The VELVET A orthologue VEL1 of Trichoderma reesei regulates fungal development and is essential for cellulase gene expression.

Razieh Karimi Aghcheh,Zoltán Németh,Benigno Aquino,Melinda Paholcsek,Levente Karaffa,Christian P Kubicek,Erzsébet Fekete,Lea Atanasova,Erzsébet Sándor,Irina S Druzhinina

doi:10.1371/journal.pone.0112799

Razieh Karimi Aghcheh, Zoltán Németh + Show 8 more

Open Access

https://doi.org/10.1371/journal.pone.0112799

Copy DOI

Abstract

Trichoderma reesei is the industrial producer of cellulases and hemicellulases for biorefinery processes. Their expression is obligatorily dependent on the function of the protein methyltransferase LAE1. The Aspergillus nidulans orthologue of LAE1 - LaeA - is part of the VELVET protein complex consisting of LaeA, VeA and VelB that regulates secondary metabolism and sexual as well as asexual reproduction. Here we have therefore investigated the function of VEL1, the T. reesei orthologue of A. nidulans VeA. Deletion of the T. reesei vel1 locus causes a complete and light-independent loss of conidiation, and impairs formation of perithecia. Deletion of vel1 also alters hyphal morphology towards hyperbranching and formation of thicker filaments, and with consequently reduced growth rates. Growth on lactose as a sole carbon source, however, is even more strongly reduced and growth on cellulose as a sole carbon source eliminated. Consistent with these findings, deletion of vel1 completely impaired the expression of cellulases, xylanases and the cellulase regulator XYR1 on lactose as a cellulase inducing carbon source, but also in resting mycelia with sophorose as inducer. Our data show that in T. reesei VEL1 controls sexual and asexual development, and this effect is independent of light. VEL1 is also essential for cellulase gene expression, which is consistent with the assumption that their regulation by LAE1 occurs by the VELVET complex.

Highlights

Cellulose and hemicelluloses form the major amount of plant biomass and represent the largest reservoir of renewable carbon sources on Earth, which could potentially replace fuels and refinery products derived from fossil carbon components [1]
We have explored the function of the velvet gene vel1 of T. reesei
The most striking example is asexual sporulation, a trait influenced by VeA/VelA/VEL1 in all fungi: whereas a veA/velA knock out in A. nidulans, P. chrysogenum and N. crassa increases conidiation [29,38,39], it results in decreased conidiation in the corresponding knock-out mutants of A. fumigatus, A. parasiticus, A. flavus, Fusarium fujikuroi, F. graminearum, Dothistroma septosporum and T. virens [19,22,27,39,40,41,42,43,44]

Summary

Introduction

Cellulose and hemicelluloses form the major amount of plant biomass and represent the largest reservoir of renewable carbon sources on Earth, which could potentially replace fuels and refinery products derived from fossil carbon components [1]. We have recently shown that the expression of genes for lignocellulose degradation in T. reesei is further obligatorily dependent on the function of the protein methyltransferase LAE1 [9], the orthologue of the A. nidulans regulator of secondary metabolism and development LaeA [10]. This regulation requires a functional xyr, but a lae loss-of-function cannot be rescued by xyr overexpression [9], which would be consistent with the hypothesis that LaeA acts by removing the repressive chromatin [11]. The mechanism of LAE1-dependence of cellulase gene expression remains enigmatic

Methods

Results

Conclusion