Functional and kinetics of two efficient phenylalanine ammonia lyase from Pyrus bretschneideri

The enzyme phenylalanine ammonia lyase (PAL) controls the transition from primary to secondary metabolism by converting L-phenylalanine (L-Phe) to cinnamic acid. However, the function of PAL in pear plants (Pyrus bretschneideri) has not yet been fully elucidated.

We identified three PAL genes (PbPAL1, PbPAL2 and PbPAL3) from the pear genome by exploring pear genome databases. The evolutionary tree revealed that three PbPALs were classified into one group. We expressed PbPAL1 and PbPAL2 recombinant proteins, and the purified PbPAL1 and PbPAL2 proteins showed strict substrate specificity for L-Phe, no activity toward L-Tyr in vitro, and modest changes in kinetics and enzyme characteristics. Furthermore, overexpression of PbAL1 and PbPAL1-RNAi, respectively, and resulted in significant changes in stone cell and lignin contents in pear fruits. The results of yeast one-hybrid (Y1H) assays that PbWLIM1 could bind to the conserved PAL box in the PbPAL promoter and regulate the transcription level of PbPAL2.

Our findings not only showed PbPAL's potential role in lignin biosynthesis but also laid the foundation for future studies on the regulation of lignin synthesis and stone cell development in pear fruit utilizing molecular biology approaches.