Studies on durable resistance of rice to blast in different latitudes

It has been an important problem on resistantbreeding that cultivar’s resistance of rice toblast disease caused by Magnaporthe grisea(Hebert)Barr.is easily broken down.In orderto find out resources with durable resistance toblast,the study was carried out during 1990--

QTL Mapping for Adult Plant Resistance to Powdery Mildew in Italian Wheat cv. Strampelli

The Italian wheat cv. Strampelli displays high resistance to powdery mildew caused by Blumeria graminis f. sp. tritici. The objective of this study was to map quantitative trait loci （QTLs） for resistance to powdery mildew in a population of 249 F2：3 lines from Strampelli/Huixianhong. Adult plant powdery mildew tests were conducted over 2 yr in Beijing and 1 yr in Anyang and simple sequence repeat （SSR） markers were used for genotyping. QTLs Qpm.caas-3BS, Qpm.eaas-5BL. 1, and Qpm.caas-7DS were consistent across environments whereas, Qpm.caas-2BS. 1 found in two environments, explained 0.4-1.6, 5.5-6.9, 27.1-34.5, and 1.0-3.5% of the phenotypic variation respectively. Qpm.caas-7DS corresponded to the genomic location of Pm38/Lr34/Yr18. Qpm.caas-4BL was identified in Anyang 2010 and Beijing 2011, accounting for 1.9-3.5% of phenotypic variation. Qpm.caas-2BS. 1 and Qpm.caas-5BL. 1 contributed by Strampelli and Qpm.caas-3BS by Huixianhong, seem to be new QTL for powdery mildew resistance. Qpm.caas-4BL, Qpm.caas-5BL.3, and Qpm.caas-7DS contributed by Strampelli appeared to be in the same genomic regions as those mapped previously for stripe rust resistance in the same population, indicating that these loci conferred resistance to both stripe rust and powdery mildew. Strampelli could be a valuable genetic resource for improving durable resistance to both powdery mildew and stripe rust in wheat.

Xa7, a new executor R gene that confers durable and broad-spectrum resistance to bacterial blight disease in rice

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.

Quantitative disease resistance:Multifaceted players in plant defense

In contrast to large-effect qualitative disease resistance,quantitative disease resistance(QDR)exhibits partial and generally durable resistance and has been extensively utilized in crop breeding.The molecular mechanisms underlying QDR remain largely unknown but considerable progress has been made in this area in recent years.In this review,we summarize the genes that have been associated with plant QDR and their biological functions.Many QDR genes belong to the canonical resistance gene categories with predicted functions in pathogen perception,signal transduction,phytohormone homeostasis,metabolite transport and biosynthesis,and epigenetic regulation.However,other"atypical"QDR genes are predicted to be involved in processes that are not commonly associated with disease resistance,such as vesicle trafficking,molecular chaperones,and others.This diversity of function for QDR genes contrasts with qualitative resistance,which is often based on the actions of nucleotidebinding leucine-rich repeat(NLR)resistance proteins.An understanding of the diversity of QDR mechanisms and of which mechanisms are effective against which classes of pathogens will enable the more effective deployment of QDR to produce more durably resistant,resilient crops.

Epigenetic regulation of paired NLR receptors confers durable disease resistance without yield penalty in rice

Subject Code:C14 With the support by the National Natural Science Foundation of China,the research team led by Prof.He Zuhua(何祖华)at the National Key Laboratory of Plant Molecular Genetics and National Center of Plant Gene Research,Shanghai Institute of Plant Physiology&Ecology,Chinese Academy of Sciences,

Ortholog Alleles at Xa3/Xa26 Locus Confer Conserved Race-Specific Resistance against Xanthomonas oryzae in Rice

The rice disease resistance （R） gene Xa3/Xa26 （having also been named Xa3 and Xa26） against Xanthomonas oryzae pv. oryzae （Xoo）, which causes bacterial blight disease, belongs to a multiple gene family clustered in chromosome 11 and is from an AA genome rice cultivar （Oryza sativa L.）. This family encodes leucine-rich repeat （LRR） receptor kinase- type proteins, Here, we show that the orthologs （alleles） of Xa3/Xa26, Xa3/Xa26-2, and Xa3/Xa26-3, from wild Oryza spe- cies O. officinalis （CC genome） and O. minuta （BBCC genome）, respectively, were also R genes against Xoo. Xa3/Xa26-2 and Xa3/Xa26-3 conferred resistance to 16 of the 18 Xoo strains examined. Comparative sequence analysis of the Xa3/Xa26 families in the two wild Oryza species showed that Xa3/Xa26-3 appeared to have originated from the CC genome of O. minuta. The predicted proteins encoded by Xa3/Xa26, Xa3/Xa26-2, and Xa3/Xa26-3 share 91-99% sequence identity and 94-99% sequence similarity. Transgenic plants carrying a single copy of Xa3/Xa26, Xa3/Xa26-2, or Xa3PXa26-3, in the same genetic background, showed a similar resistance spectrum to a set of Xoo strains, although plants carrying Xa3/Xa26-2 or Xa3/Xa26-3 showed lower resistance levels than the plants carrying Xa3/Xa26. These results suggest that the Xa3/Xa26 locus predates the speciation of A and C genome, which is approximately 7.5 million years ago. Thus, the resistance spec- ificity of this locus has been conserved for a long time.

Creation and judicious application of a wheat resistance gene atlas

Disease-resistance(R)gene cloning in wheat(Triticum aestivum)has been accelerated by the recent surge of genomic resources,facilitated by advances in sequencing technologies and bioinformatics.However,with the challenges of population growth and climate change,it is vital not only to clone and functionally characterize a few handfuls of R genes,but also to do so at a scale that would facilitate the breeding and deployment of crops that can recognize the wide range of pathogen effectors that threaten agroecosystems.Pathogen populations are continually changing,and breeders must have tools and resources available to rapidly respond to those changes if we are to safeguard our daily bread.To meet this challenge,we propose the creation of a wheat R-gene atlas by an international community of researchers and breeders.The atlas would consist of an online directory from which sources of resistance could be identified and deployed to achieve more durable resistance to the major wheat pathogens,such as wheat rusts,blotch diseases,powdery mildew,and wheat blast.We present a costed proposal detailing how the inter-acting molecular components governing disease resistance could be captured from both the host and the pathogen through biparental mapping,mutational genomics,and whole-genome association genetics.We explore options for the configuration and genotyping of diversity panels of hexaploid and tetraploid wheat,as well as their wild relatives and major pathogens,and discuss how the atlas could inform a dynamic,durable approach to R-gene deployment.Set against the current magnitude of wheat yield losses worldwide,recently estimated at 21%,this endeavor presents one route for bringing R genes from the lab to the field at a considerable speed and quantity.