Phenylalanine ammonia lyase genes in red clover: Expression in whole plants and in response to yeast fungal elicitor

In red clover (Trifolium pratense L.) four unique cDNAs encoding phenylalanine ammonia lyase (PAL, EC 4.3.1.5) were identified (PAL1-4). PAL2-4 encode nearly identical proteins (> 97 %) that are only 89 % identical to that encoded by PAL1. Under normal growing conditions, in young leaves and flowers PAL1 mRNA accumulates to higher levels than that of PAL2-4 whereas in mature leaves and stems, mRNA levels are similar for PAL1 and PAL2-4. Treatment of red clover seedlings with yeast elicitor preparation results in an approximately six-fold induction of PAL2-4 transcripts within 1 h of treatment but only a modest induction of PAL1 transcripts. These results suggest that while both classes of enzymes play a role in biosynthesis of phenylpropanoid compounds under normal growing conditions, PAL2-4 enzymes are also involved in pathogen defense responses.