The polyphenol oxidase gene family in land plants: Lineage-specific duplication and expansion
Date
2012-08-16
Authors
Tran, Lan T
Taylor, John S
Constabel, C. Peter
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: Plant polyphenol oxidases (PPOs) are enzymes that typically use molecular oxygen to oxidize
ortho-diphenols to ortho-quinones. These commonly cause browning reactions following tissue damage, and may
be important in plant defense. Some PPOs function as hydroxylases or in cross-linking reactions, but in most plants
their physiological roles are not known. To better understand the importance of PPOs in the plant kingdom, we
surveyed PPO gene families in 25 sequenced genomes from chlorophytes, bryophytes, lycophytes, and flowering
plants. The PPO genes were then analyzed in silico for gene structure, phylogenetic relationships, and targeting
signals.
Results: Many previously uncharacterized PPO genes were uncovered. The moss, Physcomitrella patens, contained
13 PPO genes and Selaginella moellendorffii (spike moss) and Glycine max (soybean) each had 11 genes. Populus
trichocarpa (poplar) contained a highly diversified gene family with 11 PPO genes, but several flowering plants had
only a single PPO gene. By contrast, no PPO-like sequences were identified in several chlorophyte (green algae)
genomes or Arabidopsis (A. lyrata and A. thaliana). We found that many PPOs contained one or two introns often
near the 3’ terminus. Furthermore, N-terminal amino acid sequence analysis using ChloroP and TargetP 1.1
predicted that several putative PPOs are synthesized via the secretory pathway, a unique finding as most PPOs are
predicted to be chloroplast proteins. Phylogenetic reconstruction of these sequences revealed that large PPO gene
repertoires in some species are mostly a consequence of independent bursts of gene duplication, while the lineage
leading to Arabidopsis must have lost all PPO genes.
Conclusion: Our survey identified PPOs in gene families of varying sizes in all land plants except in the genus
Arabidopsis. While we found variation in intron numbers and positions, overall PPO gene structure is congruent
with the phylogenetic relationships based on primary sequence data. The dynamic nature of this gene family
differentiates PPO from other oxidative enzymes, and is consistent with a protein important for a diversity of
functions relating to environmental adaptation.
Description
BioMed Central
Keywords
Citation
Tran et al.: The polyphenol oxidase gene family in land plants: Lineage-specific duplication and expansion. BMC Genomics 2012 13:395.