The cab-m7 gene: a light-inducible, mesophyll-specific gene of maize.

Southern blot analysis has revealed the existence in maize of perhaps 12 members of the nuclear cab multigene family encoding the chlorophyll a- and b-binding proteins of the photosystem II light-harvesting complex. Hybridization with 3' probes derived from unsequenced cDNA clones showed that six members of this family differ from one another with respect to expression in mesophyll and/or bundle sheath cells and regulation by light. An additional member of this family, designated cab-m7, that encodes a 28 kDa primary translation product has now been identified. It has been cloned from a maize genomic library and sequenced to begin to define the bases for differences in the expression of these genes. This cab gene is shown to be strongly preferentially expressed in the mesophyll (vs. bundle sheath) cells of maize. Furthermore, the gene is photo-responsive; although small amounts of cab-m7 mRNA are present in etiolated leaves, the mRNA pool is 8-fold larger after six hours of illumination. DNA sequences upstream of the cab-m7 gene resemble those found in the 5'-flanking regions of some other plant genes.