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Title:   Author  item
                                            Sullivan, Michaelitem
                                            THOMA, SHARON - EDGEWOOD COLLEGEitem
                                            Samac, Deborah

                                                         - *Debby*item
                                            Hatfield, Ronald
  Submitted to: Molecular Breeding of Forage and Turf Conference
                                    Publication Type: Book / Chapter
                                    Publication Acceptance Date: 5/13/2003
                                    Publication  Date: 4/1/2004
                                    Citation: Sullivan, M.L., Thoma, S., Samac, D.A., Hatfield, R.D. 2004. Cloning of red clover and alfalfa polyphenol oxidase genes and expression of active enzymes in transgenic alfalfa. In: Hopkins, A., Wang, Z-Y., Mian, R., Sledge, M., Barker, R.W. editors.  Molecular Breeding of Forage and Turf. Netherlands: Kluwer Academic Publishers. p. 189-195.Interpretive Summary:
                                Technical Abstract: Red clover contains high levels of polyphenol oxidase (PPO) activity and o-diphenol substrates. This results in a characteristic post-harvest browning reaction associated with decreased protein degradation during ensiling. To define PPO's role in inhibition of post-harvest proteolysis, we are taking both biochemical and molecular approaches. We have cloned three unique PPO cDNAs from red clover leaves, RC PPO1-3. The cDNAs encode proteins that are predicted to be targeted to the chloroplast thylakoid lumen. RNA blotting and immunoblotting experiments indicate RC PPO1 is expressed predominantly in young leaf tissue, RC PPO2 is expressed most highly in flowers and petioles, and RC PPO3 is expressed in both leaves and flowers. Using a transgenic approach, we expressed the red clover cDNAs in talfalfa, which lacks both significant endogenous PPO activity and o-diphenol substrates in its leaves, to further characterize the individual proteins encoded by RC PPO1-3. The expressed proteins are active in alfalfa extracts and the individual enzymes show differences in substrate specificity, suggesting different functional roles. Additionally, we have cloned a PPO gene from alfalfa. Preliminary studies indicate endogenous alfalfa PPO expression is limited to flowers and seedpods. Expression of the cloned alfalfa PPO gene from a strong constitutive promoter in transgenic alfalfa results in low but measurable enzyme activity, suggesting a low specific activity compared to the red clover enzymes.


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