Location: Corn Insects and Crop Genetics Research
2023 Annual Report
Accomplishments
1. Soybean: a new model to study iron deficiency chlorosis (IDC) in plants. IDC negatively affects crop quality and yield. Studies from model species have demonstrated shoot control or influence of iron uptake in roots. However, these studies were conducted days and weeks after the onset of iron stress. ARS scientists in Ames, Iowa, used grafting of nearly identical soybean lines Clark and IsoClark (iron stress tolerant and susceptible, respectively), to demonstrate the Clark rootstock can drive iron stress tolerance in IsoClark leaves. In contrast, IsoClark rootstock is unable to confer iron stress tolerance in Clark leaves. RNA-seq analyses of grafted plants 30 and 120 minutes after iron stress identified 518 and 846 differentially expressed genes in leaves and roots, respectively. Grafts with a Clark rootstock induced genes involved in iron uptake and utilization at 30 minutes in the root and by 120 minutes in the leaves, regardless of the leaf genotype. This suggests an unknown mobile signal, initiated in roots, regulates iron stress responses in soybean leaves. Better understanding of the complex differences between crop and model species will aid in the development of crops with improved IDC tolerance, reducing farmer losses and increasing yield.
2. Identification of Rpp3, a nucleotide binding site-leucine rich repeat (NBS-LRR) protein that confers resistance to Phakopsora pachyrhizi in soybean. Soybean rust, caused by the fungus Phakopsora pachyrhizi, is an economically important disease that negatively impacts soybean production throughout the world. Yield losses as high as 80% have been reported. While most soybean germplasm is susceptible, seven genetic regions have been identified that provide resistance to P. pachyrhizi (Rpp1 to Rpp7). Rpp3 was first discovered and characterized in the soybean accessions PI 462312 and PI 506764. To identify Rpp3, ARS scientists from Ames, Iowa, and Fort Detrick, Maryland, in collaboration with Iowa State University, amplified and sequenced five Rpp3 candidate genes from each resistant line. Conserved regions from the ten genes were used to develop virus induced gene silencing constructs that were able to knock down expression of the candidate genes and compromise resistance to P. pachyrhizi. Gene expression analysis and sequence comparisons of the Rpp3 candidate genes in PI 462312 and PI 506764 suggest that a single candidate gene, Rpp3C3, is responsible for Rpp3-mediated resistance. This research will allow breeders to rapidly differentiate between known and potentially novel Rpp3 alleles, facilitating the breeding of durable resistance.
3. Iron stress tolerant soybean line, Fiskeby III, utilizes novel genes and pathways in response to iron deficiency stress. Iron deficiency negatively impacts plant yield, so to improve plant tolerance, new sources of stress tolerance need to be identified and integrated into breeding programs. Fiskeby III is a soybean line resilient to multiple abiotic stresses, including iron deficiency. Building on previous research, ARS scientists in Ames, Iowa, silenced a novel gene associated with iron deficiency stress tolerance and subjected silenced and control Fiskeby III plants to stress conditions for either one day or seven days. Analysis of whole genome expression profiling revealed Fiskeby III responds quickly to iron deficiency stress, inducing phosphate deficiency responses to re-establish nutrient homeostasis within the plant. Fiskeby III induces the canonical soybean iron deficiency responses, but utilizes different molecular pathways, shifts the timing of the responses, and employs genes unique to Fiskeby III. Identifying and characterizing these genes and pathways in Fiskeby III provides novel targets for breeding elite soybean lines with improved stress tolerance which will increase yield and farmer profits.
Review Publications
Karhoff, S., Vargas-Garcia, C., Lee, S., Mian, R.M., Graham, M.A., Dorrance, A., McHale, L. 2022. Identification of candidate genes for a major quantitative disease resistance locus from soybean PI 427105B for resistance to phytophthora sojae. Frontiers in Plant Science. 13. Article 893652.
O'Rourke, J.A., Graham, M.A. 2022. Coupling VIGS with short and long-term stress exposure to understand the Fiskeby III iron deficiency stress response. International Journal of Molecular Sciences. 24(1).Article 647. https://doi.org/10.3390/ijms24010647.
