Fungi are eukaryotic microorganisms that influence our everyday lives in areas as diverse as agriculture, medicine and basic science. With the advent of molecular biology, it has been attempted to improve the expression level of heterologous genes, which encode favorable traits in fungal strains. The expression of heterologous genes can be limited in transcription, post-transcription, translation and post-translation levels. Several genetic strategies have been developed to reduce the expression constrains and to enhance genes functionality. Among these strategies can be pointed to the introduction of multicopies of the desired gene, change of AT-rich sequences, gene fusion with a well-expressed gene, the use of strong promoters and signal sequences, optimization of codon usage, the construction and use of protease-deficient and chaperones/foldases-overproduced strains and the use of native or artificial intron-containing genes. These strategies have often resulted in the expected increase in the expression of heterologus genes. With the isolation of a large number of genes encoding desired traits and the availability of a large collection of wild isolates, the improvement of strains with a better functional performance would be possible.

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