carbonum (designated race 2) completely lack all of the known biosynthetic genes [5, 8]. The TOX2 locus is meiotically unstable [10]. HC-toxin is an inhibitor of histone deacetylases (HDACs) of the RPD3
class [11, 12]. A chemically related HDAC inhibitor, apicidin, is made by Fusarium incarnatum (=F. semitectum) [13]. Like HC-toxin, apicidin is a cyclic tetrapeptide containing a D-imino acid and an L-amino acid with an aliphatic R-group (Aeo in the case of HC-toxin and 2-amino-8-oxo-decanoic acid in the case of apicidin). The gene cluster responsible for apicidin biosynthesis has been characterized, and Selleck BIBF-1120 many of the genes of the apicidin gene cluster have as their closest known homologs the genes of TOX2, including HTS1, TOXA, TOXE, and TOXF[14]. During a screen for new HDAC inhibitors, a new species of Alternaria (A. jesenskae) that produces HC-toxin was discovered [15]. VX-680 order A. jesenskae was isolated from seeds of Smad phosphorylation Fumana procumbens, a shrubby perennial with a wide geographic distribution, but it is not known if A. jesenskae is pathogenic. A situation in which two fungi in different genera produce the same compound is unusual and presents an opportunity to explore the evolution of a complex secondary metabolite, especially one with a strong evolutionary impact on the cereals. Here we document the identification and characterization of the genes for HC-toxin biosynthesis in A. jesenskae. Results Alternaria jesenskae produces HC-toxin
An isolate of A. jesenskae was obtained and its taxonomic identity confirmed by sequencing of the ITS regions [15]. Culture filtrates of A. jesenskae were fractionated by reverse phase HPLC.
No particular peak was seen at the retention time of HC-toxin (Figure 1A), but fractions with the same retention time as native HC-toxin contained an epoxide-containing compound with the same Rf on TLC as HC-toxin (Figure 1B). The mass of this compound was determined to be 437.2407 ± 0.0007 ([M + H]+), compared to a calculated mass of 437.2400 for a compound with the elemental composition of HC-toxin (C21H32N4O6) [16]. These results confirm the observation that A. jesenskae makes HC-toxin. Figure 1 Aldehyde dehydrogenase Analysis of HC-toxin from A. jesenskae by HPLC and TLC. (A) HPLC of standard HC-toxin (10 μg). (B) HPLC of A. jesenskae culture filtrate extracted with dichloromethane (400 μl equivalent crude culture filtrate). Detection in both cases was at 230 nm. (C) TLC of (1) native HC-toxin, and (2) material from A. jesenskae eluting between 8 and 10 min from HPLC of the separation shown in panel B. Visualization used an epoxide-specific reagent [45]. The asterisk indicates the position of HC-toxin. Alternaria jesenskae has unmistakable orthologs of the TOX2 genes The genome of A. jesenskae was determined to ~10× coverage by pyrosequencing followed by assembly. Using BLASTN and TBLASTN, strongly related sequences of each of the known seven TOX2 genes from C. carbonum were found in the genome of A. jesenskae (Table 1).