting and processing. <br>The inbred line F tomato was created by Agrobacterium-mediated transformation in which the transfer-DNA (T-DNA) contained a 3’-truncated open reading frame corresponding to the sequence of the 5’-terminal 731 nucleotides from the PG gene from the Alisa Craig variety of tomato. The expression of this truncated PG gene was controlled by inclusion of sequences from the 35S promoter of cauliflower mosaic virus and the 3’-polyadenylation signal from the nopaline synthase (nos) gene from Agrobacterium tumefaciens. In addition, the T-DNA contained sequences encoding the enzyme neomycin phosphotransferase II (NPTII) from the Tn5 transposon of Escherichia coli, strain K12, under the control of the nos promoter from A. tumefaciens. The expression of NPTII activity was used as a selectable trait to screen transformed plants for the presence of the truncated PG gene. There was no incorporation of translatable plasmid DNA sequences outside of the T-DNA region.<br>While not completely understood, the mechanism of downregulation of the endogenous PG gene is likely linked to the coordinate suppression of transcription of both the endogenous gene and the introduced truncated PG gene. Accumulation of these transcripts was reduced in red ripe fruit from the modified tomato hybrids.