Mutation Analysis Among Field Isolates Of Magnaporthe Oryzae Through Genome Resequencing

Rice blast caused by Magnaporthe oryzae is one of the most destructive diseases in rice, which seriously restricts rice production in the world. Whole genome sequencing for M. oryzae has been finished using a laboratory strain 70-15 which is derived from a sexual cross between Guy 11 (a French Guiana field strain) and an isolate from weeping lovegrass. Although 70-15 is still widely used and its host range, physiology characteristics and genetic background have been well studied, it is always not a strongly representative rice-infecting isolate.In order to clearly uncover the genome variation features of natural field rice-infecting isolates, two Chinese field isolates FJ81278 from Fujian and HN19311 from Hunan were sequenced by next-generation sequence (NGS).Comparative genomics analysis results revealed that FJ81278 contained totally about 1.75 Mb unique contigs and 118 novel genes were predicted in them, among which 27 genes were considered to be candidate effectors and some other genes possessed high homology to pathogenesis related genes in other fungi. According to the genetic polymorphisms between these two isolates, almost all SNP sites were located in protein-encoding regions and on average there would be one SNP site every 4000 bp. This phenomenon seemed to be related with that asexual reproduction is absolutely dominant in the life cycle of M. oryzae and the genetic variations in its genome were always caused by spontaneous mutations.Moreover, on the basis of known features of cloned avirulence genes, some potential effectors or secreted proteins involved in recognition and interaction with host were identified through whole-genomg-comparative analysis of polymorphisms in predicted secreted proteins among different isolates.Finally, highly variable HET locus which may function in heterokaryon incompatibility process and SET gene family which is related to histone acetylation in M. oryzae population were proposed through analysis of positive selection sites among different rice-infecting isolates and wheat-infecting isolates. Both genes might play an important role in host specificity of M. oryzae.