AUTHOR=Wang Qun , Li Jinbin , Lu Lin , He Chengxing , Li Chengyun 

TITLE=Novel Variation and Evolution of AvrPiz-t of Magnaporthe oryzae in Field Isolates

JOURNAL=Frontiers in Genetics

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2020.00746

DOI=10.3389/fgene.2020.00746

ISSN=1664-8021

ABSTRACT=<p>The product of the avirulence (<italic>Avr</italic>) gene of <italic>Magnaporthe oryzae</italic> can be detected by the product of the corresponding resistance (<italic>R</italic>) gene of rice and activates immunity to rice mediated by the <italic>R</italic> gene. The high degree of variability of <italic>M. oryzae</italic> isolates in pathogenicity makes the control of rice blast difficult. That resistance of the <italic>R</italic> gene in rice has been lost has been ascribed to the instability of the <italic>Avr</italic> gene in <italic>M. oryzae</italic>. Further study on the variation of the <italic>Avr</italic> genes in <italic>M. oryze</italic> field isolates may yield valuable information on the durable and effective deployment of <italic>R</italic> genes in rice production areas. <italic>AvrPiz-t</italic> and <italic>Piz-t</italic> are a pair of valuable genes in the Rice-<italic>Magnaporthe</italic> pathosystem. <italic>AvrPiz-t</italic> is detectable by <italic>Piz-t</italic> and determines the effectiveness of <italic>Piz-t</italic>. To effectively deploy the <italic>R</italic> gene <italic>Piz-t</italic>, the distribution, variation, and evolution of the corresponding <italic>Avr</italic> gene <italic>AvrPiz-t</italic> were found among 312 <italic>M. oryzae</italic> isolates collected from Yunnan rice production areas of China. PCR amplification and pathogenicity assays of <italic>AvrPiz-t</italic> showed that 202 isolates (64.7%) held <italic>AvrPiz-t</italic> alleles and were avirulent to IRBLzt-T (holding <italic>Piz-t</italic>). There were 42.3–83.3% avirulent isolates containing <italic>AvrPiz-t</italic> among seven regions in Yunnan Province. Meanwhile, 11 haplotypes of <italic>AvrPiz-t</italic> encoding three novel <italic>AvrPiz-t</italic> variants were identified among 100 isolates. A 198 bps insertion homologous to solo-LTR of the retrotransposon inago2 in the promoter region of <italic>AvrPiz-t</italic> in one isolate and a frameshift mutation of CDS in another isolate were identified among 100 isolates, and those two isolates had evolved to virulent from avirulent. Synonymous mutation and non-AUG-initiated N-terminal extensions keeps the <italic>AvrPiz-t</italic> gene avirulence function in <italic>M. oryzae</italic> field isolates in Yunnan. A haplotype network showed that H3 was an ancestral haplotype. Structure variance for absence (28.2%) or partial fragment loss (71.8%) of <italic>AvrPiz-t</italic> was found among 39 virulent isolates and may cause the <italic>AvrPiz-t</italic> avirulence function to be lost. Overall, <italic>AvrPiz-t</italic> evolved to virulent from avirulent forms via point mutation, retrotransposon, shift mutation, and structure variance under field conditions.</p>