Identification and characterization of phenylalanine ammonia lyase involved in biosynthesis of floral scents in Prunus mume

Floral scent is a significant trait of Prunus mume distinguished with other species of Prunus. And its fragrance is dominated by phenylpropanoids/benzenoids, such as benzyl acetate, cinnamyl acetate and eugenol. In the phenylpropanoids/benzenoids pathway, phenylalanine ammonia-lyase (PAL) is considered to be the first enzyme and plays an important role. However, there are little reports about the characteristics and function of PALs in P. mume. In the present work, two PmPAL genes were screened in the mei's genome, named PmPAL1 and PmPAL2. Phylogenetic tree showed that these two PmPALs clustered together with other PALs from Rosaceae species. Two PmPALs amino acid sequences contained the unique signature motif (GTITASGDLVPLSYIA). Expression pattern analysis showed PmPAL genes expressed all in five tissues, including flower bud, leaf, fruit, root and stem. PmPAL1 expressed higher in root, stem and leaf, while the expression level of PmPAL2 was the highest in flower bud than other tissues. Although the expression levels of PmPAL1 and PmPAL2 all enhanced from budding stage to the full-blooming stage, the RPKM value of PmPAL2 was far more than PmPAL1, suggesting that PmPAL2 might contribute to the phenylpropanoids/ benzenoids biosynthesis in P. mume. Enzyme activity assays showed that PmPAL1 and PmPAL2 all could catalyze phenylalanine (Phe) to produce trans-cinnamic acid (tCA) in vitro. Promoter analysis showed that many cis-elements responsive to the light and hormones presented in the promoter regions of PmPALs. This work illustrates the function of PmPAL genes and lays a foundation on clarifying the molecular mechanism of phenylpropanoids/benzenoids metabolism in P. mume.