Catalase-1 (CAT-1) and nucleoside diphosphate kinase-1 (NDK-1) play an important role in protecting conidial viability under light stress in Neurospora crassa.

Recently we reported that Catalase-1 (CAT-1) played an important role in protecting conidial viability in Neurospora crassa, and interacted with a light signal transducer, nucleoside diphosphate kinase-1 (NDK-1). To disclose the functional interaction between CAT-1 and NDK-1 at the genetic level, we created CAT-1 and NDK-1 double mutants, cat-1;ndk-1-1 and cat-1;ndk-1-2, by crossing single mutants of cat-1 ( RIP ) and ndk-1 ( P72H ) previously isolated in our laboratory. The double mutant strains grew normally, but showed increased CAT-2 activity. In cat-1 ( RIP ), NDK activity was increased when dCDP was used as a substrate. ndk-1 ( P72H ), cat-1;ndk-1-1, and cat-1;ndk-1-2 were more sensitive to riboflavin than the wild type and cat-1 ( RIP ) under strong light (100 microE m(-2) s(-1)). The pull-down experiment suggests that His-tagged NDK-1 is bound to [(32)P]NADH. However, his-tagged NDK-1(P72H) was not bound to [(32)P]NADH. The double mutants showed much lower conidial viability and lost all conidial germination ability much more rapidly than cat-1 ( RIP ), when they were cultured under continuous light for more than 2 weeks. These results indicate that the interaction of CAT-1 with NDK-1 plays an important role in supporting the survival of conidia under oxidative and light-induced stress including singlet oxygen, and confirm our former conclusion that reactive oxygen species play an important role in light signal transduction via NDK-1 at the genetic level.