Molecular cytogenetic characterization of a new wheat-rye 1BL•1RS translocation line expressing superior stripe rust resistance and enhanced grain yield

Main conclusion

A new wheat-rye 1BL?1RS translocation line, with the characteristics of superior stripe rust resistance and high thousand-kernel weight and grain number per spike, was developed and identified from progenies of wheat-rye- Psathyrostachys huashanica trigeneric hybrids.

Abstract

The wheat-rye 1BL?1RS translocation line from Petkus rye has contributed substantially to the world wheat production. However, due to extensive growing of cultivars with disease resistance genes from short arm of rye chromosome 1R and coevolution of pathogen virulence and host resistance, these cultivars successively lost resistance to pathogens. In this study, a new wheat-rye line K13-868, derived from the progenies of wheat-rye-Psathyrostachys huashanica trigeneric hybrids, was identified and analyzed using fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH), acid polyacrylamide gel electrophoresis (A-PAGE), and molecular markers. Cytological studies indicated that the mean chromosome configuration of K13-868 at meiosis was 2n = 42 = 0.14 I + 18.78 II (ring) + 2.15 II (rod). Sequential FISH and GISH results demonstrated that K13-868 was a compensating wheat-rye 1BL?1RS Robertsonian translocation line. Acid PAGE analysis revealed that clear specific bands of rye 1RS were expressed in K13-868. Simple sequence repeat (SSR) and rye 1RS-specific markers ω-sec-p1/ω-sec-p2 and O-SEC5′-A/O-SEC3′-R suggested that the 1BS arm of wheat had been substituted by the 1RS arm of rye. At the seedling and adult growth stage, compared with its recurrent wheat parent SM51 and six other wheat cultivars containing the 1RS arm in southwestern China, K13-868 showed high levels of resistance to stripe rust (Puccinia striiformis f. sp. tritici, Pst) pathogens prevalent in China, which are virulent to Yr10 and Yr24/Yr26. In addition, K13-868 expresses higher thousand-kernel weight and more grain number per spike than these controls in two growing seasons, suggesting that this line may carry yield-related genes of rye. This translocation line, with significant characteristics of resistance to stripe rust and high thousand-kernel weight and grain number per spike, could be utilized as a valuable germplasm for wheat improvement.

     

Introgression of chromosome 3Ns from Psathyrostachys huashanica into wheat specifying resistance to stripe rust

Wheat stripe rust is a destructive disease in the cool and humid wheat-growing areas of the world. Finding diverse sources of stripe rust resistance is critical for increasing genetic diversity of resistance for wheat breeding programs. Stripe rust resistance was identified in the alien species Psathyrostachys huashanica, and a wheat-P. huashanica amphiploid line (PHW-SA) with stripe rust resistance was reported previously. In this study, a P. huashanica 3Ns monosomic addition line (PW11) with superior resistance to stripe rust was developed, which was derived from the cross between PHW-SA and wheat J-11. We evaluated the alien introgressions PW11-2, PW11-5 and PW11-8 which were derived from line PW11 for reaction to new Pst race CYR32, and used molecular and cytogenetic tools to characterize these lines. The introgressions were remarkably resistant to CYR32, suggesting that the resistance to stripe rust of the introgressions thus was controlled by gene(s) located on P. huashanica chromosome 3Ns. All derived lines were cytologically stable in term of meiotic chromosome behavior. Two 3Ns chromosomes of P. huashanica were detected in the disomic addition line PW11-2. Chromosomes 1B of substitution line PW11-5 had been replaced by a pair of P. huashanica 3Ns chromosomes. In PW11-8, a small terminal segment from P. huashanica chromosome arm 3NsS was translocated to the terminal region of wheat chromosomes 3BL. Thus, this translocated chromosome is designated T3BL-3NsS. These conclusions were further confirmed by SSR analyses. Two 3Ns-specific markers Xgwm181 and Xgwm161 will be useful to rapidly identify and trace the translocated fragments. These introgressions, which had significant characteristics of resistance to stripe rust, could be utilized as novel germplasms for wheat breeding.     

偃麦草属植物醇溶蛋白和谷蛋白多态性及系统学研究

运用酸性聚丙烯酰胺凝胶电泳(A-PAGE)和十二烷基硫酸钠聚丙烯酰胺凝胶电泳(SDS-PAGE)对偃麦草属(Elytrigia)24个物种的醇溶蛋白和谷蛋白进行了研究。以中国春为参照,按醇溶蛋白和谷蛋白电泳图谱条带迁移距离大小和条带多态性对供试材料进行聚类分析。结果显示,24份供试材料均呈现不同的醇溶蛋白和谷蛋白电泳图谱,共分离出醇溶蛋白带纹83条和谷蛋白带纹53条,多态性均达100%,并且在相同染色体组组成的物种中,染色体数目越多,其蛋白带纹越多;偃麦草属24个物种的醇溶蛋白和谷蛋白图谱均有明显差异,蛋白图谱可作为鉴定偃麦草属物种的指纹图谱。聚类分析结果显示,在材料间的醇溶蛋白遗传相似性系数为0.66时,24份材料被划分为6个主要类群,含E和St基因组的物种具有较近的亲缘关系;在谷蛋白遗传相似性系数为0.62时,24份材料被聚为4大类。聚类结果表明,染色体组成未知的物种Et.pachynera可能为异源多倍体物种。     

Development and characterization of wheat-Psathyrostachys huashanica partial amphiploids for resistance to stripe rust

Two partial amphiploid lines, B113 (32 plants) and B21 (13 plants), derived from a wheat-Psathyrostachys huashanica intergeneric cross were characterized by Giemsa C-banding and SDS-PAGE and evaluated for stripe rust resistance. All 15 partial amphiploid plants were aneuploids with either 50 (8 plants), 51 (6 plants) or 54 (1 plant) chromosomes. Some showed regular meiosis and all the P. huashanica chromosomes were included, although not in a single plant. Of 45 plants 34 showed specific bands on SDS-PAGE representing high molecular weight glutenin subunit (HMW-GS) and 41 had bands representing P. huashanica low molecular weight glutenin subunit (LMW-GS), including two new subunits. All 45 plants were highly resistant (10) or immune (35) to stripe rust mixed races CYR-30, CYR-31, Shuiyuan 7 and Shuiyuan 14. These amphiploid plants could be useful germplasm for enhancing stripe rust resistance and might improve wheat grain quality.     

Phylogenetic relationships between Hystrix and its closely related genera (Triticeae; Poaceae) based on nuclear Acc1, DMC1 and chloroplast trnL-F sequences

To estimate the phylogenetic relationship of polyploid Hystrix in Triticeae, two single-copy nuclear genes (Acc1 and DMC1) and chloroplast trnL-F sequences of six Hystrix taxa were analyzed with those of nine Leymus species (NsXm), four Elymus species (StH) and 13 diploid taxa from seven monogenomic genera. Phylogenetic analyses reveal that Hystrix taxa contain two distinct types of genome constitution, despite the overall morphological and ecological similarity among Hystrix taxa. One type of genome constitution is StH (Hy. patula) as Elymus, the other is NsXm (Hy. californica, Hy. coreana, Hy. duthiei, Hy. duthiei ssp. longearistata and Hy. komarovii) as Leymus. The St, H and Ns genomes in Hystrix are donated by Pseudoroegneria, Hordeum and Psathyrostachys, respectively. The donor of the Xm genome is closely related to Agropyron (P). The trnL-F data especially indicate that there has been a maternal haplotype polymorphism in Hystrix species. Based on these results, we suggest that Hy. coreana, Hy. duthiei, Hy. duthiei ssp. longearistata, Hy. komarovii and Hy. californica should be included in the genus Leymus, and Hy. patula in the genus Elymus.     

A hexaploid triticale 4D (4B) substitution line confers superior stripe rust resistance

Triticale lines tend to become less resistant to stripe rust and other fungal diseases over time and exhibit relatively limited genetic diversity. Therefore, it is important that new triticale varieties with superior agronomic traits are continually produced to enrich the available genetic pool. In this study, a new hexaploid triticale line (K14-827-1), which was derived from the progenies of a wheat–rye–Psathyrostachys huashanica trigeneric hybrid, was identified and analyzed using genomic and fluorescence in situ hybridizations, seed protein profiling, and molecular markers. Meiotic pairing studies suggested that the mean chromosomal configuration of K14-827-1 was 2n = 42 = 0.24 I + 18.23 II (ring) + 2.65 II (rod). The in situ hybridization karyotyping results indicated that K14-827-1 was a 4D (4B) substitution line, consisting of complete R and A genomes and chromosomes 4D, 1B–3B, and 5B–7B. Simple sequence repeat analysis of K14-827-1 confirmed that wheat chromosome 4B had been substituted by chromosome 4D. The seed protein profiling results uncovered polymorphic 75K γ-secalin and low-molecular-weight glutenin subunits between K14 - 827-1 and its recurrent triticale parent (Zhongsi828). Furthermore, the K14-827-1 plants were highly resistant to the stripe rust pathogen (Puccinia striiformis f. sp. tritici) prevalent in China, including race V26/Gui22, than Zhongsi828 plants at the seedling and adult stages. This new hexaploid triticale line may be useful for diversifying triticale germplasms and breeding new varieties with improved forage grass traits.     

Morphological,cytological, and molecular evidences for natural hybridization between Roegneria stricta and Roegneria turczaninovii (Triticeae: Poaceae)

Some plants with low fertility are morphologically intermediate between Roegneria stricta and Roegneria turczaninovii, and were suspected to be natural hybrids between these species. In this study, karyotype analysis showed that natural hybrids and their putative parents were tetraploids (2n = 4x = 28). Meiotic pairing in natural hybrids is more irregular than its putative parents. Results of genomic in situ hybridization and fluorescence in situ hybridization indicate that natural hybrids contain the same genome as their putative parents. The nuclear gene DNA meiotic recombinase 1 (DMC1) and the chloroplast gene rps16 of natural hybrids and their putative parents were analyzed for evidence of hybridization. The results from molecular data supported by morphology and cytology demonstrated that the plants represent natural hybrids between R. stricta and R. turczaninovii. The study is important for understanding species evolution in the genus since it demonstrates for the first time the existence of populations of natural homoploid hybrids in Roegneria. The study also reports for the first time that the composition of the genomic formula of R. turczaninovii is StY, confirming that the current taxonomic status is correct.     

Density functional theory for the selective adsorption of small molecules on a surface modified with polymer brushes

A density functional method based on weighted density approximation is extended to study the selective adsorption of small molecules on a surface modified with end-grafted square-well chains. The excess part of the Helmholtz free energy functional is divided into two components: the hard sphere repulsion and the square-well attraction. The equation of state for hard sphere chain fluids developed by Liu et al. is used to calculate the repulsive part of the excess Helmholtz free energy functional, and the equation of state for square-well chain fluid with variable range developed by Li et al. is employed to calculate the attractive part. With this theoretical model, we examine the physical properties of the grafted polymer and the selective adsorption of small molecules on the modified surface.     

Differential Responses of Two Wheat Varieties Differing in Salt Tolerance to the Combined Stress of Mn and Salinity

The effect of Mn and NaCl on growth, mineral nutrients and antioxidative enzymes in two tetroploid wheat genotypes differing in salt tolerance was investigated in this study. 100 mM NaCl and Mn stress significantly inhibited plant growth, photosynthesis and Ca uptake, while stimulated ROS accumulation, MDA and proline content in wheat plants, Mn stress also increased SOD, APX, GR and DHAR activities. Durum wheat (AS780) was less affected by 100 mM NaCl and Mn stress than emmer wheat (AS847) due to more proline production, higher antioxidative enzymes activities and less-affected mineral nutrients. Application of 10 mM NaCl to Mn-stressed durum wheat alleviated Mn-induced damage by reducing Mn accumulation and translocation, while promoting proline accumulation and SOD, APX and GR activities. Irrespective of NaCl level, the combined stress of Mn and NaCl caused more severe oxidative stress, result in further reduction of photosynthetic rate and plant growth in emmer wheat as compared to Mn stress alone. The additively negative effects of NaCl and Mn stress on growth of emmer wheat results from reduced SOD and APX activities as well as Ca, Cu and Fe accumulation in both shoots and roots. These results suggest that salt-tolerant durum wheat is superior to emmer in adapting to Mn stress and the combined stress of salinity and Mn.

     

Molecular phylogeny and maternal progenitor implication in the genus Kengyilia (Triticeae: Poaceae): Evidence from COXII intron sequences

Kengyilia is a perennial genus distributing in central and western Asia. Here, the levels of nucleotide diversity for COXII intron were obtained. The estimates of nucleotide diversity for different genome constitution ranged from θ = 0.00082 and π = 0.00082 for St genome species to π = 0.01227 and θ = 0.01229 for P genome species. Employing COXII intron sequences, the phylogenetic relationships within Kengyilia and between Kengyilia genus and its closely related genera were examined. The Maximum Parsimony analysis demonstrated that Kengyilia species were positioned into two clades corresponding to different maternal genomic donor. Kengyilia stenachyra, Kengyilia grandiglumis, Kengyilia hirsuta, Kengyilia melanthera, Kengyilia thoroldiana, Kengyilia alatavica and Kengyilia zhaosuensis were related to species of Agropyron, while Kengyilia kokonorica, Kengyilia rigidula, Kengyilia nana, Kengyilia mutica, Kengyilia longiglumis, Kengyilia laxiflora and Kengyilia gobicola were close to species of Roegneria and Pseudoroegneria. In addition, other three species of Kengyilia, such as Kengyilia batalinii, Kengyilia tahelacana and Kengyilia kaschgarica, were related to Douglasdeweya deweyi, Pseudoroegneria strigosa and Roegneria tibetica. This result indicated that there had been two phylogenetically divergent maternal donors within Kengyilia. Our new finding will help to understand the evolutionary history of the genus Kengyilia.