Twilight,a Novel Circadian-Regulated Gene,Integrates Phototropism with Nutrient and Redox Homeostasis during Fungal Development

Phototropic regulation of circadian clock is important for environmental adaptation,organismal growth and differentiation. light plays a critical role in fungal development and virulence. however,it is unclear what governs the intracellular metabolic response to such dark-light rhythms in fungi. here,we describe a novel circadian-regulated twilight (twl) function essential for phototropic induction of asexual development and pathogenesis in the rice-blast fungus magnaporthe oryzae. the twl transcript oscillates during circadian cycles and peaks at subjective twilight. gfp-twl remains acetylated and cytosolic in the dark,whereas light-induced phosphorylation (by the carbon sensor snf1 kinase) drives it into the nucleus. the mrna level of the transcription/repair factor tfb5,was significantly down regulated in the twl∆ mutant. overexpression of tfb5 significantly suppressed the conidiation defects in the twl∆ mutant. furthermore,tfb5-gfp translocates to the nucleus during the phototropic response and under redox stress,while it failed to do so in the twl∆ mutant. thus,we provide mechanistic insight into twl-based regulation of nutrient and redox homeostasis in response to light during pathogen adaptation to the host milieu in the rice blast pathosystem. © 2015 deng et al.