Genome-Wide Identification and Expression Pattern Analysis of the Phenylalanine Ammonia-Lyase (PAL) Gene Family in Wheat Under Stripe Rust

Phenylalanine ammonia-lyase (PAL) has been identified as the key rate-limiting enzyme of the phenylpropanoid metabolic pathway, which affects the synthesis of plant secondary metabolites and stress responses. To investigate the composition and function of the PAL gene family in wheat against wheat stripe rust, 54 TaPAL gene family members were identified based on the wheat IWGSC RefSeq v2.1 genome data. Phylogenetic analysis of PAL proteins from wheat, maize, rice, tobacco, and Arabidopsis indicated that wheat PAL genes are more closely related to those of maize and rice. Promoter analysis revealed that these genes contain multiple hormone- and stress-responsive cis-acting elements. To investigate the expression characteristics of the TaPAL family under diverse stress conditions, qRT-PCR was conducted to analyze the transcriptional responses of 24 members distributed across different chromosomes to Puccinia striiformis f. sp. tritici (Pst) infection. Under Pst infection, relatively low basal expression was maintained by most TaPAL genes during early stages, whereas most TaPAL genes were significantly induced at 120 hpi. High expression levels were sustained by most genes at 240 hpi, and decreases were observed at 360 hpi. Four genes selected based on our laboratory’s previous transcriptome data were used for expression analysis under exogenous hormone treatments and abiotic stresses. Diverse expression patterns were exhibited by the TaPAL genes under hormone treatments and abiotic stresses, indicating possible regulatory differentiation among family members. The results provide candidate genes for further functional studies of the wheat PAL gene family in stress responses.