Location: Wheat, Sorghum and Forage Research
2022 Annual Report
Objectives
Objective 1: Identify candidate viral and host genes, through use of mutational analysis, protein-protein interaction, and genomic studies for enhanced control and management of Wheat streak mosaic and Triticum mosaic viruses.
Objective 2: Develop and characterize transgenic wheat for resistance to WSMV and TriMV, and pyramid transgenes with natural resistance genes.
Objective 3: Identify, characterize, and deploy biologically active peptides and genes from the primary and secondary gene pool of wheat for resistance to viral, fungal, and bacterial diseases of wheat.
Objective 4: Develop and characterize adapted winter wheat germplasm with broad and specific disease resistance, and with improved grain nutritional quality.
Objective 5: Develop scab resistant winter barley and winter wheat germplasm.
Approach
The primary objectives of this project are to develop improved wheat germplasm by enhancing disease resistance and grain quality traits. The project will characterize genes of Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) responsible for pathogenicity and vector transmission. This information will be used to develop transgenic wheat with resistance to both viruses, and to the common vector, the wheat curl mite. The project also will use TriMV to express biologically active peptides in wheat, to effect control of bacterial and fungal diseases. Natural (non-transgenic) sources of virus resistance will be used to develop and select germplasm with such resistance, and distribute it to breeding programs world-wide. The project will complete the evaluation and distribution of wheat breeding materials with resistance to Ug99 forms of stem rust, and with low levels of grain phytic acid. The latter will lead to wheat with improved mineral nutrition and diminished anti-nutrient properties. Developed germplasm will be characterized and distributed via the USDA-ARS Lincoln coordinated Winter Wheat Performance Nursery Program. The project consists of three integrated components: germplasm development and evaluation, viral genetics, and plant pathology. Molecular and conventional methodologies will be utilized, and the project scale will range from DNA molecules to field-level. The project also has extensive formal and informal collaborations enhancing our ability to conduct this research. Anticipated products include improved wheat germplasm for the wheat seed industry with value-added traits and biotic stress tolerance, and new targets to continue the laudable goal of developing host-plant resistance.
Progress Report
Objective 1. Wheat streak mosaic virus (WSMV) is an economically important wheat virus in the Great Plains region. Previously, it has been demonstrated that WSMV with complete deletion of helper component proteinase (HC-Pro) gene is viable but changing a single amino acid abolishes systemic infection in wheat. The mechanism behind this anomaly was examined through protein secondary structure predictions, deletion mutations, and biochemical analyses. The N-terminal region of HC-Pro contains mostly a helical region, while the central and C-terminal regions consist of coiled and strand secondary structures. Deletion of amino acids comprising helical and strand regions but not the coiled region of HC-Pro gene resulted in a drastic reduction in the infectivity of WSMV. Additionally, protein interaction studies of all deletion mutants and a single amino acid change mutant showed deletion mutants that failed to infect wheat systemically did not self-interact, which suggests that self-interaction of HC-Pro is crucial for the systemic spread of the virus in wheat.
WSMV coat protein (CP) is involved in wheat streak mosaic disease development. Using antibodies against the WSMV CP, followed by mass spectrometry analyses, identified several wheat proteins interacting with coat protein, including dynamin, purple acid phosphatase, catalase, beta-glucosidase, and dirigent proteins. The biological significance of these proteins in WSMV infection was examined through virus-induced gene silencing. The number of local foci and systemic infection of WSMV were significantly reduced in dynamin- or dirigent-silenced wheat plants, suggesting that these two wheat proteins play an important role in the infection process of WSMV. The dynamin and dirigent genes of wheat could be targeted to develop resistance against WSMV in wheat.
WSMV is transmitted by the wheat curl mite (WCM) in growers’ fields. Previously, we reported that HC-Pro and CP of WSMV are required for WCM transmission. Yeast two-hybrid assay between the WCM cDNA library and CP or HC-Pro revealed that six WCM proteins interacted with CP and HC-Pro proteins of WSMV. The role of these WCM proteins in mite transmission of the virus was examined through the insertion of these mite DNA sequences into WSMV, which revealed that glutathione S transferase and gastric triacylglycerol lipase enzymes of WCM are required for mite transmission of WSMV.
Objective 2. We hypothesized that wheat designed to transgenically express CP or NIa-Pro of WSMV would provide resistance to the virus. The first generation of transgenic wheat showed segregation in a 3:1 ratio for plants with the transgene. The wheat seedlings were screened for resistance against WSMV and found that the NIa-Pro transgenic allele but not CP displayed a resistance phenotype. Wheat seed collected from the T1 generation was used to obtain homogenous wheat lines. Two 4th generation lines containing the transgene continued to show resistance to WSMV. These wheat lines would provide germplasm for the development of WSMV-resistant wheat.
Objective 3: Bacterial leaf streak (BLS) disease, which is caused by Xanthomonas translucens pv. undulosa is an emerging threat to wheat in the Great Plains region. BLS disease can reduce wheat yield by up to 40%, and there is no effective chemical control for the management of this disease. The effect of dual antimicrobial peptides (APMs) on this bacterium was examined through the viral expression of these peptides in wheat. Wheat plants expressing dual AMPs had lesion sizes of 1.4 to 1.8 cm in BLS-inoculated wheat leaves, compared to a virus without the AMP (8.1 cm) and negative control (7.9 cm) wheat. Real-time PCR showed the number of bacteria infecting wheat leaves significantly less in wheat leaves expressing dual AMPs compared to single AMPs or negative control. These data suggest that the expression of dual AMPs significantly enhanced the antimicrobial activity against the BLS pathogen in wheat.
Wheat cv. Mace contains the Wsm1 gene that provides resistance to WSMV at lower temperatures. The Wsm1 gene was originally transferred from intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D. R. Dewy]. However, the presence of a large amount of the wheatgrass genome in Mace resulted in a 15-30% yield drag. To minimize this yield drag, new wheat germplasm was developed, possessing a truncated chromosome from intermediate wheatgrass carrying the Wsm1 resistance gene. Two of the highest-yielding lines from single plot field trials in 2021, possessing the shortened chromosome segment from intermediate wheatgrass, NW13MD108-3 and NW13MD109-1, were screened for WSMV resistance during the 2021 field season. These two lines were rated resistant to WSMV in high disease pressure, confirming the presence of the Wsm1 gene. These two lines were further entered into a WSMV preliminary yield trial for the 2022 field season, along with other high-yielding wheat varieties and other WSMV-resistant lines. Yield trial results revealed no significant differences in seed yield of NW13MD108-3 (44 bu ac-1) and NW13MD109-1 (40 bu ac-1) compared to cultivar ‘Overland’ (42 bu ac-1; UNL cultivar release), ‘Goodstreak’ (43 bu ac-1; UNL cultivar release) and ‘Bob Dole’ (43 bu ac-1; KSU cultivar release). A seed increase for NW13MD108-3 and NW13MD109-1 was harvested in the field during the 2022 field season, enabling these two lines to be evaluated in the 2023 ARS Southern Regional Performance Nurseries.
Objective 4: Effective chemical control of BLS is currently unavailable, and limited genetic resistance to BLS has been found in wheat. In collaboration with a researcher in Fargo, North Dakota, new BLS resistance genes have been identified in the rye genome of triticale and incorporated rye chromosome 5R containing the BLS resistance gene into wheat. Wheat lines with rye chromosome 5R have been developed. These lines have been cross-pollinated to wheat ph1b mutant to shuffle the genes on rye chromosome 5R with wheat chromosomes and eliminate the unwanted genes from rye. We anticipate developing wheat-rye lines that contain the BLS resistance gene but lack the undesired traits of rye. This will lead to the development of the BLS-resistance wheat line that can be used in wheat breeding new resistant varieties.
Ug99-stem rust-resistant wheat breeding lines were developed to mitigate the worldwide threat of this virulent strain of rust. The resistance gene is on the same chromosome segment as Wsm1 and conveys resistance to all known evolved races of Ug99 stem rust. Sixty-eight stem rust-resistant breeding lines were entered into a stem rust preliminary yield trial during the 2022 field season. Ten stem rust-resistant breeding lines, each with yields greater than 45 bu ac-1, outperformed UNL high-yielding check varieties NW13493, Overland, Goodstreak, and KSU cultivar Bob Dole.
Objective 5: Fusarium head blight (FHB), also called scab, is a devastating fungal disease of wheat and barley in the US and worldwide. The major FHB resistance genes were identified mainly in spring wheat, which has limited the progress of deploying those spring wheat-derived resistance genes into winter wheat, especially in the hard red winter wheats. In addition, effective resistance has not been identified in barley. We have integrated a new FHB resistance gene, Fhb7, from tall wheatgrass into wheat chromosome 7B by chromosome engineering (non-GMO approach), which enables the use of Fhb7 to improve common and durum wheat and avoid deleterious effects. Meanwhile, we have also developed DNA markers for Fhb7, which is extremely helpful in deploying Fhb7 in all wheat classes, including hard red winter wheat and durum wheat in the Great Plains regions.
Chromosome-specific DNA markers have been developed for the chromosomes containing the FHB resistance genes. This development will aid in the introgression and characterization of the FHB-resistance genes in a wide range of wheat lines. To date, hundreds of intermediate wheat breeding materials have been produced through cross-pollination and then backcrossed into hard red winter wheat and durum varieties. We set up a new FHB nursery in Lincoln, Nebraska, to evaluate over 300 common wheat and durum wheat lines for FHB resistance. A few durum lines exhibited improved FHB resistance compared to their durum parents. Also, the FHB resistance gene Fhb7 is being transferred from spring wheat to barley using a non-GMO chromosome engineering approach. Multiple wheat genetic stocks have been characterized by chromosome analysis for the introgression of FHB resistance into barley. Ultimately, FHB-resistant winter wheat, durum wheat, and barley plants containing the major spring wheat- and tall wheatgrass-derived resistance genes will be potentially produced and released for variety development, which will protect these cereals from yield loss and grain contamination.
Accomplishments
1. Developed novel high-yielding wheat streak mosaic virus-resistant wheat germplasm derived from intermediate wheatgrass. A reduction in yield is commonly associated with wheat streak mosaic virus (WSMV) resistance gene Wsm1 from intermediate wheatgrass. A new donor line with a reduced Wsm1 translocation was used to develop breeding populations. Wheat lines were screened for WSMV resistance in the field, and a preliminary yield trial experiment was conducted to compare seed yields of the new Wsm1 translocation lines to those of high-yielding check cultivars. ARS scientists in Lincoln, Nebraska, in collaboration with the University of Nebraska-Lincoln scientists, identified two promising breeding lines, NW13MD108-3 and NW13MD109-1, respectively, with seed yields not significantly different (P > 0.05) from high-yielding checks. The new Wsm1 breeding lines will serve as an improved vehicle for the deployment of high-yielding Great Plains wheat varieties with resistance to WSMV.
2. Developed Great Plains-adapted wheat lines with resistance to Ug99 stem rust. A preliminary stem rust yield trial experiment was conducted in 2022 to compare seed yields of new Ug99-resistant breeding lines to previously developed high-yielding varieties. ARS scientists in Lincoln, Nebraska, identified twelve promising stem rust-resistant breeding lines derived from Ug99 resistance sources with grain yields that were not significantly different (P > 0.05) from high-yielding varieties. These twelve wheat lines will be used to develop new wheat cultivars that are resistant to evolved races of Ug99 stem rust and provide security to Great Plains wheat yields from the potential threat of future stem rust epidemics.
Review Publications
Tatineni, S., Alexander, J.A., Qu, F. 2022. Differential synergistic interactions among four different wheat-infecting viruses. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2021.800318.
Qi, L., Cai, X. 2022. Characterization and mapping of a downy mildew resistance gene, Pl36, in sunflower (Helianthus annuus L.). Molecular Breeding. 42. Article 8. https://doi.org/10.1007/s11032-022-01280-1.
Talukder, Z., Underwood, W., Misar, C.G., Seiler, G.J., Li, X., Cai, X., Qi, L. 2022. Genomic insights into Sclerotinia basal stalk rot resistance introgressed from wild Helianthus praecox into cultivated sunflower (Helianthus annuus L.). Frontiers in Plant Science. 13. Article 840954. https://doi.org/10.3389/fpls.2022.840954.
Zhu, X., Boehm Jr, J.D., Zhong, X., Cai, X. 2022. Genomic compatibility and inheritance of hexaploid-derived Fusarium head blight resistance genes in durum wheat. The Plant Genome. 15(2). Article e20183. https://doi.org/10.1002/tpg2.20183.
Venegas, J., Guttieri, M.J., Boehm Jr, J.D., Graybosch, R.A., Bai, G., St. Amand, P.C., Palmer, N.A., Hussain, W., Blecha, S., Baenziger, P. 2022. Genetic architecture of the high inorganic phosphate phenotype derived from a low phytate mutant in winter wheat (Triticum aestivum L.). Crop Science. https://doi.org/10.1002/csc2.20738.
