l-Arginine is essential for conidiation in the filamentous fungus Coniothyrium minitans

Conidiation is important in the life cycles of mitosporic fungi for survival and transmission. A full-length cDNA of one gene named CMCPS1 encoding l-arginine-specific carbamoyl-phosphate synthase was obtained from Coniothyrium minitans, a sclerotial parasite of the plant pathogenic fungus Sclerotinia sclerotiorum. T-DNA insertional disruption of CMCPS1 resulted in conidiation deficiency of mutant ZS-1T2029, and this was confirmed with the RNAi technique. The phenotype was restored by complementation with l-arginine, and the effect of l-arginine on conidiation may be mediated by nitric oxide, which is catalyzed by nitric oxide synthase (NOS). Conidiation of ZS-1T2029 was restored by sodium nitroprussiate, a NO donor; and conidiation of wild type strain ZS-1 could be suppressed by l-NAME, an inhibitor of NOS. The highest amount of NO in mycelia was detected at an early stage of conidiation (72 hpi) in liquid shake culture medium. Staining with the NO-sensitive fluorescent probe, DAF-FM DA, gave strong fluorescent signals in primordia and young pycnidia. This work presents the first report that l-arginine is involved in conidiation of C. minitans, and the possibility of l-arginine-derived nitric oxide-mediated conidiation among fungi and possible modes of action are discussed.