Isolation and Characterization of a Gene Encoding a PR-1-Like Protein from Arabidopsis thaliana

Abstract

The hypersensitive (resistance) response to infection by pathogens is accompanied by the synthesis of a variety of host proteins, several of which are termed PR3 proteins. Although the activities of some PR proteins suggest that they are antifungal agents (5, 6), the functions of other families of PRs, including the PR1 proteins, are unknown. The PR1 proteins have been well characterized in terms of sequence, cellular localization, and synthesis in tobacco and tomato. Circumstantial evidence suggests that they may be involved in both the hypersensitive response and systemic acquired resistance (for reviews, see refs. 1 and 3), and recently it has been demonstrated that they are also synthesized during normal floral development in tobacco (7). Because of the difficulties of studying complex phenomena in higher plants such as tobacco, we want to develop Arabidopsis thaliana as a model system for studying the hypersensitive response. As a first step toward using A. thaliana as a model system and also helping to determine the function of PR-I proteins, PR-I like genes from Arabidopsis were isolated. A tobacco PRlb cDNA clone (2) was used as a probe to isolate two genomic clones from Arabidopsis. Although both clones hybridize to the tobacco PRI genes, they do not cross-hybridize with each other, suggesting that there is extensive sequence diversity between the two genes. Each hybridizes on a genomic Southern blot to only one size fragment, indicating that these are both likely single-copy genes. The sequence of one of these two genomic clones (GI 9) is reported here (Fig. 1). The clone contains a 528-nucleotide open reading frame that begins with a presumptive signal peptide of 43 amino acids. The remaining segment of this open reading frame shows a high level of homology to tobacco PR-I and to a tomato P14 sequence (Table 1). The similarity in size and sequence of the predicted protein with PR-I and p14, together with the presence of a consensus TATA motif at approximately 80 base pairs 5' upstream of the initiating AUG, suggests that this is a functional gene. However, at this point, expression of either the RNA or the protein has not been confirmed. 'This work was supported by grant No. DCB-90037 11 from the National Science Foundation. 2Cuffent address: Department of Plant Pathology, Cook College, Rutgers University, New Brunswick, NJ 08903. 'Abbreviation: PR, pathogenesis related.