[Objectives]A codominance functional marker of the broad-spectrum bacterial blight resistance gene,Xa7,of rice was identified for accurate detection,generation tracking,and differentiation between homozygous and hemiz...[Objectives]A codominance functional marker of the broad-spectrum bacterial blight resistance gene,Xa7,of rice was identified for accurate detection,generation tracking,and differentiation between homozygous and hemizygous genotypes of the gene.[Methods]A potential functional marker containing four primers was designed using Premier 5 software and based on the differences on the sequences of Xa7,xa7,and allele-free genomes.The molecular distinctness of the marker in different materials was verified by PCR.Three crossbreed lines of Xa7 and their parents were inoculated with seven bacterial blight strains at the booting stage to examine the affected agronomic traits at maturation.[Results]The homozygous R084 of Xa7 could be amplified into a 91 bp band and the Nip free of allele with a 153 bp band,while the heterozygote Nip/R084,91 bp and 153 bp bands.The candidate codominance marker,Xa7fun,amplified fragments that matched the predicted target bands.No 91 bp fragment was amplified from 18 germplasms of varied types,indicating a lack of Xa7 in them.Whereas Ry1,Ry2 and Ry3 had a 91 bp band,suggesting the inclusion of homozygous Xa7.Under an elevated temperature,Huazhan responded to the seven bacterial blight pathogens as highly susceptible(HS),intermediate susceptible(MS),or susceptible(S);R084 to six of the seven pathogens(HNA1-4,FuJ,GDA2,GD1358,PX086,and YN24)as highly resistant(HR),intermediate resistant(MR)or resistant(R);Ry-1 to five pathogens(GDA2,HNA1-4,FuJ,GD1358,and YN24)as HR or MR;Ry-2 to five pathogens(GDA2,GD1358,HNA1-4,PXO86,and YN24)as HR or R;and Ry-3 to 6 pathogens(HNA1-4,FuJ,GDA2,GD1358,PXO86,and YN24)as HR or MR.Therefore,the infiltration of Xa7 in the improved crossbred lines RY-1,RY-2,and RY-3 significantly accentuated the blight resistance of Huazhan.[Conclusions]Homozygous or hemizygous Xa7 could be accurately differentiated by the currently identified codominance functional marker Xa7 fun.The Xa7 introgression did not significantly alter the critical agronomic traits in the hybridization from generation to generation and could be safely applied in breeding rice varieties with bacterial blight resistance.展开更多
Bacterial blight(BB)is a globally devastating rice disease caused by Xanthomonas oryzae pv.oryzae(Xoo).The use of disease resistance(R)genes in rice breeding is an effective and economical strategy for the control of ...Bacterial blight(BB)is a globally devastating rice disease caused by Xanthomonas oryzae pv.oryzae(Xoo).The use of disease resistance(R)genes in rice breeding is an effective and economical strategy for the control of this disease.Nevertheless,a majority of R genes lack durable resistance for long-term use under global warming conditions.Here,we report the isolation of a novel executor R gene,Xa7,that confers extremely durable,broad-spectrum,and heat-tolerant resistance to Xoo.The expression of Xa7 was induced by incompatible Xoo strains that secreted the transcription activator-like effector(TALE)AvrXa7 or PthXo3,which recognized effector binding elements(EBEs)in the Xa7 promoter.Furthermore,Xa7 induction was faster and stronger under high temperatures.Overexpression of Xa7 or co-transformation of Xa7 with avrXa7 triggered a hypersensitive response in plants.Constitutive expression of Xa7 activated a defense response in the absence of Xoo but inhibited the growth of transgenic rice plants.In addition,analysis of over 3000 rice varieties showed that the Xa7 locuswas found primarily in the indica and aus subgroups.A variation consisting of an 11-bp insertion and a base substitution(G to T)was found in EBEAvrXa7 in the tested varieties,resulting in a loss of Xa7 BB resistance.Through a decade of effort,we have identified an important BB resistance gene and characterized its distinctive interaction with Xoo strains;these findings will greatly facilitate research on the molecular mechanism of Xa7-mediated resistance and promote the use of this valuable gene in breeding.展开更多
Many plant disease resistance(R)genes function specifically in reaction to the presence of cognate effectors from a pathogen.Xanthomonas oryzae pathovar oryzae(Xoo)uses transcription activator-like effectors(TALes)to ...Many plant disease resistance(R)genes function specifically in reaction to the presence of cognate effectors from a pathogen.Xanthomonas oryzae pathovar oryzae(Xoo)uses transcription activator-like effectors(TALes)to target specific rice genes for expression,thereby promoting host susceptibility to bacterial blight.Here,we report the molecular characterization of Xa7,the cognate R gene to the TALes AvrXa7 and PthXo3,which target the rice major susceptibility gene SWEET14.Xa7 was mapped to a unique 74-kb region.Gene expression analysis of the region revealed a candidate gene that contained a putative AvrXa7 effector binding element(EBE)in its promoter and encoded a 113-amino-acid peptide of unknown function.Genome editing at the Xa7 locus rendered the plants susceptible to avrXa7-carrying Xoo strains.Both AvrXa7 and PthXo3 activated a GUS reporter gene fused with the EBE-containing Xa7 promoter in Nicotiana benthamiana.The EBE of Xa7 is a close mimic of the EBE of SWEET14 for TALe-induced disease susceptibility.Ectopic expression of Xa7 triggers cell death in N.benthamiana.Xa7 is prevalent in indica rice accessions from 3000 rice genomes.Xa7 appears to be an adaptation that protects against pathogen exploitation of SWEET14 and disease susceptibility.展开更多
基金Supported by Changde Science and Technology Transformation and Promotion Service Project[2019][CCN][0051-000].
文摘[Objectives]A codominance functional marker of the broad-spectrum bacterial blight resistance gene,Xa7,of rice was identified for accurate detection,generation tracking,and differentiation between homozygous and hemizygous genotypes of the gene.[Methods]A potential functional marker containing four primers was designed using Premier 5 software and based on the differences on the sequences of Xa7,xa7,and allele-free genomes.The molecular distinctness of the marker in different materials was verified by PCR.Three crossbreed lines of Xa7 and their parents were inoculated with seven bacterial blight strains at the booting stage to examine the affected agronomic traits at maturation.[Results]The homozygous R084 of Xa7 could be amplified into a 91 bp band and the Nip free of allele with a 153 bp band,while the heterozygote Nip/R084,91 bp and 153 bp bands.The candidate codominance marker,Xa7fun,amplified fragments that matched the predicted target bands.No 91 bp fragment was amplified from 18 germplasms of varied types,indicating a lack of Xa7 in them.Whereas Ry1,Ry2 and Ry3 had a 91 bp band,suggesting the inclusion of homozygous Xa7.Under an elevated temperature,Huazhan responded to the seven bacterial blight pathogens as highly susceptible(HS),intermediate susceptible(MS),or susceptible(S);R084 to six of the seven pathogens(HNA1-4,FuJ,GDA2,GD1358,PX086,and YN24)as highly resistant(HR),intermediate resistant(MR)or resistant(R);Ry-1 to five pathogens(GDA2,HNA1-4,FuJ,GD1358,and YN24)as HR or MR;Ry-2 to five pathogens(GDA2,GD1358,HNA1-4,PXO86,and YN24)as HR or R;and Ry-3 to 6 pathogens(HNA1-4,FuJ,GDA2,GD1358,PXO86,and YN24)as HR or MR.Therefore,the infiltration of Xa7 in the improved crossbred lines RY-1,RY-2,and RY-3 significantly accentuated the blight resistance of Huazhan.[Conclusions]Homozygous or hemizygous Xa7 could be accurately differentiated by the currently identified codominance functional marker Xa7 fun.The Xa7 introgression did not significantly alter the critical agronomic traits in the hybridization from generation to generation and could be safely applied in breeding rice varieties with bacterial blight resistance.
基金supported by the Ministry of Agriculture and Rural Affairs of China(2016ZX08009003-001)the National Natural Science Foundation of China(32071987,31871605)the Natural Science Foundation of Zhejiang Province(LD19C130001).
文摘Bacterial blight(BB)is a globally devastating rice disease caused by Xanthomonas oryzae pv.oryzae(Xoo).The use of disease resistance(R)genes in rice breeding is an effective and economical strategy for the control of this disease.Nevertheless,a majority of R genes lack durable resistance for long-term use under global warming conditions.Here,we report the isolation of a novel executor R gene,Xa7,that confers extremely durable,broad-spectrum,and heat-tolerant resistance to Xoo.The expression of Xa7 was induced by incompatible Xoo strains that secreted the transcription activator-like effector(TALE)AvrXa7 or PthXo3,which recognized effector binding elements(EBEs)in the Xa7 promoter.Furthermore,Xa7 induction was faster and stronger under high temperatures.Overexpression of Xa7 or co-transformation of Xa7 with avrXa7 triggered a hypersensitive response in plants.Constitutive expression of Xa7 activated a defense response in the absence of Xoo but inhibited the growth of transgenic rice plants.In addition,analysis of over 3000 rice varieties showed that the Xa7 locuswas found primarily in the indica and aus subgroups.A variation consisting of an 11-bp insertion and a base substitution(G to T)was found in EBEAvrXa7 in the tested varieties,resulting in a loss of Xa7 BB resistance.Through a decade of effort,we have identified an important BB resistance gene and characterized its distinctive interaction with Xoo strains;these findings will greatly facilitate research on the molecular mechanism of Xa7-mediated resistance and promote the use of this valuable gene in breeding.
基金supported by the United States Department of Agriculture National Institute of Agriculture and Food(2017-67013-26521 to B.Y.)the National Science Foundation(1238189 to F.F.W.,V.P.B.,and B.Y.,1741090 to F.F.W.)subawards to University of Missouri and University of Florida from the Heinrich Heine University Düsseldorf funded by the Bill&Melinda Gates Foundation[OPP1155704](B.Y.and F.F.W.).
文摘Many plant disease resistance(R)genes function specifically in reaction to the presence of cognate effectors from a pathogen.Xanthomonas oryzae pathovar oryzae(Xoo)uses transcription activator-like effectors(TALes)to target specific rice genes for expression,thereby promoting host susceptibility to bacterial blight.Here,we report the molecular characterization of Xa7,the cognate R gene to the TALes AvrXa7 and PthXo3,which target the rice major susceptibility gene SWEET14.Xa7 was mapped to a unique 74-kb region.Gene expression analysis of the region revealed a candidate gene that contained a putative AvrXa7 effector binding element(EBE)in its promoter and encoded a 113-amino-acid peptide of unknown function.Genome editing at the Xa7 locus rendered the plants susceptible to avrXa7-carrying Xoo strains.Both AvrXa7 and PthXo3 activated a GUS reporter gene fused with the EBE-containing Xa7 promoter in Nicotiana benthamiana.The EBE of Xa7 is a close mimic of the EBE of SWEET14 for TALe-induced disease susceptibility.Ectopic expression of Xa7 triggers cell death in N.benthamiana.Xa7 is prevalent in indica rice accessions from 3000 rice genomes.Xa7 appears to be an adaptation that protects against pathogen exploitation of SWEET14 and disease susceptibility.
