Antisense RNA inhibition of pyruvate, orthophosphate dikinase and NADP malate dehydrogenase in the C₄ 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 C₄ dicot Flaveria bidentis L. var. Kuntze produced several independent transgenic lines with leaves showing heritable, mosaic phenotypes. The appearance of these plants was highly variable, with leaves that were either predominantly green, predominantly yellow, or a mixture of the two. The yellow sectors 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 respective target enzyme compared to wild-type leaves. The mRNA of the target enzyme was reduced in both green and yellow sectors o f leaves of both types of transformants compared to leaves from wild-type plants. The yellow sectors 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 attributed 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 effectiveness of the antisense transgenes for the analysis of transgenic plants in general is discussed.