Activation of Polyphenol Oxidase in Dormant Wild Oat Caryopses by a Seed-Decay Isolate of Fusarium avenaceum

Authors: Anderson, James; FUERST, E PATRICK - Washington State University; TEDROW, TRISA - Kansas State University; Hulke, Brent; Kennedy, Ann

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2010
Publication Date: 10/13/2010
Citation: Anderson, J.V., Fuerst, E., Tedrow, T., Hulke, B.S., Kennedy, A.C. 2010. Activation of polyphenol oxidase in dormant wild oat caryopses by a seed-decay isolate of Fusarium avenaceum. Journal of Agricultural and Food Chemistry. 58:10597-10605.

Interpretive Summary: Defense responses are one component important for persistence of dormant weed-seeds in the soil seed bank. In this study, we report on a seed-decay pathogen that induces activity of a plant defense enzyme called polyphenol oxidase in seeds of wild oat. This enzyme plays a role in converting metabolic substrates such as phenolics into antimicrobrial compounds. Our data suggests that exposure of wild oat seed to a seed-decay pathogen activates polyphenol oxidases by causing inactive forms of the enzyme to be processed into several smaller pieces that have increased activity. These smaller, activated forms of the enzyme have also have increased solubility and can more freely move out of the seeds. We propose that this defense response process plays an important role for establishing a protective barrier to pathogen attack in wild oat seeds.

Technical Abstract: Incubation of dormant wild oat (Avena fatua L., isoline M73) caryopses for 1 to 3 days with Fusarium avenaceum seed-decay isolate F.a.1 induced activity of the plant defense enzyme polyphenol oxidase (PPO). Both extracts and leachates obtained from F.a.1-treated caryopses had decreased abundance of an ~57 kD antigenic PPO and increased abundance of antigenic PPOs ranging from ~52 to 14 kD, compared to extracts and leachates from untreated caryopsis. Leachates from caryopsis incubated 2 days with F.a.1 also had 5.1- and 7.5-fold more total PPO activity gfwt-1, and specific activity, respectively. Fractionation of leachate proteins by ion-exchange chromatography associated the majority of PPO activity with an ~36 kD protein from untreated caryopses, and ~36, 25, and 24 kD proteins from F.a.1-treated caryopses. Predicted peptide sequences obtained from HPLC-MS/MS analyses indicated the ~57 and 36 kD wild oat proteins had strong similarity to wheat PPO. However, the 25 and 24 kD proteins were most similar to a chitinase and oxalate oxidase, respectively. Our results suggest that F.a.1 induces activation of latent PPO near the surface of wild oat caryopsis through a mechanism involving cleavage of a C-terminal PPO peptide, and may be part of a defense response that mobilizes pathogen-defense proteins to establish a protective barrier around the caryopses.