A diverse family of phenylalanine ammonia-lyase genes expressed in pine trees and cell cultures

Using degenerate PCR primers that target evolutionarily conserved sequences in pal genes, we show that in the gymnosperm, Pinus banksiana, phenylalanine ammonia-lyase (PAL) is encoded by a multigene family of at least eight to ten loci. Five classes of pal sequence were easily distinguished among 28 clones sequenced from the products of PCR amplification of haploid genomic DNA. The dominant sequence from each class was named, yielding pall to pal5 loci. These genes shared 68.8% to 94.0% nucleotide identity over the 366 bp region compared. All of pall to pal5 were expressed in cell suspension cultures treated with a fungal elicitor and all but pal3 were expressed in differentiating xylem tissue of a mature tree. Only pal1 was expressed in unelicited cell cultures. While these P. banksiana genes are quite divergent, they are still more similar to each other than to any angiosperm pal gene cloned to date. For its roles in development and defense, PAL production in P. banksiana is coordinated from a large, diverse multigene family. We discuss evidence suggesting that other pines have similar pal gene family structures.