Functional studies of gene regulatory networks in Trichoderma reesei during the ce...
Understanding the role of the master regulator XYR1 in Trichoderma reesei by globa...
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Author(s): |
Augusto Savio Peixoto Ramos
Total Authors: 1
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Document type: | Doctoral Thesis |
Press: | São Paulo. |
Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
Defense date: | 2002-11-05 |
Examining board members: |
Hamza Fahmi Ali El Dorry;
Sérgio Verjovski de Almeida;
Maria Célia Bertolini;
Rogelio Lopes Brandão;
Francisco Gorgônio da Nobrega
|
Advisor: | Hamza Fahmi Ali El Dorry |
Abstract | |
The filamentous fungus Trichoderma reesei is a natural soil inhabitant capable of metabolizing a vast number of polysaccharide substrates. In this work, we describe two genes of T. reesei, named Trhxt1 and Trhxt2, which code for proteins with significant similarities to glucose transporters from other fungi. These genes were identified in an EST database of T. reesei. Sequence analysis of TrHXT1 and TrHXT2 revealed 12 putative transmembrane domains and several other characteristic motifs found in members of the major facilitator superfamily (MFS). Trhxt1 is transcriptionally induced only by low levels of glucose(≈ 100 µmol 1-1), while Trhxt2 expressionis independent of both glucose concentration and carbon source. We also show that Trhxt1 expression is enhanced when cells are exposured to low oxygen levels; in contrast, Trhxt2 expression seems to be repressed at these conditions. Glucose transport in T. reesei is apparently mediated by a multicomponent uptake system, in which the high-affiníty component has a Km of approximately 20 µmol 1-1. This low Km value is similar to the values reported for glucose uptake by other filamentous fungi. Kinetics of glucose transport in a T. reesei ΔTrhxt1 strain suggests that Trhxt1 is involved in glucose uptake in conditions of low glucose (≤ 100 µmol 1-1), which are most probably found in the soil, a low-nutrient environment. Interestingly, índuction ofthe T. reesei cellulase system by cellulose ís significantly delayed in the ΔTrhxt1 mutant, suggesting that glucose transport may be important to the mechanisms of expression of the cellulase genes. Finally, we hope that this work may be helpful to provide a better understanding of sugar uptake in filamentous fungi, for which there is little information available. (AU) |