Expression of the C-4 Me1 gene from Flaveria bidentis requires an interaction between 5' and 3' sequences

The efficient functioning of C-4 photosynthesis requires the strict compartmentation of a suite of enzymes in either mesophyll or bundle sheath cells. To determine the mechanism controlling bundle sheath cell-specific expression of the NADP-malic enzyme, we made a set of chimeric constructs using the 5' and 3' regions of the Flaveria bidentis Me1 gene fused to the beta-glucuronidase gusA reporter gene. The pattern of GUS activity in stably transformed F. bidentis plants was analyzed by histochemical and cell separation techniques. We conclude that the 5' region of Me1 determines bundle sheath specificity, whereas the 3' region contains an apparent enhancer-like element that confers high-level expression in leaves. The interaction of 5' and 3' sequences was dependent on factors that ape present in the C-4 plant but not found in tobacco.