Molecular mapping of the cnx2 locus involved in molybdenum cofactor biosynthesis in rice (Oryza sativa L.)

Molybdenum cofactor (Moco) is essential for nitrate reductase (NR), xanthin e dehydrogenase (XDH), and aldehyde oxidase to perform their catalytic func tions in plants. Moco biosynthesis is a complex process involving many gene s. Little is known about the genetics and molecular aspects of Moco biosynt hesis in plants and other eukaryotes. In rice, we previously isolated a Moc o mutant C25 with a mutation in the CNX2 gene from a mutagenized indica cul tivar IR30 and characterized its biochemical properties. This mutant was cr ossed with a japonica cultivar, Norin 8, to investigate the linkage of cnx2 to restriction fragment length polymorphism (RFLP) and cleaved amplified p olymorphic sequence (CAPS) markers. Chlorate resistance was used to trace t he cnx2 mutation because of its cosegregation with the loss of NR and XDH a ctivities observed earlier. RFLP and CAPS analyses show the location of the cnx2 locus on the long arm of chromosome 4. It is mapped between RFLP mark ers C513 and C377 with a distance of 9.5 and 13.1 cM, respectively. It is a lso linked with CAPS marker RA0738 at a distance of 30.3 cM.