Development of SNP, KASP, and SSR Markers by BSR-Seq Technology for Saturation of Genetic Linkage Map and Efficient Detection of Wheat Powdery Mildew Resistance Gene Pm61.

The gene Pm61 that confers powdery mildew resistance has been previously identified on chromosome arm 4AL in Chinese wheat landrace Xuxusanyuehuang (XXSYH). To facilitate the use of Pm61 in breeding practices, the bulked segregant analysis-RNA-Seq (BSR-Seq) analysis, in combination with the information on the Chinese Spring reference genome sequence, was performed in the F2:3 mapping population of XXSYH × Zhongzuo 9504. Two single nucleotide polymorphism (SNP), two Kompetitive Allele Specific PCR (KASP), and six simple sequence repeat (SSR) markers, together with previously identified polymorphic markers, saturated the genetic linkage map for Pm61, especially in the proximal side of the target gene that was short of gene-linked markers. In the newly established genetic linkage map, Pm61 was located in a 0.71 cM genetic interval and can be detected in a high throughput scale by the KASP markers Xicsk8 and Xicsk13 or by the standard PCR-based markers Xicscx497 and Xicsx538. The newly saturated genetic linkage map will be useful in molecular marker assisted-selection of Pm61 in breeding for disease resistant cultivar and in its map-based cloning.

Ribotypes of Polymyxa graminis in Wheat Samples Infected with Soilborne Wheat Viruses in China.

Polymyxa graminis is an obligate parasite and important vector of more than 14 soilborne plant viruses that pose a significant threat to cereal crops in Europe, North America, and Asia. Different ribotypes or formae speciales of P. graminis have been recognized and these may be associated with different cereal hosts or with transmission of different viruses. Two soilborne viruses infecting winter wheat in China have been reported and well studied (Wheat yellow mosaic virus [WYMV, genus Bymovirus] and Chinese wheat mosaic virus [CWMV, genus Furovirus]) but there has been no reported characterization of P. graminis isolates associated with them. In this study, the ribosomal DNA internal transcribed spacer (ITS) regions of P. graminis were examined from 63 wheat samples with apparent virus symptoms obtained from 16 sites within six Chinese provinces. Their associations with soilborne viruses were investigated. Ribotype I (P. graminis f. sp. temperata) and ribotype II (P. graminis f. sp. tepida) were confirmed in winter wheat regions of China for the first time. All 63 wheat root samples were infected with ribotype I of P. graminis and 11 were also infected with ribotype II. There was no obvious association between the ribotypes and infection by either WYMV or CWMV (or double infection). Phylogenetic analysis of the P. graminis ITS1-5.8S-ITS2 sequences revealed that ribotype I in China belongs to previously reported subgroup Ib, whereas ribotype II belongs to IIa. There was considerable sequence variation (pairwise distances from 0.0219 to 0.0319) between Chinese ribotype I isolates of different regions and previously reported ribotype I isolate Ken5 (accession number HE860055.1).

A furoviral replicase recruits host HSP70 to membranes for viral RNA replication.

Many host factors have been identified to be involved in viral infection. However, although furoviruses cause important diseases of cereals worldwide, no host factors have yet been identified that interact with furoviral genes or participate in the viral infection cycle. In this study, both TaHSP70 and NbHSP70 were up-regulated in Chinese wheat mosaic furovirus (CWMV)-infected plants. Their overexpression and inhibition were correlated with the accumulation of viral genomic RNAs, suggesting that the HSP70 genes could be necessary for CWMV infection. The subcellular distributions of TaHSP70 and NbHSP70 were significantly affected by CWMV infection or by infiltration of RNA1 alone. Further assays showed that the viral replicase encoded by CWMV RNA1 interacts with both TaHSP70 and NbHSP70 in vivo and vitro and that its region aa167-333 was responsible for the interaction. Subcellular assays showed that the viral replicase could recruit both TaHSP70 and NbHSP70 from the cytoplasm or nucleus to the granular aggregations or inclusion-like structures on the intracellular membrane system, suggesting that both HSP70s may be recruited into the viral replication complex (VRC) to promote furoviral replication. This is the first host factor identified to be involved in furoviral infection, which extends the list and functional scope of HSP70 chaperones.