Studies On The Polygenic Genetic Basis Of Interaction Between Oryza Sativa And Magnaporthe Grisea

Revealing the genetic basis of interaction between plant and pathogen would provide the theoretical foundation for understanding the mechanisms of plant resistance and pathogen pathogenesis and breeding crop varieties with durable and broad-spectrum resistance.Plant-pathogen interaction is a complicated biochemical and physiological process,in which many genes in plant and pathogen genomes are involved.Therefore,simultaneous analysis of plant and pathogen genomes is needed for full understanding of the internal mechanisms of plant-pathogen interaction.With rice blast as a model,this study aimed to reveal the across-species polygenic system controlling the interaction between rice and Magnaporthe grisea by scanning for related QTLs/genes in the rice and M.grisea genomes simulataneously,using the recently proposed QTL mapping method for plant-pathogen interaction,which takes the plant and pathogen as an integrated system,and combining QTL analysis with gene expression data.The main contents and results are as follows:1.A cross between two M.grisea strains,Guy11 and 2539,was performed and 229 progeny strains were obtained by randomly isolating ascospores.By inoculating this population on rice cultivar CO39,it was comfirmed that the avirulence of 2539 to CO39 was controlled by the avirulence gene AVR1-CO39.After inoculating this population on other 14 rice cultivars,it was found that 8 rice cultivars showed the same responses to the inoculations as CO39,suggesting that the avirulence of 2539 to these 8 cultivars should be also controlled by AVR1-CO39;the responses of the other 6 rice cultivars were also similar to CO39,suggesting that the avirulence of 2539 to these 6 cultivars might be controlled by different avirulence genes other than but closely linked to AVR1-CO39,and linkage analysis indicated that these gene are located around AVR1-CO39 within a range of 30kb.2.Based on the released genome sequence data of M.grisea,we designed primers for 446 simple sequence repeat(SSR)loci.426 pairs of primers could obtain amplification products,of which 314 pairs showed polymorphisms among 9 M. grisea strains isolated from rice(including a laboratory strain 2539).The polymorphism percentage is 73.9%.The number of alleles of each SSR marker ranged 2～9 with an average of 3.3.The polymorphic information content(PIC)of each marker ranged 0.20～0.89 with an average of 0.530.3.Using the progeny population of Guy11×2539,a genetic map of M.grisea consisting of 176 SSR markers was constructed.The map covers a total length of 1247 cM with an average distance of 7.1 cM between adjacent markers,equivalent to a physical length of about 35.0 Mb or 93%of the genome.Among these SSR markers, 26(14.4%)markers showed the genetic segregation distortion at the 1%significance level.Among them,16 markers deviated toward Guy11 and 10 markers deviated toward 2539.4.Comparison between the genetic map and the physical map indicated that the positions of five markers were not consistent in the two maps.Eleven markers with unknown physical positions were mapped in the genetic map.In the M.grisea genome,1cM is approximately equivalent to 28kb on average.Some recombination hot spots and cold spots were identified.5.For the convenience of readers to utilize the SSR markers developed in this study,we have established a web-based database named MGM,which is accessible at website http://ibi.zju.edu.cn/pgl/MGM/index.html.Detailed information of each SSR is provided,including position,primers,repeat motif,expected PCR product length, anneal temperature,number of alleles detected in the nine M.grisea isolates and PIC value.6.One hundred and twenty-one progeny strains of Guy11×2539 not carrying AVR1-CO39 were used to randomly inoculate 131 recombinant inbred lines(RILs) derived from a cross between two indica rice cultivars,Acc8558 and H359.With relative lesion area(RLA)and disease grade(DG)as index,QTL mapping was performed for rice-M,grisea interaction in both the rice and the M.grisea genomes simultenously.Three and two QTLs underlying RLA were detected in the rice genome and the M.grisea genome,respectively,of which a QTL of rice was found to interact with a QTL of M.grisea.Four QTLs each conferring DG were found in the rice genome and the M.grisea genome,respectively.Epistatic effects were detected between one pair of QTLs in rice and three pairs of QTLs in M.grisea.7.The positional interval of each QTL in the physical map of rice and M.grisea was identified according to their released genome sequences,and was compared with the microarray and EST data.Five candidate genes were found for 4 rice QTLs and 9 candidate genes were found for 5 M.grisea QTLs.