Sharp eyespot is a major fungal disease of wheat caused by Rhizoctonia cerealis in cool and humid environments worldwide. In this study, 224 single seed descent derived F13, F14 and F15 recombinant inbred lines (RILs) from the cross between CI12633 (a resistant cultivar) and Yangmai 9 (a susceptible cultivar) were assessed for sharp eyespot resistance (R.cerealis isolate R0301) in field and greenhouse conditions in three growing seasons. Different agronomic characteristics were also evaluated in the field with no disease infection. All the lines were genotyped with the Illumina iSelect 90 K SNP wheat chip and 101 SSR markers. Sharp eyespot resistance was significantly negatively correlated with heading date and tiller angle, and significantly positively correlated with the diameter of the basal first internode and second internode. Five QTL with a likelihood of odds ratio score of higher than 3.0 were detected on chromosomes 2BS, 4BS, 5AL and 5BS, respectively. These identified QTL may be used in future wheat breeding programs through marker assisted selection for developing sharp eyespot resistant cultivars.

Red pericarp associates with seed dormancy or preharvest sprouting (PHS) tolerance in crops. To identify this association’s molecular mechanism, a PHS mutant Osviviparous1 (Osvp1) was characterized in rice and crossed with Kasalath, a red pericarp cultivar with Rc (red coleoptiles) genotype. Among the dehulled seeds of F2 progenies, RcRcvp1vp1 seeds performed a lower PHS rate than rcrcvp1vp1 seeds and showed shallower pigmentation than RcRcVP1VP1 seeds. Kasalath and SL9 (an RcRcVP1VP1 substitution line with Nipponbare background) showed more ABA sensitivity than the Nipponbare (rcrcVP1VP1) by the germination assay, and the transcriptional abundance of ABA signal genes OsABI2, OsSnRK2, OsVP1, ABI5, and especially OsVP1 increased in the red pericarp line SL9. Moreover, OsVP1 can directly bind Rc (bHLH) promoter by yeast one-hybrid, which activates Rc and OsLAR expression in red pericarp rice. Furthermore, a luciferase complementation imaging assay showed that OsVP1 interacts with transcriptions factors Rc and OsC1. These results indicate that OsVP1 promotes proanthocyanidin accumulation through the interaction among OsVP1, Rc, and OsC1 and then increases the plant’s ABA sensitivity and PHS resistance.

IntroductionWheat sharp eyespot caused by Rhizoctonia cerealis is a serious pathogenic disease affecting plants. The effective strategy for controlling this disease is breeding resistant cultivar. However, to date, no wheat varieties are fully resistant to sharp eyespot, and only a few quantitative trait loci (QTLs) have been shown to be associated with sharp eyespot resistance.MethodsTo understand the genetic basis of this disease, a genome-wide association study (GWAS) of sharp eyespot resistance in 262 varieties from all China wheat regions was conducted.ResultsAfter cultivation for three years, only 6.5% of the varieties were resistant to sharp eyespot. Notably, the varieties from the middle and lower Yangtze River displayed higher sharp eyespot resistance than those from Huanghuai wheat zone. Only two varieties had the same resistance level to the control Shanhongmai. The results of GWAS showed that 5 single nucleotide polymorphism (SNP) loci were markedly related to sharp eyespot resistance in the three years repeatedly, and two QTLs, qSE-6A and qSE-7B, on chromosome 6A and 7B were identified. Based on the ‘CG’ haplotypes of significant SNPs, we found that the two QTLs exhibited additive effects on attenuating sharp eyespot resistance.DiscussionThese results provide novel insights into the genetic basis of sharp eyespot resistance in China wheat varieties. The SNPs related to sharp eyespot resistance can be applied for marker-assisted selection in plant breeding.

Bread wheat (Triticum aestivum L.) is the most widely grown crop in the world. Rhizoctonia cerealis, the causal agent of wheat sharp eyespot disease, has 21 become epidemic in many countries. In the present study, we performed transcriptome analysis in wheat infected by R. cerealis at 0, 12, 30, 70, and 98 h post-infection using R. cerealis-resistant and -susceptible genotypes (CI12633 and ‘Yangmai15’, respectively). We used quantitative real-time PCR to validate the Illumina gene expression data, and identified new gene annotations for 23,654 unigenes in the RNA samples from the resistant and susceptible cultivars. Comparing the same inoculation times, we found that the number of DEGs (differentially-expressed genes) increased gradually before 70 h and declined at 98 h in the two RNA samples. Furthermore, the expression of resistance-associated genes occurred earlier in CI12633 than in ‘Yangmai15’, and higher mRNA expression levels were detected in CI12633; this suggests that timing and relative expression levels of these genes are important in the CI12633-R. cerealis interaction. Functional annotations associated with sharp eyespot resistance included genes involved in energy production and conversion, posttranslational modification, protein turnover, chaperones, secondary metabolite biosynthesis, transport and catabolism, and defense mechanisms. The results of pathway enrichment analysis showed that the DEGs participate in glutathione metabolism, glycerophospholipid metabolism, lysine degradation, plant-pathogen interaction, glyoxylate and dicarboxylate metabolism, and other resistance-associated metabolic pathways. Disease inoculation experiments and the validation of in vitro antifungal activity of the candidate genes showed that the genes were up- or down-regulated in the resistant genotype CI12633 30 h after inoculation compared to its control, which validated the results of the RNA-seq analysis. The results of our study will help to understand the molecular basis of the host response to R. cerealis infection in wheat, and will also enable the future genetic improvement of sharp eyespot resistance in wheat through the incorporation of novel resistance genes.