Comparative Genomics Of Magnaporthe Species From Different Host Plants

Rice blast disease,caused by filamentous fungus Magnaporthe oryzae,is a main disease to rice.This pathogen can not only infect rice but also infect barly,wheat and other crops,which made it a great threat to food security.To elucidate the evolutionary relationship between isolates of Magnaporthe species from different host plants and to identify genes or regions of the genome with significant variations.we compared several isolates from different host plants morphologically and genetically.our morphological assessment shows that,though,these isolates are highly host-specific,they still retain their indentity as Magnaporthe species.We further conducted phylogenetic analysis based on whole genome SNP sequences and subsequently,constructed phylogenetic tree.Findigs from the investigation shows that rice isolates are more closer to isolates from Setaria spp in evolution.however,isolates from Eleusine shows an independent evolution path compared with other isolates.SNPs was inhomogenously distributed in the whole genome,suggesting different regions of the genome might have natural selection pressure in unequal proportion.The comparison of carbon metabolism related genes in three kinds of Magnaporthaceae pathogens,including Magnaporthe oryzae,Magnaporthe poae,Gaeumannomyces graminis var.tritici,shows that isolates co-evolved a corresponding mode of nutrition and metabolism stratgies in response to the different way of life and the host.The rapid evolution of secreted proteins can help isolates evade host defense system and adapted to different host environment quickly.By comparing secretome of different isolates,we found isolates from different plant host evolved a series of specific secreted proteins.Also,we obtained isolates specific secreted protein sequences of the grasses isolates and rice isolates,these specific secreted proteins can enhance our understaning of the host specificity of Magnaporthe.The chromosome distribution of these isolates' specific secreted proteins were mainly located in the telomere region.Transposon elements play an important role in genome evolution of asexual reproduction pathogens.We found quantity and variety of TEs significantly reduced in the grass blast,which make genome of grass blast relatively more stable.And we infer this reducement in grass blast may be caused by the long-term interactions with the host and the selective pressure from host.TEs research reveals the rapid variation of rice isolates and rapid increases of virulence frequency.The analysis of evolution pattern of AVR genes in different isolates show different AVR genes may have different origins and evolution ways.Avr1-C039 was originated from grass isolates,but deleted by two possible mechanisms in the rice blast.AvrPiz-t was also originated from grass blast,its evolution process is very slow.And orthologous fragments from grass blast can restore avirulence of rice blast.Other AVR genes,such as AvrPia,AvrPii,which show highly polymorphism,may be evolved on rice blast.In conclusion,our research revealed the phylogenetic relationship between Magnaporthe species' isolates from different plant hosts.Elucidated the TEs and quickly losing or recombining of telemore region are important to help M.oryzae adapt to the new host.And identified the evolution models of some avirulent genes.