Genomic and cDNA clones for maize phosphoenolpyruvate carboxylase and pyruvate,orthophosphate dikinase: Expression of different gene-family members in leaves and roots.

We have isolated cDNA clones for the maize leaf enzymes phosphoenolpyruvate (P-ePrv) carboxylase [orthophosphate:oxaloacetate carboxy-lyase (phosphorylating) EC 4.1.1.31] and pyruvate,orthophosphate (Prv,P(i)) dikinase (ATP:pyruvate,orthophosphate phosphotransferase, EC 2.7.9.1) by exploiting the light-inducibility and large size of the mRNAs (3.5 kilobases) that encode the two enzymes. The clones were identified by hybrid-selection and immunoprecipitation assays. From a maize genomic library, two different types of genomic clones were screened with both the P-ePrv carboxylase and the Prv,P(i) dikinase cDNA clones. Information from these genomic clones and genome blots indicates that the P-ePrv carboxylase gene family has at least three members and the Prv,P(i) dikinase family at least two. Transcripts for both enzymes were detected in green leaves, etiolated leaves, and roots. The results show that the P-ePrv carboxylase mRNAs in green leaves and roots are encoded by different genes. Whereas the P-ePrv carboxylase mRNAs in all three tissues appear to be the same size, the Prv,P(i) dikinase mRNA in green leaves is about 0.5 kilobases longer than the Prv,P(i) dikinase mRNAs in etiolated leaves and roots. It is possible that all these Prv,P(i) dikinase transcripts are encoded by one gene, and the size differences may correspond to the presence or absence of a sequence encoding a chloroplast transit peptide.