Structural diversity and transcription of class III peroxidases from Arabidopsis thaliana

Abstract

Understanding peroxidase function in plants is complicated by the lack of substrate specificity, the high number of genes, their diversity in structure and our limited knowledge of peroxidase gene transcription and translation. In the present study we sequenced expressed sequence tags (ESTs) encoding novel heme-containing class III peroxidases from Arabidopsis thaliana and annotated 73 full-length genes identified in the genome. In total, transcripts of 58 of these genes have now been observed. The expression of individual peroxidase genes was assessed in organ-specific EST libraries and compared to the expression of 33 peroxidase genes which we analyzed in whole plants 3, 6, 15, 35 and 59 days after sowing. Expression was assessed in root, rosette leaf, stem, cauline leaf, flower bud and cell culture tissues using the gene-specific and highly sensitive reverse transcriptasepolymerase chain reaction (RT-PCR).We predicted that 71 genes could yield stable proteins folded similarly to horseradish peroxidase (HRP). The putative mature peroxidases derived from these genes showed 28-94% amino acid sequence identity and were all targeted to the endoplasmic reticulum by N-terminal signal peptides. In 20 peroxidases these signal peptides were followed by various N-terminal extensions of unknown function which are not present in HRP. Ten peroxidases showed a C-terminal extension indicating vacuolar targeting. We found that the majority of peroxidase genes were expressed in root. In total, class III peroxidases accounted for an impressive 2.2% of root ESTs. Rather few peroxidases showed organ specificity. Most importantly, genes expressed constitutively in all organs and genes with a preference for root represented structurally diverse peroxidases (< 70% sequence identity). Furthermore, genes appearing in tandem showed distinct expression profiles. The alignment of 73 Arabidopsis peroxidase sequences provides an easy access to the identification of orthologous peroxidases in other plant species and will provide a common platform for combining knowledge of peroxidase structure and function relationships obtained in various species.

PeroxiBase: A class III plant peroxidase database

“…The homology between paralogs in a plant ranges from 30% to 100%, but very close orthologs exist, even between evolutionarily distant plants. All plant peroxidases contain invariant amino acids essential for their catalytic properties and for their proper folding (Welinder et al, 2002 proteins, like peroxidases from prokaryotes, fungi. The key amino acids that interact with heme are also found in hemoglobins and cytochromes.…”

Isolation of a gene encoding for a class III peroxidase in female flower of Corylus avellana L.

“…2). In fact, it is known that protein structure, amino acid residues and protein size are conserved in all class III peroxidases [5,35]. CavPrx showed a "three intron" structure that is a common feature of the most of class III peroxidases in rice and Arabidopsis [2,7].…”

“…This is the first class III peroxidase isolated in C. avellana and Real Time analysis showed that it is expressed in the styles, with a peak of expression in mature styles; in addition its level of expression increased significantly in styles pollinated with compatible pollen. Despite most of plant peroxidases are active in all part of the plant [5,7] some example of localized peroxidases in particular tissue/organ exist in literature, as reported in the introduction. In particular, five peroxidases were identified to be expressed in particular parts of the flower: GhPrx37 in G. hirsutum resulted expressed only in stamen and pollen [12]; SsqPrx01 in S. squalidus was demonstrated to be localized in the stigmatic papillae and expressed only in stigmas with maximal level at anthesis [6]; AtPrx28, AtPrx39 and AtPrx58 in A. thaliana resulted expressed in stigmas [13,14].…”

“…Delannoy et al [38] carried out a molecular analysis on 12 peroxidases of cotton and, after phylogenetical analysis, four peroxidases (including GhPrx10) with the same expression profile resulted dispersed in the dendrogram. On the other hand an extensive study on Arabidopsis peroxidases showed that very similar genes have not similar biological role or expression pattern [5,8]. This could be due to translational regulations, which peroxidases are subjected to, for regulating the amount of protein in a particular tissue/organ and so its activity [8,39].…”

“…Other amino acid residues that are considered of importance for the integrity of protein structure were present (Fig. 2) [5]. All these characteristics are common to most class III peroxidases.…”