The DapA gene encoding the lysine biosynthetic enzyme dihydrodipicolinate synthase from Coix lacryma-jobi: cloning, characterization, and expression analysis

Dihydrodipicolinate synthase (DHPS) is the main enzyme of a specific branch of the aspartate pathway leading to lysine biosynthesis in higher plants. We have cloned and characterized the DHPS-encoding DapA gene from the maize -related grass Coix lacryma-jobi. The DapA open reading frame is interrupte d by two introns and encodes the 326 amino acid-long Coix DHPS protein, whi ch is 95% identical to the maize DHPS protein. Coix DNA gel blot analysis w ith maize DHPS cDNA as a probe showed a single strongly hybridizing band al ong with faint bands. RNA gel blot analysis showed that DHPS transcripts ar e present in coleoptiles, embryos, endosperms, and roots but are almost und etectable in blades of young leaves of both Coix and maize. The 5'-flanking region of the DapA gene contains a TGACTC GCN4-like element located 372 bp upstream the putative translation start codon. Steady-state levels of DHPS mRNA were slightly reduced in the endosperms and embryos of the maize lysi ne-rich opaque2 mutants when compared with those in normal kernels. Selecti ve binding assay with the maize Opaque2 protein (O2) showed that the GCN4-l ike element is not an O2 binding site, suggesting that the DHPS gene is not under the control of O2.