The polyphenol oxidase gene family in poplar: phylogeny, differential expression and identification of a novel, vacuolar isoform

Abstract

Polyphenol oxidases (PPOs) are oxidative enzymes that convert monophenols and o-diphenols to o-quinones using molecular oxygen. The quinone products are highly reactive following tissue damage and can interact with cellular constituents and cause oxidative browning and cross-linking. The induction of PPO in some plants as a result of wounding, herbivore attack, or pathogen infection has implicated them in defense. However, PPO-like enzymes that act as specific hydroxylases, for example in lignan and pigment biosynthesis, have also been discovered. Here, we present the first genome-enabled analysis of a PPO gene family. The Populus trichocarpa genome was found to contain a minimum of nine complete PPO genes, and seven of these were characterized further. The PPO gene family includes both recently duplicated and divergent sequences that are 36-98% identical at the amino acid level. Gene expression profiling in poplar tissues and organs revealed that the PPO genes are all differentially expressed during normal development, but that only a small subset of PPO genes are significantly upregulated by wounding, methyl jasmonate or pathogen infection. Our studies also identified PtrPPO13, a novel PPO gene that is predicted to encode an N-terminal signal peptide. Transient expression of green fluorescent protein fusions demonstrated its localization to the vacuolar lumen. Together, our findings show that the poplar PPO family is diverse and is likely linked to diverse physiological functions.

Chitosan Coating: A Postharvest Treatment to Delay Oxidative Stress in Loquat Fruits during Cold Storage

“…The first enzyme catalyses the oxidation of phenols to quinones that in turn polymerize into undesirable brown pigments. PPO activity increases when cells are damaged, intracellular compartmentation is disrupted and phenolic substrates are released from vacuoles [32]. POD oxidises several antioxidant compounds in the Figure 1.…”

Genome-Wide Analysis of Polyphenol Oxidase Genes and Their Transcriptional Patterns during Grain Development in Sorghum

“…In the majority of the plant species examined so far, there usually exists a family of PPO genes. Furthermore, as demonstrated by recent studies in bread wheat, eggplant, and poplar (Beecher and Skinner 2011;Shetty et al 2011;Tran and Constabel 2011), PPO members in the same plant species often differ in their spatial and temporal expression profiles in different vegetative and reproductive tissues and in response to different environmental cues. At the primary structural level, the plant PPO proteins investigated thus far all possess a signal peptide, an N-terminal domain, a predicted C-terminal domain, and a putative linker region between the N-and C-terminal regions (Marusek et al 2006).…”

“…Using a similar strategy, the PPO gene sequences in rice were found in the website database http:// rice.plantbiology.msu.edu/, and those in tomato were identified in http://mips.helmholtz-muenchen.de/plant/tomato/index .jsp. The deduced PPO proteins were each examined for the presence of an intact binuclear copper center (the CuA and CuB motifs and conserved histidine residues in the two motifs), the tyrosine motif and its interacting residues, and the putative thylakoid transfer domain as detailed previously (Marusek et al 2006;Tran and Constabel 2011). For SbPPO1 and SbPPO8 identified in BTx623, in which no clear thylakoid transfer domain was identified, their deduced protein sequences were subject to signal peptide prediction using the softwares SignalP-4.0 (http://www.cbs.dtu.dk/services/SignalP/; Petersen et al 2011) and Signal-3L (http://www.csbio.sjtu.edu.cn/bioinf/Signal-3L/; Shen and Chou 2007).…”

“…The brown discoloration caused by PPO activity has important influences on the appearance and processing qualities of many crop products (Dicko et al 2006a;Mayer 2006;Queiroz et al 2008). For example, high PPO activity in wheat grains can result in brown or dark discoloration of flour and seriously decreases its quality for noodle making (Anderson and Morris 2001;He et al 2010 To date, genes encoding PPO isozymes have been isolated from a variety of monocotyledonous and dicotyledonous plant species (reviewed in Aniszewski et al 2008;Taketa et al 2010;Shetty et al 2011;Tran and Constabel 2011). In the majority of the plant species examined so far, there usually exists a family of PPO genes.…”

“…At the primary structural level, the plant PPO proteins investigated thus far all possess a signal peptide, an N-terminal domain, a predicted C-terminal domain, and a putative linker region between the N-and C-terminal regions (Marusek et al 2006). The signal peptide targets PPOs to either the thylakoid luminal compartment of chloroplast or the vacuolar lumen (Marusek et al 2006;Tran and Constabel 2011). The N-terminal domain contains the elements required for copper binding and substrate catalysis (i.e., CuA and CuB motifs) and structural maintenance (e.g., the tyrosine motif and its interacting residues) and is thus fairly conserved among plant PPOs; by contrast, the size and structure of the linker region and C-terminal domain are more variable among different PPOs (Marusek et al 2006).…”