The Mitochondrial Folylpolyglutamate Synthetase Gene Is Required for Nitrogen Utilization during Early Seedling Development in Arabidopsis

Investigations into the biochemical processes and regulatory mechanisms of nitrogen (N) utilization can aid in understanding how N is used efficiently in plants. This report describes a deficiency in N utilization in an Arabidopsis ( Arabidopsis thaliana ) transfer DNA insertion mutant of the mitochondrial folylpolyglutamate synthetase gene DFC , which catalyzes the conjugation of glutamate residues to the tetrahydrofolate during folate synthesis. The mutant seedlings displayed several metabolic changes that are typical of plant responses to low-N stress, including increased levels of starch and anthocyanin synthesis as well as decreased levels of soluble protein and free amino acid, as compared with those in wild-type seedlings when external N was sufficient. More striking changes were observed when dfc seedlings were grown under N-limited conditions, including shorter primary roots, fewer lateral roots, higher levels of glycine and carbon-N ratios, and lower N content than those in wild-type seedlings. Gene expression studies in mutant seedlings revealed altered transcript levels of several genes involved in folate biosynthesis and N metabolism. The biochemical and metabolic changes also suggested that N assimilation is drastically perturbed due to a loss of DFC function. The observation that elevated CO 2 partly rescued the dfc phenotypes suggests that the alterations in N metabolism in dfc may be mainly due to a defect in photorespiration. These results indicate that DFC is required for N utilization in Arabidopsis and provide new insight into a potential interaction between folate and N metabolism.