Tomato Phenylalanine Ammonia-Lyase Gene Family, Highly Redundant but Strongly Underutilized

Abstract

Phenylalanine ammonia-lyase (PAL) is an important enzyme in both plant development and pathogen defense. In all plants it is encoded by a multi-gene family, ranging in copy number from four in Arabidopsis to a dozen or more copies in some higher plants. Many studies indicate that alternate genes are differentially regulated in response to environmental stimuli. In this study, Southern blot and dot blot analyses in tomato indicate a surprisingly large family of related sequences with ϳ26 copies in the diploid genome, some easily distinguished by restriction enzyme digestion. Analyses of a BAC genome library suggest that the genes are generally not clustered. A more detailed comparison of the gene sequences using PCR to isolate the individual copies and reverse transcription-PCR to study the transcripts that they encode indicates a significant diversity in the gene sequences themselves, but surprisingly only one mRNA transcript can be detected even when additional expression is induced by pathogen growth or wounding. Consistent with previous reports in other plants, a parallel study with a closely related plant, the potato, indicates a much broader utilization of the PAL genes, highlighting the unusual nature of this family in tomato and of the mechanism(s) that silences so many members. Plant transformation analyses further demonstrate the presence of very active silencing, suggesting aggressive competition between PAL gene duplication and copy inactivation during PAL gene evolution.

Enzymes of phenylpropanoid metabolism in the important medicinal plant Melissa officinalis L.

“…Whether the second gene is also actively expressed in suspension cells of M. officinalis is not yet known. In tomato, only one of the numerous isoforms has been shown to be actively formed (Chang et al 2008), whereas the two isoforms from raspberry both are active (Kumar and Ellis 2001). An association of the MoPAL1 expression with the biosynthesis of RA was shown by semiquantitative PCR.…”

Environmental Stresses of Field Growth Allow Cinnamyl Alcohol Dehydrogenase-Deficient Nicotiana attenuata Plants to Compensate for their Structural Deficiencies

“…7, D and E); however, the GH-grown plants showed the reverse trend. PAL is the first rate-limiting enzyme in the phenylpropanoid pathway leading to lignin biosynthesis and is known to be influenced by a variety of growth conditions and stresses (Chang et al, 2008;Olsen et al, 2008;Huang et al, 2010). We hypothesized that field-related stresses could enhance PAL gene expression, which might explain both the higher accumulation of the above-mentioned PAL-derived soluble metabolites and lignin contents of field-grown plants (Tables I and II).…”

cDNA cloning, Phylogenic Analysis and Gene Expression Pattern of Phenylalanine ammonia-lyase in Sugarcane (Saccharum officinarum L.)

“…It is encoded by a small gene family in the plants with four members in Arabidopsis (Huang et al 2010). One exception is the potato PAL gene family, made up of 40-50 genes and the loblolly pine PAL, which has been reported to be encoded by a single gene (Chang and Lim 2008). Using transgenic plants, it has been shown that PAL activity is a major control point for regulating the phenylpropanoid pathway (Shadlea et al 2003) and modulating many secondary metabolites biosynthesis in the plants (Huang et al 2010;Gao et al 2012;Coulon et al 2012).…”