Transformation System for Hypocrea jecorina ( Trichoderma reesei ) That Favors Homologous Integration and Employs Reusable Bidirectionally Selectable Markers

Hypocrea jecorina is an industrially important filamentous fungus due to its effective production of hydrolytic enzymes. It has received increasing interest because of its ability to convert lignocellulosic biomass to monomeric sugars, which can be converted into biofuels or platform chemicals. Genetic engineering of strains is a highly important means of meeting the requirements of tailor-made applications. Therefore, we report the development of a transformation system that allows highly efficient gene targeting by using a tmus53 (human LIG4 homolog) deletion strain. Moreover, it permits the unlimited reuse of the same marker by employing a Cre/loxP-based excision system. Both marker insertion and marker excision can be positively selected for by combining resistance to hygromycin B and loss of sensitivity to fluoroacetamide. Finally, the marker pyr4, also positively selectable for insertion and loss, can be used to remove the cre gene.