ARS | Publication request: THE MAIZE VIVIPAROUS10/VIVIPAROUS13 LOCUS ENCODES THE CNX1 GENE REQUIRED FOR MOLYBDENUM COFACTOR BIOSYNTHESIS

Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 20, 2005
Publication Date: January 1, 2006
Citation: Porch, T.G., Tseung, C., Schmelz, E.A., Settles, M. 2006. The maize Viviparous 10/Viviparous 13 locus encodes the Cnx1 gene required for molybdenum cofactor biosynthesis. The Plant Journal. 45(2):250-263.

Interpretive Summary: Plants respond to changes in environmental conditions through hormones and direct sensing of chemicals that are important for plant growth. Abscisic acid (ABA), auxin, and nitrate are important signaling molecules in plants. One of the molecules necessary for their synthesis and metabolism is the molybdenum cofactor (Moco). Transposable elements are mobile DNA fragments that are able to relocate to different positions within the genome. The maize Mutator transposable element is a highly active transposable element, which when coupled with preferential insertion into genes, results in high mutation rates. Using the Mutator transposon mutagenesis system, we have identified a mutant in the viviparous13 (vp13) maize gene that lacks ABA, auxin, and nitrate signaling. We devised a novel PCR-based method to identify the vp13 gene using the mutator transposon that caused the mutation. The vp13 mutants were found to be defective in Moco synthesis and disrupted in the ABA, auxin, and nitrate signaling processes. Vp13 was found to encode the equivalent of the plant Cnx1 protein or the mammalian gephyrin. Gephyrin catalyzes the final common step of Moco synthesis and is a scaffolding protein. Considering these observations in vp13 and similar mutations in Arabidopsis, we propose that the Moco biosynthetic pathway regulates the metabolism of auxin, ABA, and nitrate to influence plant environmental responses. These finding add to the understanding of the response of plants to the environment and can be used in the effort to improve crop tolerance to abiotic stress, a major limitation to crop production worldwide.

Technical Abstract: Abscisic acid (ABA), auxin, and nitrate are important signaling molecules that affect plant-environment growth responses. The synthesis and metabolism of these compounds depends upon the molybdenum cofactor (Moco). Maize viviparous13 (vp13) mutants have characteristic seedling lethal phenotypes consistent with disruptions in ABA, auxin, and nitrate signaling. We devised a novel PCR-based method to clone a transposon tagged allele of vp13. Vp13 encodes the ortholog of plant Cnx1 or mammalian gephyrin. Gephyrin catalyzes the final common step of Moco synthesis and is a scaffolding protein. ABA and auxin levels are reduced in vp13 mutants, and vp13 seedlings lack Moco-dependent enzyme activities. A weak allele of Arabidopsis cnx1 does not disrupt ABA signaling and has an analogous phenotype to sir1, a likely Moco biosynthetic mutation that disrupts auxin signaling. Considering these observations, we propose that the Moco biosynthetic pathway regulates the metabolism of auxin, ABA, and nitrate to influence plant environmental responses.