Differential expression of the gene for the large subunit of ribulose bisphosphate carboxylase in maize leaf cell types.

Mesophyll cells and bundle sheath cells, the dimorphic photosynthetic cell types in the C4 plant Zea mays, differ in protein composition. In particular, the large subunit of the chloroplast enzyme ribulose-1,5-bisphosphate carbocylase (EC 4.1.1.39) is found entirely or almost exclusively in bundle sheath cells. The DNA sequence coding for this polypeptide is contained in the chloroplast DNA of both mesophyll cells and bundle sheath cells. RNA complementary to this coding sequence has been detected in RNA from bundle sheath cells, but is almost or entirely absent from mesophyll cells. Similarly, translatable mRNA for this polypeptide has been detected in RNA from bundle sheath cells, but not from mesophyll cells. Portions of the 4200 base pair maize plastid DNA sequence Bam 9 outside the large subunit gene region appear to be transcribed in mesophyll cells. Thus differential gene expression at the mRNA level has been directly demonstrated to occur in these two cell types.