LEAF PERMEASE1 GENE OF MAIZE IS REQUIRED FOR CHLOROPLAST DEVELOPMENT

Adjacent bundle sheath and mesophyll cells cooperate for carbon fixati on in the leaves of C4 plants. Mutants with compromised plastid develo pment should reveal the degree to which this cooperation is obligatory , because one can assay whether mesophyll cells with defective bundle sheath neighbors retain C4 characteristics or revert to C3 photosynthe sis. The leaf permease1-mutable1 (Ipe1-m1) mutant of maize exhibits di srupted chloroplast ultrastructure, preferentially affecting bundle sh eath choroplasts under lower light. Despite the disrupted ultrastructu re, the metabolic cooperation of bundle sheath and mesophyll cells for C4 photosynthesis remains intact. To investigate this novel mutation, the Activator transposon-tagged allele and cDNAs corresponding to the Lpe1 mRNA from wild-type plants were cloned. The Lpe1 gene encodes a polypeptide with significant similarity to microbial pyrimidine and pu rine transport proteins. An analysis of revertant sectors generated by Activator excision suggests that the Lpe1 gene product is cell autono mous and can be absent up to the last cell divisions in the leaf primo rdium without blocking bundle sheath chloroplast development.