First Detection of toxb2 Gene in Pyrenophora tritici-repentis Strains from Russia and Kazakhstan

For 18 Pyrenophora tritici-repentis strains the pathogenic micromycete causing tan spot of wheat, the race was determined and the ToxB/toxb genes were identified. The analyzed strains belonged predominantly to race 4, nonpathogenic for bread wheat. Alignment of the sequences of ToxB/toxb gene of one P. tritici-repentis strain from Kazakhstan and five strains from Tatarstan with the reference sequences of the ToxB1, toxb2, ToxB4, toxb12, and toxb14 genes allowed to accurately identify the genes analyzed in this study as toxb2. This is the first report of toxb2 gene in P. tritici-repentis populations from Russia and Kazakhstan. Also, the differences between the ToxB1 and toxb2 sequences were demonstrated: 27 nucleotide substitutions and one 3 bp deletion were found in the ORF region in ToxB1. In the 5’ UTR region of all obtained toxb2 sequences, as well as in reference ToxB1 sequences, the presence of four microsatellites (25 bp each) was detected between the TATA-box and the intron. In the toxb2 sequences of reference P. tritici-repentis strain SD20 and analyzed strains a 167 bp insertion was found in the 5’ UTR region before the intron. This insertion is not found in any known ToxB1 sequence and likely affects the functionality of toxb2 gene. Novel information on the structure of toxb2 gene has implications for understanding the evolution of ToxB/toxb genes of P. tritici-repentis.