Expression of C4 Genes in Development of Maize Leaf Cell Types

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The development of a complex organ such as a leaf depends on the integrated differentiation of multiple cell types. The alterations in gene expression which contribute to the differentiation of the two interacting photosynthetic cell types in maize leaves (bundle sheath and mesophyll) are most dramatic among the genes for enzymes which interact in C4 carbon fixation. Each C4 enzyme is specific to one cell type, and accumulates in a fixed spatial pattern within the leaf. The means by which expression of each photosynthetic C4 gene occurs specifically in one of the two leaf cell types during development are unknown. Several of the C4 enzymes are members of small multigene families which also contribute enzyme isoforms which perform housekeeping functions and are regulated in drastically differing manner from the photosynthetic forms. This project seeks to extend previous studies of C4 enzyme genes and patterns of cellular development in leaves by directly comparing genes for the photosynthetic and non- photosynthetic isoforms. The gene cloning, sequencing and comparative studies will also provide gene-specific probes to aid in subsequent analysis of cell-specific and organ-specific gene expression.