Map-based Cloning Of Fhb1,a Major QTL Confers Fusarium Head Blight Resistance In Wheat Landrace Wangshuibai(Triticum Aestivum L.)

Fusarium head blight(FHB),a fungal disease caused by Fusarium graminearum species complex,is a disastrous disease of wheat and barley,which not only reduces the grain yield,but also contains deoxynivalenol and other toxins,which seriously affect the health of human and livestock.Among the measures adopted to curb this disease,deployment of scab-resistant varieties is the most preferred strategy for its economy and environmental friendliness.Due to scarcity of resistant germplasm in wheat and lack of understanding of resistance mechanisms has greatly hindered the breeding efforts.Wangshuibai is one of the best indigenous scab resistance germplasms in Liyang,Jiangsu,China.In previously study,Qfhs.nau-3B,a major QTL derived from Wangshuibai.The purpose of the study is map-based cloning of Qfhs.nau-3B from a Chinese wheat cultivar Wangshuibai.Near isogenic lines of the Qfhs.nau-3B,developed using FHB-susceptible line PH691,was used in NIL-derived secondary F2 population construction.Using recombinants identified in population,Qfhs.nau-3B was fine mapped.We generated additional markers from the BAC clones.Qfhs.nau-3B was confined to a interval Xmag8937-Xmag9404.The 23.8-kb physical interval containing two genes by bioinformatics predicted.To compare Qfhs.nau-3B with Fhb1 in Sumai3,we also fine mapped the Fhb1 using similar approach.Fhb1 was confined to a 26.8-kb physical interval Xmag8937-Xmag9452.We found that Wangshuibai and Sumai3 possess the same FHB resistance gene in the Fhb1 interval.Based on polymorphic sequence in Fhb1 interval between resistant and susceptible cultivars revealed the candidate gene:Histidine-rich calcium-binding protein,His.For Fhb1(HisR),comparing PH691 His-3B(HisS),752 bp deletion within 5' end of His ORF result in N-terminal amino acid change.Full-length cDNA isolation revealed different types transcript variants for His.Expression analysis of His showed a constitutive expression in various organs,including root,culm,leaf and spike.An associated mapping and haplotype analysis indicated that HisR 752-bp deletion is key mutation in defining the different FHB resistance in the 151 wheat accessions.Importantly,transgenic plant expressing HisR from native promoter showed more resistance to F.graminearum than non-transgenic plants.For RNAi-induce gene silence,the expression of HisR to be significantly reduce abundance in NIL R-43 with His-RNAi contructs plants compared to R-43 and negative transgenic line,its became susceptible compare with R-43 and the corresponding negative-transgene segregants.The transgenic plants with successful gene silencing of Hiss,all of them show maintained FHB susceptibility similar with PH691.We conclude that the 5' 752 bp deletion in HisR might be a gain of function mutation for FHB resistance in wheat.The His genes are present in 243 Triticum species,including einkorn.emer,Timopheevii,Zhukovskyi,T.taushii and hexaploid wheat based on His specific markers detection.Two to four haplotypes were found in each of the three sub-genomes based on His induced protein sequences alignment in 51 wheat accessions and their coding products have at least 92%amino acid identity.The WSB/S3 type polypeptide variation caused by the 752-bp deletion was solely found in sub-genome B of common wheat and show that HisR is a unique mutation in wheat.Extending the conservation analysis to other monocot and dicot plants,we found that plant His homologous sequences were highly conserved in the N-terminus sequence and C-terminus amino acid composition of these proteins.The highly conserved of His coding products among species implies that the His products are essential to plants.To find out the geographical distribution of wheat germplasm carrying HisR,643 worldwide wheat collections were surveyed with marker Xwgrb619.Most of wheat cultivars carrying HisR originated in China.More than 70%of wheat cultivars with HisR originated in the lower reaches of the Yangtze River Valley.We found more than half of the landraces surveyed and originated in the lower reaches of the Yangtze River Valley carried HisR.In order to explore the origin of Fhb1,genetic similarity analysis in 643 common wheat varieties on the basis of nine markers within the 131.6 kb interval surrounding the Fhb1 and cluster analysis in 467 wheat varieties using 90k SNP chip data.These results suggest that Fhb1 originates in the lower reaches of the Yangtze River Valley.