Sexual development in Hypocrea jecorina

Sexual development is one of the most important achievements in evolution. Fisher and Müller stated already in 1930, that "the very existence of sex implies its advantage". Not only does it contribute to improvement of the fitness and adaptation of a given organism to its ecological niche, the fact that sexual development is induced if environmental conditions deteriorate, also indicates that this process is of utmost importance for survival of a species. The case of sexuality in the industrial workhorse Trichoderma reesei (anamorph of Hypocrea jecorina) is special in so far as both research as well as industrial strain improvement is solely based on the single isolate QM6a and its (asexual) progeny. The filamentous ascomycete T. reesei QM6a has been isolated during the world war II because it degraded army equipment made of cotton. Later on, the impressive amounts of cellulases this strain secrets, which led to its isolation in the first place, became the focus of research programs. As with all other filamentous fungi applied in industry, the possibility of crossing was not available for T. reesei, although in silico data had identified H. jecorina as its teleomorph more than a decade ago. Recently, we described the two mating type loci of T. reesei (MAT1-1 and MAT1-2) and we were for the first time able to induce sexual reproduction of T. reesei QM6a (MAT1-2) in crossings with a MAT1-1 wild-type isolate of H. jecorina, and we obtained fertilized stromata and mature ascospores . However, a serious issue with our findings was, that while male fertile, T. reesei QM6a is female sterile. In the course of the proposed project I intend to gain first insights into mechanisms related to sexual development in T. reesei. By comparison of the genomes of the female sterile strain QM6a and the fertile wild-type isolate I will select candidate genes presumable responsible for female fertility und confirm their function by deletion in the wild-type strain and complementation of QM6a. Physiological differences between strains of different mating types shall be revealed by analysis of transcription patterns and carbon source utilization patterns. Thereby intriguing insights into adjustment of the biological equilibrium between sexual and asexual development - possibly by slightly different ecological niches of mating partners - will be obtained. On the other hand, these results will contribute to selection and improvement of strains of appropriate mating type for a given application. I will further analyse the interrelationship of two genes, which impact sexual development in opposite ways in order to determine their position in the signaling cascade and their function in H. jecorina. Knowledge on sexual development in H. jecorina, as gained in the course of this project, will not only significantly increase our understanding of physiology of this fungus in nature but also boost research towards environmentally safe and economically reasonable biofuels produced from cellulosic waste material.

Trichoderma reesei (Hypocrea jecorina) is a filamentous fungus frequently used in industry for the production of diverse enzymes, especially for those able to degrade plant material. Having discovered the process of sexual crossing (sexual development) for this fungus, we realized that the most important strain of this species (QM6a) has a genetic defect and cannot form fruiting bodies without a fully fertile nature isolate as crossing partner.Hence in this project we aimed to elucidate the causes for this defect in order to be able to rescue the assumed mutations. Additionally, we wanted to understand sexual development in more detail and examined one of the molecular mechanisms related to it.One of our most interesting findings was, that Trichoderma reesei is able to sense the presence of a potential crossing partner and reacts to it by changing the secondary metabolites (chemicals acting as signals or toxins) it secretes. Accordingly, this chemical language changes if the crossing partner lacks the protein VELVET (VEL1). In such strains, not only the chemical language is perturbed, but also the production of peptide pheromones and their receptors, which receive the pheromone signal is altered. Moreover their ability for sexual development is compromised and in darkness even abolished. Consequently we found an important factor for communication between fungi and gained information on the way this communication is established.Concerning the genetic defect of QM6a we could delineate the genomic area responsible for it to 6 genes, which represents a breakthrough for industrial application. We could show that, if the wild-type version of these genes is present in the genome of QM6a, the strains had a very high probability of being fertile and the defect was alleviated. In contrast, for other genes the correlation was rather random.Transcriptome analyses further showed differences between fertile strains and QM6a. However, no crucial differences were detected between mating types (comparable to genders) in transcription of enzyme encoding genes. Also substrate utilization in these strains is altered and suggests an interconnection between the capability for sexual development and the detection and utilization of nutrients in their environment.