Molecular analysis and expression of phenylalanine ammonia-lyase from poinsettia (<i>Euphorbia pulcherrima</i> willd.)

Abstract

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) is a key regulatory enzyme that link primary and secondary metabolism in plants by catalyzing the conversion of l-phenylalanine to cinnamic acid. In this study, the cDNA and genomic DNA of PAL (named EpPAL) in poinsettia (Euphorbia pulcherrima willd.) were isolated and submitted in GenBank with accession number FJ594466 and FJ943503, respectively. The full-length of cDNA was 2429 bp with a poly (A) tail and contains a 2166-bp open reading frame (ORF) encoding 721 amino acids. The sequence of genomic DNA was 3315 bp, and the transcript was divided into two exons by an 886-bp long intron which located at 416 bp downstream initiation codon. Expression analysis of EpPAL in poinsettia revealed that expression levels were higher in roots and bracts, but lower in stems and green leaves. Meanwhile, expression levels increased in the order: green leaves - turning color leaves - bracts, which were consistent with their anthocyanin content during growth and development of bracts. The curve of diurnal variation of EpPAL expression level in bracts exhibited two highest peaks at 9:00 and 18:00, respectively, and reached the lowest level at 12:00 in a clear day. With the maturation and senescence of bracts, expression levels reduced gradually in both green leaves and bracts, but decreased more rapidly in bracts than green leaves.

Keywords: Cloning, expression, phenylalanine ammonia-lyase, poinsettia