Poster: Enzymology

Abs # 240: Regulation of tomato arginase by wounding, jasmonate, and the phytotoxin coronatine

Presenter:	Chen, Hui , chenhui@msu.edu
Authors	Chen, Hui  (A)   McCaig, Bonnie C (A)   Melotto, Maeli  (A)   Liu, Guanghui  (A)   He, Sheng Yang  (A) (B)  Howe, Gregg A (A) (C)
Affiliations:	(A): Department of Energy-Plant Research Laboratory (B): Department of Plant Biology (C): Department of Biochemistry and Molecular Biology, Michigan State University

Regulated expression of arginase in mammalian cells plays an important role in controlling L-arginine availability for the biosynthesis of polyamines, nitric oxide (NO), and other essential metabolites. The potential role of arginase as a metabolic control point in higher plants, which also utilize L-arginine for the production of polyamines and NO, has not been investigated. Here, we report the characterization of two genes (LeARG1 and LeARG2) from Lycopersicon esculentum (tomato) that encode arginase. Phylogenic analysis showed that LeARG1 and 2, like all other putative plant arginases, are more similar to agmatinase than to non-plant L-arginases. Nevertheless, recombinant LeARG1 and 2 showed a strong substrate preference for L-arginine over agmatine and related guanidino compounds. As is the case for mammalian arginase, the NO precursor NG-hydroxy-L-arginine (L-NOHA) was a potent inhibitor of recombinant LeARGs and native arginase from tomato leaves. LeARG1 and LeARG2 transcripts accumulated to their highest levels in reproductive tissues of healthy plants. LeARG2 expression, together with arginase activity, was strongly induced in leaves in response to mechanical wounding and the plant defense signal, methyl jasmonate. Infection of tomato leaves with Pseudomonas syringae pv. tomato also induced LeARG2 mRNA accumulation and arginase activity. Arginase expression in response to P. syringae was mediated by the bacterial phytotoxin coronatine, a virulence factor that mimics the action of jasmonate. These results suggest a role for arginase in plant responses to biotic stress, and highlight striking similarities in arginase regulation during host defense responses of plants and animals.