Red and far-red light improve the antagonistic ability of Trichoderma guizhouense against phytopathogenic fungi by promoting phytochrome-dependent aerial hyphal growth.

Light as a source of information regulates morphological and physiological processes of fungi, including development, primary and secondary metabolism, or the circadian rhythm. Light signaling in fungi depends on photoreceptors and downstream components that amplify the signal to govern the expression of an array of genes. Here, we investigated the effects of red and far-red light in the mycoparasite Trichoderma guizhouense on its mycoparasitic potential. We show that the invasion strategy of T. guizhouense depends on the attacked species and that red and far-red light increased aerial hyphal growth and led to faster overgrowth or invasion of the colonies. Molecular experiments and transcriptome analyses revealed that red and far-red light are sensed by phytochrome FPH1 and further transmitted by the downstream MAPK HOG pathway and the bZIP transcription factor ATF1. Overexpression of the red- and far-red light-induced fluffy gene fluG in the dark resulted in abundant aerial hyphae formation and thereby improvement of its antagonistic ability against phytopathogenic fungi. Hence, light-induced fluG expression is important for the mycoparasitic interaction. The increased aggressiveness of fluG-overexpressing strains was phenocopied by four random mutants obtained after UV mutagenesis. Therefore, aerial hyphae formation appears to be a trait for the antagonistic potential of T. guizhouense. Author summary: Light controls a large proportion of the genome. While Trichoderma species encode the red-light receptor phytochrome, a detailed study of red-light responses and signaling was lacking. Here, we show that the mycoparasitic fungus Trichoderma guizhouense uses distinct strategies to attack phytopathogenic fungi. It can overgrow or invade the colonies of the attacked species. Red and far-red light promoted aerial hyphal growth and thereby increased both, overgrowth or invasion of the host colonies. The effect required the phytochrome-signaling pathway. We further show that screening for mutants producing more aerial hyphae proves to be an easy way to develop strains with improved biocontrol performance. [ABSTRACT FROM AUTHOR]