Trichoderma reesei meiosis generates segmentally aneuploid progeny with higher xylanase-producing capability

Abstract

BackgroundHypocrea jecorina is the sexual form of the industrial workhorse fungus Trichoderma reesei that secretes cellulases and hemicellulases to degrade lignocellulosic biomass into simple sugars, such as glucose and xylose. H. jecorina CBS999.97 is the only T. reesei wild isolate strain that is sexually competent in laboratory conditions. It undergoes a heterothallic reproductive cycle and generates CBS999.97(1-1) and CBS999.97(1-2) haploids with MAT1-1 and MAT1-2 mating-type loci, respectively. T. reesei QM6a and its derivatives (RUT-C30 and QM9414) all have a MAT1-2 mating type locus, but they are female sterile. Sexual crossing of CBS999.97(1-1) with either CBS999.97(1-2) or QM6a produces fruiting bodies containing asci with 16 linearly arranged ascospores (the sexual spores specific to ascomycetes). This sexual crossing approach has created new opportunities for these biotechnologically important fungi.ResultsThrough genetic and genomic analyses, we show that the 16 ascospores are generated via meiosis followed by two rounds of postmeiotic mitosis. We also found that the haploid genomes of CBS999.97(1-2) and QM6a are similar to that of the ancestral T. reesei strain, whereas the CBS999.97(1-1) haploid genome contains a reciprocal arrangement between two scaffolds of the CBS999.97(1-2) genome. Due to sequence heterozygosity, most 16-spore asci (>90%) contain four or eight inviable ascospores and an equal number of segmentally aneuploid (SAN) ascospores. The viable SAN progeny produced higher levels of xylanases and white conidia due to segmental duplication and deletion, respectively. Moreover, they readily lost the duplicated segment approximately two weeks after germination. With better lignocellulosic biomass degradation capability, these SAN progeny gain adaptive advantages to the natural environment, especially in the early phase of colonization.ConclusionsOur results have not only further elucidated T. reesei evolution and sexual development, but also provided new perspectives for improving T. reesei industrial strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0202-6) contains supplementary material, which is available to authorized users.

Proximity ligation scaffolding and comparison of two Trichoderma reesei strains genomes

“…The same pipeline was applied to the QM6a-derived strain Rut-C30, resulting in a genome scaffold in perfect agreement with previously identified chromosomal rearrangements between the two genomes [14, 15]. This result prompts us to put forward predictive karyotypes for several other T. reesei strains and to discuss the impact of such karyotypes on the emergence of segmental aneuploidy during crossing experiments [10]. …”

Genomics insights into different cellobiose hydrolysis activities in two Trichoderma hamatum strains

“…For example, under cellulase-inducing conditions, the production of secreted β-glucosidase comprises only about 1% of the total T . reesei cellulase [14], indicating that the hydrolysis of cellobiose constitutes a rate-limiting step during the enzymatic processing of cellulose [15, 16]. Although commercial cellulase is available, many of the most well-known biomass- degrading fungi display low β-glucosidase (cellobiose) activity, thus the initial bioconversion of biomass to sugars remains a key bottleneck in the process of biofuel production.…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…Interestingly, in T. reesei (teleomorph Hypocrea jecorina), sexual development results in fertilized perithecia embedded in stromata containing decahexads with 16 ascospores per ascus (859). Recently, we showed that the 16 ascospores are generated by one round of meiosis followed by two rounds of postmeiotic mitosis (1108).…”