Abstract: Phenylpropanoid derivatives are a complex class of secondary metabolites that have many important roles in plants during normal growth and in responses to environmental stress. Phenylalanine ammonialyase (PAL) catalyzes the first step in the biosynthesis of phenylpropanoids. In the present study, we isolated a novel phenylalanine ammonialyase gene (designated as IiPAL) from tetraploid Isatis indigotica Fort. by rapid amplification of cDNA ends (RACE), which was a cultivar from the diploid plant by genome duplication. The full-length cDNA of IiPAL was 2 530-bp long with an open reading frame (ORF) of 2 178 bp encoding a polypeptide of 725 amino acid residues. Analysis of IiPAL genomic DNA revealed that it was structurally similar to other plant PAL genes, with a single intron at a conserved position, and a long highly conserved second exon. Semi-quantitative RT-PCR revealed that the IiPAL expression in roots and leaves from a tetraploid sample was higher than that in diploid progenitor, whereas expression of IiPAL in stems was almost the same as each other. Furthermore, the highest expression of IiPAL in tetraploid plant was found in roots, which was found in stems in diploid plants. Further expression analysis revealed that gibberellin (GA3), abscisic acid (ABA), methyl jasmonate (MeJA) and cold treatments could up-regulate the IiPAL transcription in tetraploid plants. All our findings suggest that IiPAL participates not only in the defense/stress responsive pathways, but also probably in the polyploidy evolution of I. indigotica.(Author for correspondence. Tel: +86 (0)21 2507 0395; Fax: +86 (0)21 2507 4575; E-mail: chenwanshengsmmu@gmail.com)

Key words: defense/stress, IiPAL, Isatis indigotica, polyploidy, RACE.