Isolation and characterization of arginase promoters in loblolly pine (Pinus taeda L.) and Arabidopsis thaliana

Arginase hydrolyzes the amino acid arginine and produces the non-protein amino acid omithine and urea. In plants, arginase has been associated with the mobilization of seed storage reserves to provide the seedling with nutrients. To understand how arginase is regulated in loblolly pine we isolated two upstream regions that both contain an intron in the 5' UTR and several sets of repeated sequences. PCR using individual megagametophytes indicated that these upstream regions either represent two genes that are closely linked or are alleles of a single gene.;In angiosperms, arginase, in addition to its role in early seedling growth, has also been found in non-seed related tissues. In the model angiosperm, Arabidopsis thaliana, there are two arginase genes (ARGAH1 and ARGAH2). We isolated the upstream regions of each Arabidopsis arginase and placed each in front of a GUS reporter gene and generated transgenic plants. We observed staining in immature leaves of seedlings and rosette stage plants and in several floral organs. Plants containing the largest ARGAH1 fragment stained the pollen and this expression of ARGAH1 in pollen was confirmed by quantitative PCR. We also identified two types of cis-acting elements that may have a role in the expression of ARGAH1 in pollen.;In tomato, one of the arginase genes has been shown to be induced in response to wounding and MeJA treatment. We have shown that Arabidopsis is similar in this respect as ARGAH2 is responsive to wounding and MeJA. We also completed microarrays comparing argah2 plants to wild-type plants in both control and MeJA treated plants to identify genes that were differentially expressed. We identified several genes including a pathogenesis related gene (PR-1). PR genes are frequently used as markers for the induction of pathogenesis in plants.;Together these data show that arginase may have roles in defense, early leaf, floral and pollen development. These are in addition to arginase's already described role in seed storage reserve mobilization. Thus, arginase is an enzyme involved in several important and diverse physiological processes in plants.