BIOCHEMICAL AND MOLECULAR REGULATION OF DEFENSE RESPONSES TO A PATHOGENIC SOIL FUNGUS IN DORMANT SEEDS
Pollard, A.T.1, Okubara, P.2, James, M.1 and Fuerst, E.P.1,3
1Department of Crop and Soil Sciences, Washington State University, Pullman, Washington, USA
2USDA-ARS, Wheat Health, Genetics and Quality Research Unit, Pullman, Washington, USA 3Western Wheat Quality Laboratory, Washington State University, Pullman, Washington, USA
Contact: Annie Pollard, email@example.com
Dormancy and decay resistance of weed seeds in the soil seedbank challenge long-term weed management. Dormant seeds employ various physical and chemical defenses to inhibit seed decay pathogens, but little is known about biochemical seed defenses.
We evaluated activities of the defense enzymes polyphenol oxidase, peroxidase, exochitinase, and oxalate oxidase produced by dormant wild oat (Avena fatua) and wheat (Triticum aestivum) seeds in response to the pathogenic soil fungus Fusarium avenaceum isolate ‘F.a.1’. Caryopsis decay was scored with a visual assessment and quantitative real-time PCR was used to evaluate seed defense responses at the transcriptional level. Additionally, quantitative PCR was used to measure the extent of F.a.1 infection in seeds and soil at various time points. Activities of the degradative fungal enzymes protease and xylanase were measured in soil and wild oat caryopses throughout the course of infection. Experiments were conducted both in vitro on agar plates and in soil.
We found that F.a.1 induced the seed defense enzymes polyphenol oxidase, peroxidase, and exochitinase, but inhibited activity of oxalate oxidase. Moreover, wild oat and wheat seed responses to F.a.1 infection were similar qualitatively, but different quantitatively. Preliminary qRT-PCR results indicate that F.a.1 induces polyphenol oxidase, exochitinase, and NADPH oxidase, but not oxalate oxidase, at the transcriptional level in wild oat and/or wheat. Fungal abundance in seeds and soil and activities of F.a.1-derived degradative enzymes increased over time of infection.
Our results suggest that biochemical and molecular defense responses may contribute to the prolonged survival of wild oat and other weed species in the soil seedbank. These results warrant further investigation of fungal-induced seed decay as a potential alternative approach to managing the dormant weed seedbank in the soil.