Ascorbate peroxidase‐related (APx‐R) is a new heme‐containing protein functionally associated with ascorbate peroxidase but evolutionarily divergent

Abstract

Summary• Peroxidases are involved in several important processes, such as development and responses to environmental cues. In higher plants, most peroxidases are encoded by large, multigenic families that mainly originated from gene and chromosomal duplications.• Using phylogenetic, genomic and functional analyses, we have identified and characterized a new class of putative heme peroxidases, called ascorbate peroxidase-related (APx-R), which arose specifically in the lineage of plants.• The APx-R protein is structurally related to the ascorbate peroxidases, although the active site contains many conserved substitutions. Unlike all other plant peroxidases, which are encoded by gene families, APx-R is encoded by a single-copy gene in virtually all the species analyzed. APx-R proteins are targeted to the chloroplast and can physically interact with chloroplastic APx proteins. APx-Rknockdown rice (Oryza sativa) plants presented delayed development and a disturbed steady state of the antioxidant system compared with wild type. Moreover, the accumulation of APx-R transcripts was modulated by drought, UV irradiation, cold, and aluminum exposure in rice, suggesting the involvement of APx-R in the environmental stress response.• Our results reveal the existence of a new class of heme peroxidase which seems to play a role in the antioxidant system in plants, probably by modulating the activity of chloroplastic APx proteins.

Role of L-ascorbate in alleviating abiotic stresses in crop plants

“…Whereas, in rice, the APX gene family consists of eight genes encoding two cytosolic, two peroxisomal, and three chloroplastic isoforms and one is targeted to the mitochondria (Teixeira et al 2004,2006; Hong et al 2007). Recently, Lazzarotto et al (2011), characterized a new class of rice putative heme peroxidases, APX-R (APX-related), a dually localized protein, targeted to both chloroplasts and mitochondria, which is functionally associated with APX. APX genes have been partially characterized in some plant species such as spinach (Ishikawa et al 1995,1996,1998), cowpea (D’Arcy-Lameta et al 2006) and eggplant (Lin et al 2007).…”

Ascorbate peroxidase-related (APx-R) is not a duplicable gene

“…Noteworthy, this new class does not seem to be subjected to functional duplication. 3 Exhaustive datamining of multiple sequence resources have been performed with available genome and EST libraries to confirm the previous observations. No functional APx-R gene duplication has been detected.…”

A Strategy for Genome-Wide Identification of Gene Based Polymorphisms in Rice Reveals Non-Synonymous Variation and Functional Genotypic Markers

“…Amongst the gene families of interest are the MADS-box family (71 SNPs) that functions in flower and fruit development [35], the protein disulfide isomerase superfamily (22 SNPs) controls diverse metabolic functions including disulfide bond formation and isomerisation during protein folding [36], [37], ascorbate peroxidase (APx) family (19 SNPs) for development and response to environmental cues [38], [39], mitogen-activated protein kinases (MAPKs) and MAPK kinases (MAPKKs) with 19 SNPs that play an important role in response to pathogens and disease resistance cascades, topoisomerase 6 homologs (17 SNPs) involved in overexpression of stress tolerance genes [37]and serine proteases (15 SNPs) known for proteolytic enzymes associated with several essential physiological pathways [40]. The other 15 gene families have single digit SNPs and the rest 11 are conserved (Table 3).…”