Cross-Pathway and Pathway-Specific Control of Amino Acid Biosynthesis in Magnaporthe grisea

The gene encoding the small subunit of the arginine-specific carbamoyl phosphate synthetase, ARG2, of Magnaporthe grisea was characterized to examine the basic regulation of biosynthetic genes in this plant pathogen. The transcript of the ARG2 gene contains an upstream open reading frame (uORF) that is similar to uORFs found in the homologous genes of Neurospora crassa (arg-2) and Saccharomyces cerevisiae (CPA1), suggesting that the M. grisea gene is translationally regulated by a mechanism that is conserved in these fungi. Amino acid imbalance leads to elevated levels of ARG2 mRNA, indicating that in addition to translational control, ARG2 is subject to cross-pathway transcriptional control. A DNA-binding activity that has properties similar to those of the global transcriptional regulator mediating cross-pathway control in N. crassa was detected in M. grisea cell extracts. Thus, it appears that both specific regulation of ARG2 by arginine and global regulation of amino acid biosynthesis are present in M. grisea and highly conserved among M. grisea, N. crassa, and S. cerevisiae.