Identification of New Genes Positively Regulated by <i>Tri10</i> and a Regulatory Network for Trichothecene Mycotoxin Production

Tri10, a regulatory gene in trichothecene mycotoxin-producing Fusarium species, is required for trichothecene biosynthesis and the coordinated expression of four trichothecene pathway-specific genes (Tri4, Tri5, Tri6, and Tri101) and the isoprenoid biosynthetic gene for farnesyl pyrophosphate synthetase (FPPS). We showed that six more trichothecene genes (Tri3, Tri7, Tri8, Tri9, Tri11, and Tri12) are regulated by Tri10. We also constructed a cDNA library from a strain of Fusarium sporotrichioides that overexpresses Tri10 ( upward arrow Tri10) and used cDNA derived from the upward arrow Tri10 strain and a non-Tri10-expressing strain (DeltaTri10) to differentially screen macroarrays prepared from the cDNA library. This screen identified 15 additional Tri10-regulated transcripts. Four of these transcripts represent Tri1, Tri13, and Tri14 and a gene designated Tri15. Three other sequences are putative orthologs of genes for isoprenoid biosynthesis, the primary metabolic pathway preceding trichothecene biosynthesis. The remaining eight sequences have been designated Ibt (influenced by Tri10) genes. Of the 26 transcripts now known to be positively regulated by Tri10, 22 are positively coregulated by Tri6, a gene that encodes a previously characterized trichothecene pathway-specific transcription factor. These 22 Tri10- and Tri6-coregulated sequences include all of the known Tri genes (except for Tri10), the FPPS gene, and the other three putative isoprenoid biosynthetic genes. Tri6 also regulates a transcript that is not regulated by Tri10. Thus, Tri10 and Tri6 regulate overlapping sets of genes that include a common group of multiple genes for both primary and secondary metabolism.