A genomic cluster containing four differentially regulated subtilisin-like processing protease genes is in tomato plants

Abstract

Screening of a genomic library from tomato plants (Lycopersicon esculentum) with a cDNA probe encoding a subtilisin-like protease (PR-P69) that is induced at the transcriptional level following pathogen attack (Tornero, P., Conejero, V., and Vera, P. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 6332-6337) resulted in the isolation of a cluster of genomic clones that comprise a tandem of four different subtilisin-like protease genes (P69A, P69B, P69C, and P69D). Sequence analyses and comparison of the encoded proteins revealed that all are closely related (79 to 88% identity), suggesting that all are derived from a common ancestral gene. mRNA expression analysis as well as studies of transgenic plants transformed with promoter-beta-glucuronidase fusions for each of these genes revealed that the four genes exhibit differential transcriptional regulation and expression patterns. P69A and P69D are expressed constitutively, but with different expression profiles during development, whereas the P69B and P69C genes show expression following infection with Pseudomonas syringae and are also up-regulated by salicylic acid. We propose that these four P69-like proteases, as members of a complex gene family of plant subtilisin-like proteases, may be involved in a number of specific proteolytic events that occur in the plant during development and/or pathogenesis.