Novel haplotypes and networks of AVR-Pik alleles in Magnaporthe oryzae

Abstract Li J, Wang Q, Li C, Bi Y, Fu X, Wang R. 2018. Novel haplotypes and networks of AVR-Pik alleles in Magnaporthe oryzae. PLoS Pathog _______. Rice blast disease is one of the most destructive fungal diseases of rice world-wide. The avirulence (AVR) genes of Magnaporthe oryzae are recognized by the cognate resistance (R) genes of rice, and trigger race specific resistance. Here, we studied the possible evolutionary pathways in the evolution of AVR-Pik alleles by analyzing the DNA sequence variation and assayed for their avirulence function to the cognate Pik alleles resistance genes under field conditions in China. Results of PCR products showed that 278 isolates of M. oryzae carry AVR-Pik alleles among genomic DNA of 366 isolates of M. oryzae collected from Yunnan Province, China. Among of them, 66.7-90.3% of M. oryzae carry AVR-Pik alleles from six regions of Yunnan. Moreover, 10 AVR-Pik haplotypes encoding five novel AVR-Pik variants were identified among 201 isolates. The AVR-Pik alleles stepwise evolved to virulence from avirulent forms via base substitution. These findings demonstrate that AVR-Pik alleles are under positive selection and mutations are responsible for defeating race-specific resistance Pik alleles in nature. Author summaryThe interaction of resistance gene (R) of rice and avirulence (AVR) gene of rice blast fungi are belong to the gene-for-gene theory, the variation of AVR is one of the major reasons for generation new race. To detect the variation of AVR gene in isolates population of Magnaporthe oryzae collected from rice production fields, will helpful for evaluated the effectiveness of R gens in rice production areas. The Pik allele contained five R genes of Pik, Pikh, Pikp, Pikm and Piks, and the corresponding to the AVR genes of AVR-Pik/kh/kp/km/ks of M. oryzae. The Pik gene specifically recognizes and prevents infections by isolates of M. oryzae that contain AVR-Pik. The molecular variation of AVR-Pik alleles of M. oryzae and Pik alleles of rice remains unclear. Here we demonstrated that polymorphism and distribution of AVR-Pik alleles in Yunnan Province, China. By pathogenicity assays to detect function of the different haplotypes of AVR-Pik, for the first time we show detour and stepwise evolution of AVR-Pik alleles in rice production areas of Yunnan. The functional AVR-Pik possesses diversified sequence structures, and is under positive selection pressure in nature.