Induced Resistance And Molecular Mechanism Of Resistance Genes Associated To Two Kinds Of Cereal Aphids In 13 Winter Wheat Lines

Triticum aestivum L.is one of the staple crops with the largest planting area and the widest distribution range in the world.The English grain aphid Sitobion avenae(Fabricius)and the bird cherry-oat aphid Rhopalosiphum padi(Linnaeus)are two commonly occurring pests on cereal crops worldwide.The feeding behavior of aphids enable them to transmit the wheat virus,which seriously affect the quality and yield of wheat.In recent years,the global warming and the rapid change of farming systems had seriously increased the damage caused by cereal aphids.Currently,chemical spraying is the main strategy of controlling the aphid,but the series of negative effects induced by chemical pesticides have brought more serious challenges.Therefore,transferred the candidate genes with aphid resistance into elite wheat cultivars is considered the most economical,safety and effective measures to control cereal aphids.Accordingly,a large number of studies have been focused on identification the candidate gene and molecular mechanism related to Schizaphis graminam(Rondani)-resistance genes,and the remarkable results have been achieved.However,only a few studies focused on identification the candidate gene and molecular mechanism related to S.avenae and R.padi.Our previous studies revealed that winter wheat line XN98-10-35 is resistant to cereal aphids.In addition,the candidate genes associated to S.avenae were mapped and identified,however,its molecular mechanism is not clear.Based on this,we used the techniques and methods of insect ecology and molecular biology to identify and evaluate the resistance level of wheat line XN98-10-30 and the separation of XN98-10-35 to cereal aphids.In addition,the mechanism of aphid resistance was explored and the candidate genes of aphid were verified.The important conclusions are as follows:1.Under controlled greenhouse conditions,the aphid index values of 13 varieties/lines were calculated according to the number of R.padi that had colonized the plants.Line 35-E4 exhibited the strongest resistance to R.padi(aphid index: 0.509,MR),Line 35-A20 exhibited the medium sensitive to R.padi(aphid index: 1.337,MS),while XN1376 was the most susceptible(aphid index: 1.675,HS).In the aphid weight gain experiment,significant differences in the average weight difference of each variety/lines were detected after seven days of consecutive feeding.The study was found that the stronger of the resistance,the more unfavorable the accumulation of aphids weight.The resistance level of wheat lines was negatively correlated with the weight accumulation of aphids.2.Herbivore infestation induces salicylic acid(SA)-or jasmonic acid(JA)-dependent responses in host plants.This study focused on determining the relative expression levels of the genes associated with these pathways in two near isogenic winter wheat lines,35-E4 and 35-A20,when attacked by R.padi(Linnaeus)and/or S.avenae(Fabricius).Infestation with either R.padi or S.avenae significantly up-regulated the expression of genes related to the SA-and JA-dependent pathways in these winter wheat lines.In the R.padi-resistant wheat line 35-E4,R.padi infestation,JA or SA spraying and mechanical wounding all significantly increased the relative expression of plant pathogenesis-related protein 1(PR-1)at all sampling times.Furthermore,the expression levels of the lipoxygenase(LOX)and allene oxide synthase(AOS)genes increased 4.5-fold and 10.0-fold,respectively,at 0 h after R.padi attack.In the R.padisusceptible wheat line 35-A20,infestation with either R.padi or S.avenae increased the expression levels of the AOS and phenylalanine ammonia-lyase(PAL)genes.In sequential aphid infestation experiments,the expression levels of the AOS gene increased more than in a single-species aphid infestation.However,the expression level of the PAL gene was antagonistically affected by the initial infestation and was reduced in secondary S.avenae and R.padi infestations.Overall,these results showed that aphid infestation induced host JA-and SA-dependent responses in host plants;however,the expression profiles of these genes in resistant and susceptible host lines were significantly different.3.In study of field tests,the wheat lines XN98-10-30 and the 11 separation of XN98-10-35 infested with the S.avenae or R.padi,its 1000-kernel weight decrease rate is lower,and the difference is significant.Meanwhile,the 1000-kernel weight decrease rate of wheat lines attackd by S.avenae were higher than R.padi.The above results revealed that XN98-10-30 and the 11 separation of XN98-10-35 exhibited a higher level of tolerance to S.avenae and R.padi infestation than XN1376.4.The study had cloned and analyzed the EST sequences of 5 candidate genes in wheat XN1376,35-E4,35-A20,35-2A and 35-Q10 R from the DNA level.The results showed that the nucleotide sequences of the candidate gene1 associated to aphid resistance was different from that of XN1376.5.The expression patterns of 5 resistance candidate EST sequences were analyzed in 13 wheat lines.The results showed that the relative expression of five EST sequences in most wheat lines was significantly higher than XN1376 in the separation of XN98-10-35.The expression profiles of genes related to synthesis of wheat carbohydrate was studied in wheat lines XN1376,35-E4 and 35-A20.The results revealed that the seven genes related to sucrose synthase and starch synthase were up-regulated in the flag leaves of separation lines of XN98-10-35.Thus,the resistant category of aphid resistance mechanism of lines XN98-10-35 was the tolerance.