Developmental, hormone- and stress-modulated expression profiles of four members of the Arabidopsis copper-amine oxidase gene family

Copper-containing amine oxidases (CuAOs) catalyze polyamines (PAs) terminal oxidation producing ammonium, an aminoaldehyde and hydrogen peroxide (H2O2). Plant CuAOs are induced by stress-related hormones, methyl-jasmonate (MeJA), abscisic acid (ABA) and salicylic acid (SA). In the Arabidopsis genome, eight genes encoding CuAOs have been identified. Here, a comprehensive investigation of the expression pattern of four genes encoding AtCuAOs from the α and γ phylogenetic subfamilies, the two peroxisomal AtCuAOα2 (At1g31690) and AtCuAOα3 (At1g31710) and the two apoplastic AtCuAOγ1 (At1g62810) and AtCuAOγ2 (At3g43670), has been carried out by RT-qPCR and promoter::green fluorescent protein-β-glucuronidase fusion (GFP-GUS). Expression in hydathodes of new emerging leaves (AtCuAOγ1 and AtCuAOγ2) and/or cotyledons (AtCuAOα2, AtCuAOγ1 and AtCuAOγ2) as well as in vascular tissues of new emerging leaves and in cortical root cells at the division/elongation transition zone (AtCuAOγ1), columella cells (AtCuAOγ2) or hypocotyl and root (AtCuAOα3) was identified. Quantitative and tissue-specific gene expression analysis performed by RT-qPCR and GUS-staining in 5- and 7-day-old seedlings under stress conditions or after treatments with hormones or PAs, revealed that all four AtCuAOs were induced during dehydration recovery, wounding, treatment with indoleacetic acid (IAA) and putrescine (Put). AtCuAOα2, AtCuAOα3, AtCuAOγ1 and AtCuAOγ2 expression in vascular tissues and hydathodes involved in water supply and/or loss, along with a dehydration-recovery dependent gene expression, would suggest a role in water balance homeostasis. Moreover, occurrence in zones where an auxin maximum has been observed along with an IAA-induced alteration of expression profiles, support a role in tissue maturation and xylem differentiation events

Mutation of Arabidopsis copper-containing amine oxidase gene AtCuAOδ alters polyamines, reduces gibberellin content and affects development

Polyamines (PAs) are essential metabolites in plants performing multiple functions during growth and development. Copper-containing amine oxidases (CuAOs) catalyse the catabolism of PAs and in Arabidopsis thaliana are encoded by a gene family. Two mutants of one gene family member, AtCuAOδ, showed delayed seed germination, leaf emergence, and flowering time. The height of the primary inflorescence shoot was reduced, and developmental leaf senescence was delayed. Siliques were significantly longer in mutant lines and contained more seeds. The phenotype of AtCuAOδ over-expressors was less affected. Before flowering, there was a significant increase in putrescine in AtCuAOδ mutant leaves compared to wild type (WT), while after flowering both spermidine and spermine concentrations were significantly higher than in WT leaves. The expression of GA (gibberellic acid) biosynthetic genes was repressed and the content of GA1, GA7, GA8, GA9, and GA20 was reduced in the mutants. The inhibitor of copper-containing amine oxidases, aminoguanidine hydrochloride, mimicked the effect of AtCuAOδ mutation on WT seed germination. Delayed germination, reduced shoot height, and delayed flowering in the mutants were rescued by GA3 treatment. These data strongly suggest AtCuAOδ is an important gene regulating PA homeostasis, and that a perturbation of PAs affects plant development through a reduction in GA biosynthesis

Selenoprotein: Potential Player in Redox Regulation in <i>Chlamydomonas reinhardtii</i>

Selenium (Se) is an essential micro-element for many organisms, including Chlamydomonas reinhardtii, and is required in trace amounts. It is obtained from the 21st amino acid selenocysteine (Sec, U), genetically encoded by the UGA codon. Proteins containing Sec are known as selenoproteins. In eukaryotes, selenoproteins are present in animals and algae, whereas fungi and higher plants lack them. The human genome contains 25 selenoproteins, most of which are involved in antioxidant defense activity, redox regulation, and redox signaling. In algae, 42 selenoprotein families were identified using various bioinformatics approaches, out of which C. reinhardtii is known to have 10 selenoprotein genes. However, the role of selenoproteins in Chlamydomonas is yet to be reported. Chlamydomonas selenoproteins contain conserved domains such as CVNVGC and GCUG, in the case of thioredoxin reductase, and CXXU in other selenoproteins. Interestingly, Sec amino acid residue is present in a catalytically active domain in Chlamydomonas selenoproteins, similar to human selenoproteins. Based on catalytical active sites and conserved domains present in Chlamydomonas selenoproteins, we suggest that Chlamydomonas selenoproteins could have a role in redox regulation and defense by acting as antioxidants in various physiological conditions

Plant Copper Amine Oxidases: Key Players in Hormone Signaling Leading to Stress-Induced Phenotypic Plasticity

Polyamines are ubiquitous, low-molecular-weight aliphatic compounds, present in living organisms and essential for cell growth and differentiation. Copper amine oxidases (CuAOs) oxidize polyamines to aminoaldehydes releasing ammonium and hydrogen peroxide, which participates in the complex network of reactive oxygen species acting as signaling molecules involved in responses to biotic and abiotic stresses. CuAOs have been identified and characterized in different plant species, but the most extensive study on a CuAO gene family has been carried out in Arabidopsis thaliana. Growing attention has been devoted in the last years to the investigation of the CuAO expression pattern during development and in response to an array of stress and stress-related hormones, events in which recent studies have highlighted CuAOs to play a key role by modulation of a multilevel phenotypic plasticity expression. In this review, the attention will be focused on the involvement of different AtCuAOs in the IAA/JA/ABA signal transduction pathways which mediate stress-induced phenotypic plasticity events

The Copper Amine Oxidase AtCuAOδ Participates in Abscisic Acid-Induced Stomatal Closure in Arabidopsis

Plant copper amine oxidases (CuAOs) are involved in wound healing, defense against pathogens, methyl-jasmonate-induced protoxylem differentiation, and abscisic acid (ABA)-induced stomatal closure. In the present study, we investigated the role of the Arabidopsis thaliana CuAO&delta; (AtCuAO&delta;; At4g12290) in the ABA-mediated stomatal closure by genetic and pharmacological approaches. Obtained data show that AtCuAO&delta; is up-regulated by ABA and that two Atcuao&delta; T-DNA insertional mutants are less responsive to this hormone, showing reduced ABA-mediated stomatal closure and H2O2 accumulation in guard cells as compared to the wild-type (WT) plants. Furthermore, CuAO inhibitors, as well as the hydrogen peroxide (H2O2) scavenger N,N1-dimethylthiourea, reversed most of the ABA-induced stomatal closure in WT plants. Consistently, AtCuAO&delta; over-expressing transgenic plants display a constitutively increased stomatal closure and increased H2O2 production compared to WT plants. Our data suggest that AtCuAO&delta; is involved in the H2O2 production related to ABA-induced stomatal closure

The MeJA-inducible copper amine oxidase AtAO1 is expressed in xylem tissue and guard cells

Copper amine oxidases oxidize the polyamine putrescine to 4-amino-and guard cells during acclimation to adverse environmental conditions. butanal with the production of the plantsignal molecule hydrogen peroxide (H2O2) and ammonia. The Arabidopsis (Arabidopsis thaliana) gene At4g14940 (AtAO1, previously referred to as ATAO1) encodes an apoplastic copper amine oxidase expressed in lateral root cap cells and developing xylem, especially in root protoxylem and metaxylem precursors. In our recent study, we demonstrated that AtAO1 expression is strongly induced in the root vascular tissues by the wound-signal hormone methyl jasmonate (MeJA). Furthermore, we also demonstrated that the H2O2 derived by the AtAO1-driven oxidation of putrescine, mediates the MeJA-induced early protoxylem differentiation in Arabidopsis roots. H2O2 may contribute to protoxylem differentiation by signaling developmental cell death and by acting as co-substrate in peroxidase-mediated cell wall stiffening and lignin polymerization. Here, by the means of AtAO1 promoter:: green fluorescent protein-b-glucuronidase (AtAO1::GFP-GUS) fusion analysis, we show that a strong AtAO1 gene expression occurs also in guard cells of leaves and flowers. The high expression levels of AtAO1 in tissues or cell types regulating water supply and water loss may suggest a role of the encoded protein in water balance homeostasis, by modulating coordinated adjustments in anatomical and functional features of xylem tissu

Cell Wall Amine Oxidases: New Players in Root Xylem Differentiation under Stress Conditions

Polyamines (PAs) are aliphatic polycations present in all living organisms. A growing body of evidence reveals their involvement as regulators in a variety of physiological and pathological events. They are oxidatively deaminated by amine oxidases (AOs), including copper amine oxidases (CuAOs) and flavin adenine dinucleotide (FAD)-dependent polyamine oxidases (PAOs). The biologically-active hydrogen peroxide (H2O2) is a shared compound in all of the AO-catalyzed reactions, and it has been reported to play important roles in PA-mediated developmental and stress-induced processes. In particular, the AO-driven H2O2 biosynthesis in the cell wall is well known to be involved in plant wound healing and pathogen attack responses by both triggering peroxidase-mediated wall-stiffening events and signaling modulation of defense gene expression. Extensive investigation by a variety of methodological approaches revealed high levels of expression of cell wall-localized AOs in root xylem tissues and vascular parenchyma of different plant species. Here, the recent progresses in understanding the role of cell wall-localized AOs as mediators of root xylem differentiation during development and/or under stress conditions are reviewed. A number of experimental pieces of evidence supports the involvement of apoplastic H2O2 derived from PA oxidation in xylem tissue maturation under stress-simulated conditions