Trichoderma: sensing the environment for survival and dispersal.

Species belonging to the genus Trichoderma are free-living fungi common in soil and root ecosystems, and have a broad range of uses in industry and agricultural biotechnology. Some species of the genus are widely used biocontrol agents, and their success is in part due to mycoparasitism, a lifestyle in which one fungus is parasitic on another. In addition Trichoderma species have been found to elicit plant defence responses and to stimulate plant growth. In order to survive and spread, Trichoderma switches from vegetative to reproductive development, and has evolved with several sophisticated molecular mechanisms to this end. Asexual development (conidiation) is induced by light and mechanical injury, although the effects of these inducers are influenced by environmental conditions, such as nutrient status and pH. A current appreciation of the links between the molecular participants is presented in this review. The photoreceptor complex BLR-1/BLR-2, ENVOY, VELVET, and NADPH oxidases have been suggested as key participants in this process. In concert with these elements, conserved signalling pathways, such as those involving heterotrimeric G proteins, mitogen-activated protein kinases (MAPKs) and cAMP-dependent protein kinase A (cAMP-PKA) are involved in this molecular orchestration. Finally, recent comparative and functional genomics analyses allow a comparison of the machinery involved in conidiophore development in model systems with that present in Trichoderma and a model to be proposed for the key factors involved in the development of these structures.