Antisense RNA inhibition of pyruvate, orthophosphate dikinase and NADP malate dehydrogenase in the C-4 plant Flaveria bidentis: analysis of plants with a mosaic phenotype

Antisense RNA suppression of either pyruvate, orthophosphate dikinase [EC 2 .7.9.1] or NADP malate dehydrogenase [EC 1.1.1.82] gene expression in the C -4 dicot Flaveria bidentis L. var. Kuntze produced several independent tran sgenic lines with leaves showing heritable, mosaic phenotypes. The appearan ce of these plants was highly variable, with leaves that were either predom inantly green, predominantly yellow, or a mixture of the two. The yellow se ctors appeared to be clonal in origin. For both sets of transgenic plants, the green and yellow sectors showed a reduction in the activity of the resp ective target enzyme compared to wild-type leaves. The mRNA of the target e nzyme was reduced in both green and yellow sectors of leaves of both types of transformants compared to leaves from wild-type plants. The yellow secto rs had decreased amounts of other photosynthetic enzymes on an area basis, but most enzyme activities and electron transport rates were similar to the green sectors on a chlorophyll basis. The mosaic phenotype could not be at tributed simply to the degree of suppression of the target enzyme, because we have also obtained uniformly green plants with similar or greater enzyme suppression. The importance of this spatial variability in the effectivene ss of the antisense transgenes for the analysis of transgenic plants in gen eral is discussed.