Cloning and characterisation of a phenylalanine ammonia-lyase gene from Rhus chinensis

Abstract

The gene and cDNA sequence encoding PAL from Chinese medicinal plant Rhus chinensis were cloned and analyzed, furthermore the biochemical properties, kinetic parameters, differential expression and key sites were studied. Rhus chinensis is a well-known Chinese medicinal plant. Phenylalanine ammonia-lyase (PAL) is the first enzyme of phenylpropanoid pathway. Several recent studies suggested that PAL also play an important role in plant-aphid interaction. In this study, both the cDNA and the genomic sequence encoding PAL from Rhus chinensis (designated as RcPAL) were cloned and analyzed. The 3,833bp gene contained a 1,342bp intron and two extrons. The ORF was 2,124bp and predicted to encode a 707-amino acid polypeptide. The results of real-time PCR showed that RcPAL expressed in all tested tissues and followed the order: stems>young leaves>petioles>roots>seeds>mature leaves. RcPAL was successfully expressed in E. coli with the pET-28a-RcPAL recombinant vector. The recombinant protein exhibited a high level of PAL activity. Biochemical properties and kinetic parameters of recombinant RcPAL were further studied. The results showed that the optimal temperature and pH for RcPAL activity were 45°C and 9.0, and the K m and K cat values were 7.90mM and 52.31s(-1), respectively. The active sites and substrate selectivity site were also investigated with site-directed mutagenesis methods, suggesting that Phe(126) is responsible for the substrate selectivity. To our knowledge, this was the first full-length PAL gene cloned and characterized from the family Anacardiaceae so far.