| Quantitative disease resistance in plants plays vital roles in defending against diverse pathogens,however,we know little about its molecular mechanisms.In this study,we performed QTL analyses to dissect the genetic loci conferring resistance using Arabidopsis-Pseudomonas syringae interaction system,following which we fine mapped a major QTL and performed gene cloning.The results of this study are as follows.(1)Using bioluminescence assay and colony detection respectively,we revealed that the growth distribution of ES4326-lux(lux tagged Pseudomonas syringae pv.maculicola ES4326)in leaves of Col-0 and Aa-0 is influenced by air relative humidity after inoculation,and the growth of ES4326-lux in non-injection region of leaves in Aa-0 is influenced by the initial bacterial amount.(2)Next,in a fixed system,we revealed natural variation in disease resistance between Col-0 and Aa-0 against ES4326-lux and DC3000-lux(lux tagged Pseudomonas syringae pv.tomato DC3000).Histological staining revealed that ROS,cell death,and callose deposition can be detected in both Col-0 and Aa-0 after ES4326-lux inoculation.qPCR results revealed that compared with mock inoculation,PR1 is highly induced in Aa-0 and Col-0 while PDF1.2 and VSP2 are not after ES4326-lux inoculation.(3)Using a new RILs(recombinant inbred lines)between Col-0 and Aa-0,we constructed a linkage map and then performed QTL analyses.Three major QTLs have been revealed conferring resistance to DC3000-lux:the first one locates between 5501226 and G009 in Chr.2,the second one between NGA8 and 9065019 in Chr.4,and the third one between 6502045 and NGA76 in Chr.5.Results also revealed one major QTL in Chr.3 between F20H23 and 2212069(named as Qpm3.1)confers resistance to ES4326-lux.(4)Using HIFs(heterogeneous inbred family),we validated the Qpm3.1.Histological staining revealed that both cell death and ROS can be detected in HIF8C(the HIF8 plants that show Col-0 genotype in Qpm3.1)while they can not be detected in HIF8A(the HIF8 plants that show Aa-0 genotype in Qpm3.1)after ES4326-lux inoculation.By qPCR analyses,we found that compared with mock inoculation,PR1 is highly induced in both HIF8A and HIF8C(much higher in HIF8A)while PDF1.2 and VSP2 are not after ES4326-lux inoculation.(5)Using QTL analyses and HIFs,we demonstrated that Qpm3.1 also confers resistance to DC3000-lux-hopW1-1.And results revealed that the growth of DC3000-lux-hopW1-1 in HIF8A is influenced by the initial bacterial amount.Histological staining revealed that cell death can be detected in HIF8C and HIF8A after DC3000-lux-pME6031 or DC3000-lux-hopW1-1 inoculation.By qPCR analyses,we found that compared with DC3000-lux-pME6031,PR1 is highly induced in HIF8A and HIF8C(much faster and higher in HIF8A than in HIF8C)while PDF1.2 and VSP2 are repressed after DC3000-lux-hop W1-1 inoculation.(6)By QTL analyses,we found that Qpm3.1 has an epistatic effect when hopW1-1 is present on a major QTL Qpt1.1 conferring resistance to DC3000-lux in Gie-0 previously identified in our lab.(7)By fine mapping and genetic complementation of long genomic fragments in Aa-0,we confirmed three genes including At3g04610?At3g04620 and a new allele as candidate genes of Qpm3.1.Results also revealed that transformation of At3g04620 into HIF8C background has no effect on the phenotype of HIF8C.(8)qPCR results revealed that At3g04610 and At3g04620 are not induced in HIF8A after ES4326-lux or DC3000-lux-hopW1-1 inoculation.However,RT-PCR results revealed that the new allele is induced after DC3000-lux-hop W1-1 inoculation.These results obtained from this study will provide basis for the further research on the molecular mechanisms of quantitative resistance. |
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