Enzymatic Characterization of Genes in and Overexpression of the .

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) catalyzes the deamination of phenylalanine, which is the initial step in the biosynthesis of phenylpropanoids. It serves as a crucial enzyme that facilitates the transfer of carbon from primary to secondary metabolism in plants. Duckweed is regarded as a promising chassis plant in synthetic biology research and application, due to its being rich in secondary metabolites and other advantages. The genes encoding PAL in (L.) Schleid, the giant duckweed, were investigated in this study. Three genes () were identified and cloned. All of them were successfully expressed in , and their recombinant proteins all showed PAL activity. In addition, SpPAL1 and SpPAL2 proteins could also utilize tyrosine as substrate, although the activity was low. A qRT-PCR analysis demonstrated that the expression of was most pronounced in young fronds. It was found that the expression of and was significantly induced by MeJA treatment. Overexpression of in inhibited the growth of fronds and adventitious roots in the transgenic plants, indicating the importance of in duckweed besides its involvement in the secondary metabolism.