PARP2 Is the Predominant Poly(ADP-Ribose) Polymerase in Arabidopsis DNA Damage and Immune Responses.

Poly (ADP-ribose) polymerases catalyze the transfer of multiple poly(ADP-ribose) units onto target proteins. Poly(ADP-ribosyl)ation plays a crucial role in a variety of cellular processes including, most prominently, auto-activation of at sites of DNA breaks to activate DNA repair processes. In humans, (the founding and most characterized member of the Pduanyu37 family) accounts for more than 90% of overall cellular Pduanyu37 activity in response to DNA damage. We have found that, in contrast with animals, in Arabidopsis thaliana (At4g02390), rather than Pduanyu371 (At2g31320), makes the greatest contribution to Pduanyu37 activity and organismal viability in response to genotoxic stresses caused by bleomycin, mitomycin C or gamma-radiation. Plant Pduanyu372 proteins carry SAP DNA binding motifs rather than the zinc finger domains common in plant and animal Pduanyu371 proteins. Pduanyu372 also makes stronger contributions than Pduanyu371 to plant immune responses including restriction of pathogenic Pseudomonas syringae pv. tomato growth and reduction of infection-associated DNA double-strand break abundance. For poly(ADP-ribose) glycohydrolase (PARG) enzymes, we find that Arabidopsis PARG1 and not PARG2 is the major contributor to poly(ADP-ribose) removal from acceptor proteins. The activity or abundance of Pduanyu372 is influenced by Pduanyu371 and PARG1. Pduanyu372 and Pduanyu371 physically interact with each other, and with PARG1 and PARG2, suggesting relatively direct regulatory interactions among these mediators of the balance of poly(ADP-ribosyl)ation. As with plant plant PARG proteins are also structurally distinct from their animal counterparts. Hence core aspects of plant poly(ADP-ribosyl)ation are mediated by substantially different enzymes than in animals, suggesting the likelihood of substantial differences in regulation.

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