THE PHENYLALANINE AMMONIA-LYASE GENE FAMILY IN ARABIDOPSIS-THALIANA

Phenylpropanoid derivatives are a complex class of secondary metabolit es that have many important roles in plants during normal growth and i n responses to environmental stress. Phenylalanine ammonialyase (PAL) catalyzes the first step in the biosynthesis of phenylpropanoids, and is usually encoded by a multi-gene family. Genomic clones for three Ar abidopsis thaliana PAL genes containing the entire protein-coding regi on and upstream and downstream sequences have been obtained and comple tely sequenced. Two A. thaliana PAL genes (PAL1 and PAL2) are structur ally similar to PAL genes that have been cloned from other plant speci es, with a single intron at a conserved position, and a long highly co nserved second exon. Previously identified promoter motifs plus severa l additional sequence motifs were found in the promoter regions of PAL 1 and PAL2. Expression of PAL1 and PAL2 is both qualitatively and quan titatively similar in different plant organs and under various inducti ve conditions. A third A. thaliana PAL gene, PAL3, differs significant ly from PAL1 and PAL2 and other sequenced plant PAL genes. PAL3 contai ns an additional intron, and its deduced amino acid sequence is less h omologous to other PAL proteins. The PAL3 promoter region lacks severa l sequence motifs conserved between A. thaliana PAL1 and PAL2, as well as motifs described in other genes involved in phenylpropanoid metabo lism. A. thaliana PAL3 was expressed at very low levels under the cond itions examined.