Novel <i>ToxA</i> Insertion Element in <i>Pyrenophora tritici-repentis</i>

Pyrenophora tritici-repentis is the causative agent of tan spot in wheat. Among the necrotrophic effectors produced by the fungus, the most studied is the necrosis-inducing protein toxin Ptr ToxA, encoded by the ToxA gene. Previously, we identified 10 strains of P. tritici-repentis from Kazakhstan and Russia, the amplified fragment of which with ToxA-specific primers turned out to be larger than expected. Sequencing of these fragments of three P. tritici-repentis strains revealed the presence of a 170 bp insertion element PtrHp2 located in exon 2 of the ToxA gene. The PtrHp2 sequence includes three pairs of mutually complementary regions of 16, 8 and 6 bp in length, forming a hairpin-type secondary structure. The inability of P. tritici-repentis strains possessing PtrHp2 in the ToxA gene to cause necrosis on the leaves of cv. Glenlea, which differentiates the presence of Ptr ToxA in the pathogen has been established. This fact indicates a violation of the expression of the mutant ToxA gene. However, the mutant ToxA gene with PtrHp2 is retained in 45% of the fungal mitotic progeny. The fragments homologous to the PtrHp2 are found in non-coding parts of ToxB gene and its homologues in P. tritici-repentis strains, as well as in the genomes of other fungi. This observation indicates the transposon nature of PtrHp2.