RNA-seq bulked segregant analysis combined with KASP genotyping rapidly identified PmCH7087 as responsible for powdery mildew resistance in wheat

Application of bulk segregant RNA-Seq (BSR-Seq) and allele-specific primers to study soybean powdery mildew resistance

BACKGROUND

Powdery mildew (PM) is one of the important soybean diseases, and host resistance could practically contribute to soybean PM management. To date, only the Rmd locus on chromosome (Chr) 16 was identified through traditional QTL mapping and GWAS, and it remains unclear if the bulk segregant RNA-Seq (BSR-Seq) methodology is feasible to explore additional PM resistance that might exist in other varieties.

RESULTS

BSR-Seq was applied to contrast genotypes and gene expressions between the resistant bulk (R bulk) and the susceptible bulk (S bulk), as well as the parents. The ∆(SNP-index) and G' value identified several QTL and significant SNPs/Indels on Chr06, Chr15, and Chr16. Differentially expressed genes (DEGs) located within these QTL were identified using HISAT2 and Kallisto, and allele-specific primers (AS-primers) were designed to validate the accuracy of phenotypic prediction. While the AS-primers on Chr06 or Chr15 cannot distinguish the resistant and susceptible phenotypes, AS-primers on Chr16 exhibited 82% accuracy prediction with an additive effect, similar to the SSR marker Satt431.

CONCLUSIONS

Evaluation of additional AS-primers in the linkage disequilibrium (LD) block on Chr16 further confirmed the resistant locus, derived from the resistant parental variety 'Kaohsiung 11' ('KS11'), not only overlaps with the Rmd locus with unique up-regulated LRR genes (Glyma.16G213700 and Glyma.16G215100), but also harbors a down-regulated MLO gene (Glyma.16G145600). Accordingly, this study exemplified the feasibility of BSR-Seq in studying biotrophic disease resistance in soybean, and showed the genetic makeup of soybean variety 'KS11' comprising the Rmd locus and one MLO gene.

Using association mapping and local interval haplotype association analysis to improve the cotton drought stress response

Drought stress has a serious impact on the growth and development of cotton. To explore the relevant molecular mechanism of the drought stress response in cotton, gene mapping based on the QTL interval mapped by simplified genome BSA-seq of the drought-resistance-related RIL population was performed. A QTL region spanning 2.02 Mb on chromosome D07 was selected, and 201 resource materials were genotyped using 9 KASP markers in the interval. After local interval haplotype association analysis, the overlap of the 110 kb peak region confirmed the reliability of this region, and at the same time, the role of GhGF14-30, the only gene in the overlapping region, was modeled in the response of cotton to drought stress. qRTPCR analysis of the materials and population parents proved that this gene plays a role in the drought stress response in cotton. Virus-induced gene silencing proved the importance of this gene in drought-sensitive materials, and drought-resistance-related marker genes also proved that the GhGF14-30 gene may play an important role in the ABA and SOS signaling pathways. This study provides a basis for mining drought stress response functional genes in cotton and lays the foundation for the molecular mechanism of the GhGF14-30 gene in response to drought stress in cotton.

The Detection of Yr Genes in Xinjiang Wheat Cultivars Using Different Molecular Markers

Wheat stripe rust is a fungal disease caused by Puccinia striiformis f. sp. Tritici (Pst). It significantly impacts wheat yields in Xinjiang, China. Breeding and promoting disease-resistant cultivars carrying disease-resistance genes remains the most cost-effective strategy with which to control the disease. In this study, 17 molecular markers were used to identify Yr5, Yr9, Yr10, Yr15, Yr17, Yr18, Yr26, Yr41, Yr44, and Yr50 in 82 wheat cultivars from Xinjiang. According to the differences in SNP loci, the KASP markers for Yr30, Yr52, Yr78, Yr80, and Yr81 were designed and detected in the same set of 82 wheat cultivars. The results showed that there was a diverse distribution of Yr genes across all wheat cultivars in Xinjiang, and the detection rates of Yr5, Yr15, Yr17, Yr26, Yr41, and Yr50 were the highest, ranging from 74.39% to 98.78%. In addition, Yr5 and Yr15 were prevalent in spring wheat cultivars, with detection rates of 100% and 97.56%, respectively. A substantial 85.37% of wheat cultivars carried at least six or more different combinations of Yr genes. The cultivar Xindong No.15 exhibited the remarkable presence of 11 targeted Yr genes. The pedigree analysis results showed that 33.33% of Xinjiang wheat cultivars shared similar parentage, potentially leading to a loss of resistance against Pst. The results clarified the Yr gene distribution of the Xinjiang wheat cultivars and screened out varieties with a high resistance against Pst.

The putative vacuolar processing enzyme gene TaVPE3cB is a candidate gene for wheat stem pith-thickness

KEY MESSAGE

The vacuolar processing enzyme gene TaVPE3cB is identified as a candidate gene for a QTL of wheat pith-thickness on chromosome 3B by BSR-seq and differential expression analyses. The high pith-thickness (PT) of the wheat stem could greatly enhance stem mechanical strength, especially the basal internodes which support the heavier upper part, such as upper stems, leaves and spikes. A QTL for PT in wheat was previously discovered on 3BL in a double haploid population of 'Westonia' × 'Kauz'. Here, a bulked segregant RNA-seq analysis was applied to identify candidate genes and develop associated SNP markers for PT. In this study, we aimed at screening differentially expressed genes (DEGs) and SNPs in the 3BL QTL interval. Sixteen DEGs were obtained based on BSR-seq and differential expression analyses. Twenty-four high-probability SNPs in eight genes were identified by comparing the allelic polymorphism in mRNA sequences between the high PT and low PT samples. Among them, six genes were confirmed to be associated with PT by qRT-PCR and sequencing. A putative vacuolar processing enzyme gene TaVPE3cB was screened out as a potential PT candidate gene in Australian wheat 'Westonia'. A robust SNP marker associated with TaVPE3cB was developed, which can assist in the introgression of TaVPE3cB.b in wheat breeding programs. In addition, we also discussed the function of other DEGs which may be related to pith development and programmed cell death (PCD). A five-level hierarchical regulation mechanism of stem pith PCD in wheat was proposed.