Evaluation and identification of powdery mildew resistance genes in Aegilops tauschii Coss and emmer wheat accessions

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a serious threat to wheat (Triticum aestivum L.) production. Narrow genetic basis of common wheat boosted the demand for diversified donors against powdery mildew. Aegilops tauschii Coss (2n = 2x = DD) and emmer wheat (2n = 4x = AABB), as the ancestor species of common wheat, are important gene donors for genetic improvement of common wheat. In this study, a total of 71 Ae. tauschii Coss and 161 emmer wheat accessions were firstly evaluated their powdery mildew resistance using the Bgt isolate E09. Thirty-three Ae. tauschii Coss (46.5%) and 108 emmer wheat accessions (67.1%) were resistant. Then, all these accessions were tested by the diagnostic markers for 21 known Pm genes. The results showed that Pm2 alleles were detected in all the 71 Ae. tauschii Coss and only Pm4 alleles were detected in the 20 of 161 emmer wheat accessions. After haplotype analysis, we identified four Pm4 alleles (Pm4a, Pm4b, Pm4d and Pm4f) in the emmer wheat accessions and three Pm2 alleles (Pm2d, Pm2e and Pm2g) in the Ae. tauschii Coss. Further resistant spectrum analysis indicated that these resistance accessions displayed different resistance reactions to different Bgt isolates, implying they may have other Pm genes apart from Pm2 and/or Pm4 alleles. Notably, a new Pm2 allele Pm2S was identified in the Ae. tauschii Coss, which contained a 64 bp deletion in the first exon and formed a new termination site at the 513th triplet of the shifted reading frame compared to reported Pm2 alleles. The phylogenetic tree of Pm2S showed that the kinship of Pm2S was closed to Pm2h. To efficiently and accurately detect Pm2S and distinguish with other Pm2 alleles in Ae. tauschii Coss background, a diagnostic marker YTU-QS-3 was developed and verified its effectiveness. This study provided valuable Pm alleles and enriched the genetic diversity of the powdery mildew resistance in wheat improvement.

Investigating the dynamic responses of Aegilops tauschii Coss. to salinity, drought, and nitrogen stress: a comprehensive study of competitive growth and biochemical and molecular pathways

Aegilops tauschii (Coss.) is a highly deleterious, rapidly proliferating weed within the wheat, and its DD genome composition exhibits adaptability toward diverse abiotic stresses and demonstrates heightened efficacy in nutrient utilization. Current study investigated different variegated impacts of distinct nitrogen concentrations with varied plant densities, scrutinizing the behavior of Ae. tauschii under various salinity and drought stress levels through multiple physiological, biochemical, and molecular pathways. Different physiological parameters attaining high growth with different plant density and different nitrogen availability levels increased Ae. tauschii dominancy. Conversely, under the duress of salinity and drought, Ae. tauschii showcased an enhanced performance through a comprehensive array of physiological and biochemical parameters, including catalase, peroxidase, malondialdehyde, and proline content. Notably, salinity-associated traits such as sodium, potassium, and the sodium-potassium ratio exhibited significant variations and demonstrated remarkable tolerance capabilities. In the domain of molecular pathways, the HKT and DREB genes have displayed a remarkable upregulation, showcasing a comparatively elevated expression profile in reaction to different levels of salinity and drought-induced stress. Without a doubt, this information will make a substantial contribution to the understanding of the fundamental behavioral tendencies and the efficiency of nutrient utilization in Ae. tauschii. Moreover, it will offer innovative viewpoints for integrated management, thereby enabling the enhancement of strategies for adept control and alleviation.

Selection and Validation of Reference Genes for RT-qPCR Analysis in Aegilops tauschii (Coss.) under Different Abiotic Stresses

Aegilops tauschii (Coss.) is an aggressive and serious annual grass weed in China. Its DD genome is a rich source of genetic material and performs better under different abiotic stress conditions (salinity, drought, temperature, etc.). Reverse-transcribed quantitative polymerase chain reaction (RT-qPCR) is a reliable technique for reference gene selection and validation. This work aimed to evaluate the stability of reference gene expression in Ae. tauschii under different abiotic stresses (salinity, drought, hot, and cold) and developmental stages (seedling and development). The results show that the ubiquitin-conjugating enzyme E2 36-like (UBC36) and protein microrchidia 2-like (HSP) are the most stable genes under control and salinity conditions, respectively. Under drought stress conditions, UBC36 is more stable as compared with others. Glyceraldehyde-3-phosphate dehydrogenase (GADPH) is the most stable reference gene during heat stress conditions and thioredoxin-like protein (YLS) under cold stress condition. Phosphate2A serine/threonine-protein phosphatase 2A (PP2A) and eukaryotic translation initiation factor 3 (ETIF3) are the most stable genes at seedling and developmental stages. Intracellular transport protein (CAC) is recommended as the most stable gene under different abiotic stresses and at developmental stages. Furthermore, the relative expression levels of NHX1 and DREB under different levels of salinity and drought stress conditions varied with the most (HSP and UBC36) and least (YLS and ACT) stable genes. This study provides reliable reference genes for understanding the tolerance mechanisms in Ae. tauschii under different abiotic stress conditions.

Genetic Diversity and Synergistic Modulation of Salinity Tolerance Genes in Aegilops tauschii Coss

Aegilops tauschii Coss. (2n = 2x = 14, DD) is a problematic weed and a rich source of genetic material for wheat crop improvement programs. We used physiological traits (plant height, dry weight biomass, Na⁺ and K⁺ concentration) and 14 microsatellite markers to evaluate the genetic diversity and salinity tolerance in 40 Ae. tauschii populations. The molecular marker allied with salinity stress showed polymorphisms, and a cluster analysis divided the populations into different groups, which indicated diversity among populations. Results showed that the expression level of AeHKT1;4 and AeNHX1 were significantly induced during salinity stress treatments (50 and 200 mM), while AeHKT1;4 showed relative expression in roots, and AeNHX1 was expressed in leaves under the control conditions. Compared with the control conditions, the expression level of AeHKT1;4 significantly increased 1.7-fold under 50 mM salinity stress and 4.7-fold under 200 mM salinity stress in the roots of Ae. tauschii. AeNHX1 showed a relative expression level of 1.6-fold under 50 mM salinity stress and 4.6-fold under 200 mM salinity stress compared with the control conditions. The results provide strong evidence that, under salinity stress conditions, AeHKT1;4 and AeNHX1 synergistically regulate the Na⁺ homeostasis through regulating Na⁺ transport in Ae. tauschii. AeNHX1 sequestrated the Na⁺ into vacuoles, which control the regulation of Na⁺ transport from roots to leaves under salinity stress conditions in Ae. tauschii.

and its phytohormonal regulation

Aegilops tauschii Coss, a notorious wheat field weed, poses a serious threat to wheat in China. Tillers are an important agronomic tool for yield. In this study, a total of 12 Ae. tauschii populations were collected from China to investigate the effect of plant density on tiller occurrence and its phytohormonal regulation. We assayed the growth parameters of Ae. tauschii and the levels of endogenous hormones at different plant densities. The results showed that plant density had a significant effect on the quantity and quality of Ae. tauschii seeds produced per plant. In particular, the tiller and spike numbers per plant were negatively affected by plant density (P < 0.0001). The contents of 13 endogenous hormones in the tiller nodes changed in response to plant density. Among them, indole-3-acetic acid (IAA) and gibberellin (GA) positively responded to plant density. However, the reverse result was found for cytokinin (CTK). Interestingly, phylogenetic tree analysis of auxin (AeYUCCA), CK (AeIPT) and GA (AeCPS) biosynthesis related genes found that phylogenies in the Gramineae for the three different genes were various, hinting at horizontal gene transfer. Moreover, the dynamics of the expression of AeYUCCA, AeIPT and AeCPS were roughly consistent with their phytohormone contents during tillering stage. When externally sprayed on plants of Ae. tauschii, 2,4-D isooctyl ester and GA₃ markedly reduced its tillering while 6-BA had no significant effect.

from the VIR collection

Broadening of the genetic diversity of donors of resistance to biotic environmental factors is a challenging problem concerning Triticum L., which can be solved by using wild relatives of wheat, in particular, Aegilops tauschii Coss., in breeding programs. This species, believed to be the donor of D genome of common wheat (T. aestivum L.), is a source of some traits important for breeding. This greatly facilitates the possibility of crossing Ae. tauschii with common wheat. Aegilops L. species are donors of effective genes for resistance to fungal diseases in wheat. For instance, genes that determine resistance to rust agents in common wheat were successfully introgressed from Ae. tauschii into the genome of T. aestivum L. The aim of our study was to identify differences in metabolomic profiles of Ae. tauschii forms (genotypes), resistant or susceptible to such fungal pathogens as Puccinia triticina f. sp. tritici and Erysiphe graminis f. sp. tritici. These indicators may be used as biochemical markers of resistance. A comparative analysis of groups of Ae. tauschii accessions showed that metabolomic profiles of the forms with or without resistance to fungal pathogens differed significantly in the contents of nonproteinogenic amino acids, polyols, phytosterols, acylglycerols, mono- and oligosaccharides, glycosides, phenolic compounds (hydroquinone, kempferol), etc. This fact was consistent with the previously obtained data on the relationship between Fusarium resistance in oats (Avena sativa L.) and certain components of the metabolomic profile, such as acylglycerols, nonproteinogenic amino acids, galactinol, etc. Thus, our studies once again confirmed the possibility and effectiveness of the use of metabolomic analysis for screening the genetic diversity of accessions in the VIR collection, of Ae. tauschii in particular, in order to identify forms with a set of compounds in their metabolomic profile, which characterize them as resistant. Ae. tauschii accessions with a high content of pipecolic acids, acylglycerols, galactinol, stigmasterol, glycerol, azelaic and pyrogallic acids, campesterol, hydroquinone, etc., can be used for creating wheat and triticale cultivars with high resistance to fungal pathogens causing powdery mildew, brown rust, and yellow rust.

Regulation of Aegilops tauschii Coss Tiller Bud Growth by Plant Density: Transcriptomic, Physiological and Phytohormonal Responses

Aegilops tauschii Coss is one of the most hazardous weeds that severely infests wheat fields in China. The tillering ability of Ae. tauschii strongly affects the occurrence and spread by influencing its seed output. In this study, Ae. tauschii was sown at low plant density (LPD) and high plant density (HPD) to investigate the effect of plant density on tiller bud outgrowth and its potential regulators using RNA-Seq. Additionally, the chlorophyll content and photosynthesis, soluble sugar and phytohormone levels were also determined at different plant densities. The results showed that an increased plant density significantly inhibited the elongation of tiller buds in the axil of the first leaf at 15 days after planting, with 7.69 mm at LPD and 1.69 mm at HPD. A total of seven putative tiller-related genes were selected and validated using quantitative real-time PCR. Furthermore, chlorophyll levels, photosynthetic efficiency, and soluble sugar contents were distinctly inhibited by HPD in Ae. tauschii, which may be responsible for the restriction of tiller bud growth. In addition, differentially expressed genes (DEGs) were markedly enriched in indole-3-acetic acid (IAA), abscisic acid (ABA), and gibberellin metabolism and signaling. Accordingly, the levels of ABA and gibberellin A3 in Ae. tauschii were strikingly higher at HPD compared with those at LPD, yet the reverse tendency was observed for IAA. Undoubtedly, such results will be highly beneficial for illuminating the underlying regulators of the Ae. tauschii tillering response to plant density and may provide new ideas for the control of this weed in the future.

The basis of resistance mechanism to mesosulfuron-methyl in Tausch's goatgrass (Aegilops tauschii Coss.)

Tausch's goatgrass (Aegilops tauschii Coss.) is one of the most troublesome weeds in winter wheat-growing regions of China. In recent years, the recommended field rate of mesosulfuron-methyl failed to control the Tausch's goatgrass population in Shanxi province (SX), China. Experiments were conducted to characterize the herbicide resistance level and investigate the basis of mesosulfuron-methyl resistance in Tausch's goatgrass. Whole-plant dose-response tests showed that the SX population exhibited 11.42-fold resistance to mesosulfuron-methyl than the susceptible HN population, and the resistance level in the SX population could be significantly reduced by malathion, a cytochrome P450 inhibitor. The SX population also exhibited cross-resistance to imazethapyr, pyroxsulam and bispyribac‑sodium. Acetohydroxyacid synthase (AHAS) sequencing and enzyme activity assays demonstrated that the mesosulfuron-methyl resistance was not conferred by target-site substitution. A sensitive AHAS, together with the malathion revisable resistance, suggested that herbicide metabolism likely plays a main role in the mechanism of mesosulfuron-methyl resistance in the SX population. To our knowledge, this is the first report elucidating the mesosulfuron-methyl resistance in Tausch's goatgrass.