Identification Of Resistance To Green Peach Aphids Of Shouxing Peach And Its Molecular Mechanism

Peach?Prunus persica?L.?Batsch?is a deciduous fruit tree originated in China and cultivated around the world.It has been cultivated for over 3,000 years in China.Green peach aphid?GPA,Myzus persicae Sülzer?is one of the most important pests negatively affecting the growth of peach trees in spring and parasitizeson peach tree for over wintering.At least three times chemical spraying must be carried out for GPA control every year,which increases the cost of materials and labors,also the risk of food safety and ecological hazards.The cultivation and application of resistant plants is considered the most economical and effective way to control related insect pests and diseases.In this regard,the exploration of resistant resources and the study of its mechanism are the basis of other work.To date,several peach germplasm resources with aphid-resistant have been identified.Rubira,Weeping Flower Peach and P1908?Prunus davidiana?were identified and charactered from the resource repository in Avignon Centre of French Academy of Agricultural Sciences,and the heredity and genetic locus of resistance to these resources were studied extensively.In China,three kinds of resistance resources,Shouxing peach,Prunus davidiana and flowering peach,were also screened from Zhengzhou Peach Germplasm Repository,but no follow-up study was done.In this study,several hybrid groups originated from Shouxing peach were created and evaluated for restistance to green peach aphids.The inheritance was analysed and the gene was mapped by combining multiple molecular markers.The molecular response of resistant/susceptible populations to aphid infection was analyzed by transcriptome analysis.The main results were as follows:1.The resistance of Shouxing peach to GPA is controlled by a single dominate geneShouxing peach showed evident antixenosis to GPA.After 1-3 days of artificial inoculation,aphids gradually left the plants.Water-stained spots appeared in the penetration site,and then turned deep red several days later.The red spots were the unique characteristics of resistant plants.The resistance/susceptibility to aphidsin the hybridized progenies showed bimodal distribution,and the segregation ratio accorded with Mendelian genetic segregation ratio.The phenotype of resistance to GPA in peach was stable in the 6th generation of hybrid isolation population,and no obvious changes in the virulence of aphids were found.Population linkage analysis showed that there was no linkage between GPA resistance and dwarfism,but there was a significant linkage between GPA resistance and white/yellow fruit flesh color.2.The aphid-resistant gene Rm3 was located in a physical regionof 160 Kb at the bottom of peach chromosome 1,and a candidate gene was found.141 seedlings from 01-77-3 ×CN 13 and 116 seedlings from 96-5-1 × 10-7 were used as the positioning population.SNP primers were designed based on the peach reference genome.The resistance gene was initially located between Pp01₃8011783 and Pp01₄7231340,and the genetic distance was about 9.22 Mb.Combining with parental resequencing data,the primers were designed every 200 Kb in the initial localization interval,and the target gene were located between 45.66 Mb and 46.12 Mb on chromosome 1 by HRM and Sanger sequencing.In order to locate the target gene more accurately,InDel and SSR markers were developed in the localization interval.Finally,the gene was located between 45.676 and 45.837 Mb with a physical distance of 160 Kb,between gene Prupe.1G559300 and Prupe.1G561200.There are 21 genes in the final fine mapping interval.And twelve genes were identified by transcriptome analysis,but no changes were found in the expression level.A resistance gene ppa00596 m was found in this interval.A pair of primers was developed to clone it from resistant and susceptible seedlings.But a whole new NBS-LRR gene was found from resistant seedlings.This gene differentially expressed in resistant and susceptible seedlings after infection by GPA.This gene maybe the candidate gene for PpRm3.3.Rm3 resistance is induced by aphid infection.The resistance response to GPA involves biological stress,reactive oxygen species family,transcription factors,PR protein,and genes related to the synthesis of secondary metabolites including phenylalanine/flavonoids.To elucidate the molecular mechanism of peach resistance to GPA,aphids were inoculated on new shoots of resistant/susceptible aphid lines from the same segregation population.The new shoots of resistant/susceptible aphid lines were sampled for transcriptome sequencing analysis before infection and 3,6,9,12,24,48,72 hours after infection.A total of 3854 differentially expressed genes were identified.The changes of gene expression patterns at transcriptional level of the two genotypes were significantly different.Compared with the aphid-susceptible materials,the expression of genes related to biological stress,reactive oxygen species,transcription factors,PR protein and secondary metabolites,including phenylalanine/flavonoids,in resistant materials was significantly up-regulated.These defense-related genes differentially expressed in resistant/susceptible genotypes provided basic data for clarifing the resistance mechanism in peach with Rm3 gene.