Molecular characterization of dihydroneopterin aldolase and aminodeoxychorismate synthase in common bean-genes coding for enzymes in the folate synthesis pathway.

Common beans (Phaseolus vulgaris) are excellent sources of dietary folates, but different varieties contain different amounts of these compounds. Genes coding for dihydroneopterin aldolase (DHNA) and aminodeoxychorismate synthase (ADCS) of the folate synthesis pathway were characterized by PCR amplification, BAC clone sequencing, and whole genome sequencing. All DHNA and ADCS genes in the Mesoamerican cultivar OAC Rex were isolated and compared with those genes in the genome of Andean genotype G19833. Both genotypes have two functional DHNA genes and one pseudo gene. PvDHNA1 and PvDHNA2 proteins have similar secondary structures and conserved residues as DHNA homologs in Staphylococcus aureus and Arabidopsis. Sequence analysis and synteny mapping indicated that PvDHNA1 might be a duplicated and transposed copy of PvDHNA2. There is only one ADCS gene (PvADCS) identified in the bean genome and it is identical in OAC Rex and G19833. PvADCS has the conserved motifs required for catalytic activity similar to other plant ADCS homologs. DHNA and ADCS gene-specific markers were developed, mapped, and compared to their physical locations on chromosomes 1 and 7, respectively. The gene-specific markers developed in this study should be useful for detection and selection of varieties with enhanced folate contents in bean breeding programs.