Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2014
Publication Date: 11/20/2014
Citation: Fuerst, P.E., Okubara, P.A., Anderson, J.V., Morris, C.F. 2014. PPO as a component of seed defense against pathogens. Frontiers in Plant Science. 5:689.
Interpretive Summary: This review is directed towards understanding biochemical and molecular seed-microbe interactions and towards developing seed decay as an ecological approach to selective management of weedy and invasive species. Seeds have physical, chemical, and biological mechanisms to defend their food reserves, hence germination ability, against decay microorganisms. Polyphenol oxidases are commonly associated with plant defense, and have been identified as components of dormant cereal seed coats that, at least in wild oat, are activated during interactions with soilborne fungal pathogens. Dormant seeds of wild oat are resistant to decay by fungal pathogens, and their ability to mobilize polyphenol oxidases to the seed coat exterior may play a significant role. The review contains original and new findings on features of polyphenol oxidases from wheat seeds that direct the proteins to specific locations in the plant cell, including the exterior.
Technical Abstract: Dormant seeds in the soil are subjected to decay from soil microorganisms, and mount a defense response when challenged by soilborne pathogens and pests. Seeds of wild oat are particularly resistant to decay, and induction of polyphenol oxidases (PPO) is hypothesized to be one of the biochemical seed defense mechanisms. This review presents current knowledge about the PPO gene family in cereals and molecular mechanism(s) of induction and activation of polyphenol oxidase by seed-decaying Fusarium fungi. Polyphenol oxidase from wild oat is activated by proteolytic cleavage, which renders the protein soluble, hence leachable, from the caryopsis to the exterior of the seed coat. Preliminary data suggest that peroxidase, chitinase, and oxalate oxidase may also be induced, implying that multiple components are involved in seed defense. Microbial (biological) control as a sustainable approach to reducing weed seeds in the seed bank of agroecosystem soils is discussed.