Characterization of the Multiple-Copy Host-Selective Toxin Gene, ToxB, in Pathogenic and Nonpathogenic Isolates of Pyrenophora tritici-repentis

Abstract

ToxB, a gene that encodes a 6.6-kDa host-selective toxin (HST), is present in several races of the wheat pathogen Pyrenophora tritici-repentis. To learn more about the multiple ToxB open reading frames (ORFs), six of the estimated nine copies from a race 5 isolate were cloned and analyzed. All six copies of ToxB have identical 261-bp ORFs and thus encode the same form of Ptr ToxB. Sequence analysis of regions flanking the cloned ToxB loci revealed that the majority of loci are associated with portions of retrotransposons and a transposon-like sequence. Data indicate that ToxB loci reside on two chromosomes, 3.5 and 2.7 Mb, with the majority of copies located on the 2.7 Mb chromosome. A related gene, referred to as toxb, from a nonpathogenic race 4 isolate was also cloned and characterized. This is interesting because, until now, HST genes have only been found in toxin-producing, pathogenic isolates of plant pathogenic fungi. The toxb gene from nonpathogenic isolates is 86% similar to ToxB, and data suggest that toxb is a single-copy gene. No toxb transcript was detected under culture conditions that favor the expression of ToxB; therefore, these genes differ in their transcriptional regulation.

GliZ, a Transcriptional Regulator of Gliotoxin Biosynthesis, Contributes to Aspergillus fumigatus Virulence

“…However, many of these metabolites have tremendous importance to humankind, in that they display a broad range of useful antibiotic and pharmaceutical activities as well as less desirable immunosuppressant and toxic activities (49). Although several fungal toxins have been shown to be involved in plant pathogenesis (1,24,45,48), an unambiguous role of fungal toxins in human disease has yet to be established, with the exception of mycotoxin and mushroom ingestion. The present study is the first to demonstrate that A. fumigatus gliotoxin plays a role in mediating human neutrophil apoptosis ex vivo.…”

Solution NMR Structures of Pyrenophora tritici-repentis ToxB and Its Inactive Homolog Reveal Potential Determinants of Toxin Activity

“…Disulfide Bond Stability-Sequence comparison of mature ToxB and toxb shows 78% identity (27), with conservation of 51 amino acids including four cysteines that form two disulfide bonds (Fig. 1A).…”

Pyrenophora tritici-repentis, Causal Agent of Tan Spot: A Review of Intraspecific Genetic Diversity

“…In this case of Ptr Tox B is encoded by the multiple copy of ToxB gene (Martinez et al, 2001(Martinez et al, , 2004Strelkov et al, 2006). It is know that the races 3 and 4 have present in their genomes singles copies of distinct ToxB homolog (Martinez et al, 2004;Strelkov et al, 2006). Therefore found P. triticirepentis strains carrying the ToxB gene but without production of Ptr ToxB were found (Andrie et al, 2007;Lamari et al, 1995;Martinez et al, 2004;Strelkov et al, 2006).…”

“…The races 5, 6, 7 and 8 produce chlorosis in Katepwa and 6B662. In this case of Ptr Tox B is encoded by the multiple copy of ToxB gene (Martinez et al, 2001(Martinez et al, , 2004Strelkov et al, 2006). It is know that the races 3 and 4 have present in their genomes singles copies of distinct ToxB homolog (Martinez et al, 2004;Strelkov et al, 2006).…”

“…It is know that the races 3 and 4 have present in their genomes singles copies of distinct ToxB homolog (Martinez et al, 2004;Strelkov et al, 2006). Therefore found P. triticirepentis strains carrying the ToxB gene but without production of Ptr ToxB were found (Andrie et al, 2007;Lamari et al, 1995;Martinez et al, 2004;Strelkov et al, 2006). In this way and considering that the virulence patterns of the various P. tritici-repentis isolates are based in that each compatible interaction host-pathogen that it is mediated by HST ; Andrie et al, (2007) suggested that the use of PCR multiplex is appropriated to corroborate the phenotypic identification of P. tritici-repentis races.…”