The transcriptome of lae1 mutants of Trichoderma reesei cultivated at constant growth rates reveals new targets of LAE1 function
1 Department of Biochemical Engineering, Faculty of Science and Technology, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary
2 Institute of Chemical Engineering, University of Technology of Vienna, Gumpendorferstrasse 1a A-1060 Vienna, Austria
3 Department of Human Genetics, Faculty of Medicine, University of Debrecen, Nagyerdei krt. 98, H-4032 Debrecen, Hungary
4 Roche Hungary Ltd., Edison u. 1, H-2040 Budaörs, Hungary
5 Austrian Center of Industrial Biotechnology (ACIB), Petersgasse 12, A-8010 Graz, Austria
BMC Genomics 2014, 15:447 doi:10.1186/1471-2164-15-447Published: 9 June 2014
The putative methyltransferase LaeA is a global regulator that affects the expression of multiple secondary metabolite gene clusters in several fungi. In Trichoderma reesei, its ortholog LAE1 appears to predominantly regulate genes involved in increasing competitive fitness in its environment, including expression of cellulases and polysaccharide hydrolases. A drawback in all studies related to LaeA/LAE1 function so far, however, is that the respective loss-of-function and overexpressing mutants display different growth rates. Thus some of the properties attributed to LaeA/LAE1 could be simply due to changes of the growth rate.
We cultivated T. reesei, a Δlae1 mutant and a lae1-overexpressing strain in chemostats on glucose at two different growth rates (0.075 and 0.020 h-1) which resemble growth rates at repressing and derepressing conditions, respectively. Under these conditions, the effect of modulating LAE1 expression was mainly visible in the Δlae1 mutant, whereas the overexpressing strain showed little differences to the parent strain. The effect on the expression of some gene categories identified earlier (polyketide synthases, heterokaryon incompatibility proteins, PTH11-receptors) was confirmed, but in addition GCN5-N-acetyltransferases, amino acid permeases and flavin monooxygenases were identified as so far unknown major targets of LAE1 action. LAE1 was also shown to interfere with the regulation of expression of several genes by the growth rate. About a tenth of the genes differentially expressed in the Δlae1 mutant under either growth condition were found to be clustered in the genome, but no specific gene group was associated with this phenomenon.
Our data show that – using T. reesei LAE1 as a model - the investigation of transcriptome in regulatory mutants at constant growth rates leads to new insights into the physiological roles of the respective regulator.