Genome-wide analysis of phenylalanine ammonia-lyase (PAL) gene family in five Rosaceae plants and expression analysis and functional identification of Chinese white pear

Abstract

Phenylalanine ammonia lyase (PAL) plays an important role in the biosynthesis of secondary metabolites regulating plant growth response. To date, the evolutionary history of the PAL family in Rosaceae plants remains unclear. In this study, we identified 16 PAL homologous genes in five Rosaceae plants (Pyrus bretschneideri, Fragaria vesca, Prunus mume, Prunus persica, and Malus × domestica). We classified these PAL genes into three categories based on phylogenetic analysis，and all PAL genes were distributed on 13 chromosomes. Subsequently, we track gene replication events and perform sliding window analysis. These results revealed the evolution of PAL genes in five Rosaceae plants. We predicted the promoter of the PbPAL genes by PLANTR CARE online software, and found that the 5'regulatory region of both PbPAL1 and PbPAL3 has at least one AC element motif. The results of qRT-PCR analysis found that PbPAL1 and PbPAL2 were highly expressed in the stem and root , while expression level of PbPAL3 was relatively low in different tissues. The expression of PbPAL1 and PbPAL2 genes increased firstly and then decreased at different developmental periods of pear fruit. Among them, the expression of PbPAL1 reached the highest level 55 days after flower. Three PbPAL genes were induced by abiotic stress to varying degrees. We transfected PbPAL1 and PbPAL2 genes into Arabidopsis thaliana, resulting in lignin content increased significantly and thick cell wall of intervascular fibers and xylem cells. In summary, This study laid a foundation for better understanding the molecular evolution of PAL genes in five Rosaceae plants. Furthermore, the present study revealed the role of PbPAL genes in lignin synthesis, and provided basic data for regulating lignin synthesis and stone cell development of pear.