Comparative genomic analysis of the <i>PAL</i> genes in five Rosaceae species 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 <i>PAL</i> family in Rosaceae plants remains unclear. In this study, we identified 16 <i>PAL</i> homologous genes in five Rosaceae plants (<i>Pyrus bretschneideri</i>, <i>Fragaria vesca</i>, <i>Prunus mume</i>, <i>Prunus persica</i>, and <i>Malus</i> × <i>domestica</i>). We classified these <i>PAL</i>s into three categories based on phylogenetic analysis, and all <i>PAL</i>s were distributed on 13 chromosomes. We tracked gene duplication events and performed sliding window analysis. These results revealed the evolution of <i>PAL</i>s in five Rosaceae plants. We predicted the promoter of the <i>PbPAL</i>s by PLANT CARE online software, and found that the promoter region of both <i>PbPAL1</i> and <i>PbPAL3</i> have at least one AC element. The results of qRT-PCR analysis found that <i>PbPAL1</i> and <i>PbPAL2</i> were highly expressed in the stems and roots, while expression level of <i>PbPAL3</i> was relatively low in different tissues. The expression of <i>PbPAL1</i> and <i>PbPAL2</i> increased firstly and then decreased at different developmental periods of pear fruit. Among them, the expression of <i>PbPAL1</i> reached the highest level 55 days after flowering. Three <i>PbPAL</i>s were induced by abiotic stress to varying degrees. We transfected <i>PbPAL1</i> and <i>PbPAL2</i> into <i>Arabidopsis thaliana</i>, which resulted in an increase in lignin content and thickening of the cell walls of intervascular fibres and xylem cells. In summary, this research laid a foundation for better understanding the molecular evolution of <i>PAL</i>s in five Rosaceae plants. Furthermore, the present study revealed the role of <i>PbPAL</i>s in lignin synthesis, and provided basic data for regulating lignin synthesis and stone cells development in pear plants.