Differential expression of phenylalanine ammonia lyase (PAL) genes implies distinct roles in development of graft incompatibility symptoms in Prunus.

Abstract

Biosynthesis of phenolic compounds occurs via the phenylpropanoid pathway, in which the phenylalanine ammonia-lyase (PAL) acts as a key-control enzyme. In this study, two apricot PAL genes (ParPAL1 and ParPAL2) were isolated and characterized by screening an apricot genome library. The two full-length cDNAs encoding both isoforms were isolated using RACE-PCR. Amino acid sequence alignments and phylogenetic analysis showed that apricot PALs were highly homologous with their orthologues in other plants. The expression patterns of the two genes were investigated in developing callus unions with different degree of compatibility at two time points after grafting (10 and 21 DAG). The results indicated that ParPAL1 and ParPAL2 transcripts were differentially expressed between compatible and incompatible unions throughout graft development. ParPAL1 transcripts were 3- fold more abundant in incompatible unions than those of compatible one at 10 and 21 DAG, whereas ParPAL2 transcripts were induced in graft incompatible unions at 21 DAG. The comparison of the level of the two transcripts between various tissues (bark, leaves and callus tissue) showed that ParPAL1 transcripts were 3-fold more abundant that those of ParPAL2 in callus tissue, suggesting the involvement of ParPAL1 in the synthesis of flavonoids.