TRICHO-TOR: TOR kinase signaling in the mycoparasite Trichoderma atroviride

Species of the fungal genus Trichoderma are among the most commonly isolated moulds from various habitats world-wide. These fungi display a remarkable variety of lifestyles amongst which mycoparasitism today is known to be the innate nature of the whole genus. Mycoparasites are able to parasitize and prey on other fungi, a property that renders them interesting and sustainable alternatives to synthetic fungicides. The antagonistic success of Trichoderma mycoparasites is largely dependent on the fungus ability to quickly and adequately react to environmental cues and to produce bio-molecules such as lytic enzymes and secondary metabolites for competing and attacking other fungi. A pre-requisite for successful mycoparasitism is the sensing of respective prey fungi which includes pre-contact prey recognition and re-programming of cellular activities in Trichoderma. We could show previously that conserved signal transduction pathways govern the activation of the mycoparasitic response in Trichoderma atroviride. In addition, we know that sensing of the prey results in stress response reactions in the mycoparasite, which resemble those triggered by nitrogen limitation and which include key components known to be involved in nitrogen sensing in other organisms. In this project entitled Tricho-TOR: TOR kinase signalling in the mycoparasite Trichoderma atroviride, we plan to unravel in T. atroviride the function of key components of the TOR signalling pathway, the central nitrogen sensing pathway in eukaryotes. We want to identify how signalling via the TOR kinase and its up- and down-stream components cooperates with known mycoparasitism- relevant signal transduction cascades in order to regulate respective cellular outputs. These key aspects of the project will be tackled by generating respective T. atroviride mutants genetically interrupted in central hubs of the TOR pathway and analyzing their basic biological and mycoparasitism-specific phenotypes. In addition, novel regulators of TOR signalling shall be screened for by using protein- protein interaction-based methods in order to identify upstream components involved in sensing. By including a collection of available signalling mutants with alterations in their mycoparasitic activities, functional interrelations with the TOR pathway will be identified. The expected outcomes will significantly contribute to our understanding of the interrelation between nutrient sensing and the mechanisms governing the recognition of prey fungi and the triggering of the mycoparasitic response. As the production of several enzymes and secondary metabolites of industrial interest is quantitatively as well as qualitatively regulated by nitrogen availability, the genetic manipulation of the TOR signalling pathway may result in interesting applications as well.

Mycoparasitic fungi antagonize other fungi by overgrowing and parasitizing their fungal preys. Trichoderma atroviride is a potent mycoparasite applied as sustainable alternative to synthetic fungicides in the protection of plants against fungal phytopathogens. Its mycoparasitic activity involves processes shared with plant and human pathogenic fungi such as the production of cell wall degrading enzymes and secondary metabolites and is tightly regulated by environmental cues including nutrients and prey fungus-derived signals. We uncovered the TOR (Target Of Rapamycin) kinase pathway, which is known from studies in yeast and mammalian cells to regulate growth in response to nutrient availability, as an essential signalling hub in Trichoderma atroviride. Trichoderma atroviride possesses a single TOR kinase, which we named Tor1. Alteration of Tor1 activity by treatment with chemical inhibitors or by genetic manipulation of selected TOR pathway components revealed Tor1 signaling as a key player in regulating growth and metabolism as well as mycoparasitism-relevant functions. Our results provide the first in-depth insights into the role of this important regulatory pathway in a mycoparasitic fungus which is of utmost importance for the enhancement and targeted application of Trichoderma atroviride as a biocontrol agent.