Disease relevance of APX1

• A cDNA clone encoding ascorbate peroxidase (AP, EC 1.11.1.11) was isolated from a phage lambda gt11 library of cDNA from Arabidopsis thaliana by immunoscreening with monoclonal antibodies against the enzyme, and then sequenced [1].
• The functional roles of modulations of APX expression and the interdependence of heat stress and oxidative stress response and signaling mechanisms are discussed [2].
• The hypersensitivity of some of the vtc mutants to ozone and UV-B radiation, the rapid response of ascorbate peroxidase expression to (photo)-oxidative stress, and the properties of transgenic plants with altered ascorbate peroxidase activity all support an important antioxidative role for ascorbate [3].

High impact information on APX1

• Overproduction of both ACD2 (localized to mitochondria and chloroplasts) and ascorbate peroxidase (localized to chloroplasts) greatly reduces P. syringae-induced PCD, suggesting a pro-PCD role for mitochondrial and chloroplast events [4].
• Our study points to a key role for the cytosol in protecting the chloroplast during light stress and provides evidence for cross-compartment protection of thylakoid and stromal/mitochondrial APXs by cytosolic APX1 [5].
• This signal, which preceded the photooxidative burst of hydrogen peroxide (H2O2) associated with photoinhibition of photosynthesis, resulted in a rapid increase (within 15 min) in mRNA levels of two cytosolic ascorbate peroxidase genes (APX1 and APX2) [6].
• Photosynthetic electron transport regulates the expression of cytosolic ascorbate peroxidase genes in Arabidopsis during excess light stress [6].
• We have addressed this problem by modulating noninvasively the level of H(2)O(2) in plastids by means of a transgenic line that overexpresses the thylakoid-bound ascorbate peroxidase (tAPX) [7].

Biological context of APX1

• Nucleotide sequence and primer extension analyses of this gene (APX1) revealed nine exons split by eight introns, one of which is inserted in the 5'-untranslated region [8].
• Amino acid residues at the active site of yeast cytochrome c peroxidase are conserved in the amino acid sequence of Arabidopsis AP [1].
• The predicted amino acid sequence of the mature AP of A. thaliana, deduced from the nucleotide sequence, consists of 249 amino acid residues, which is 34% homologous with cytochrome c peroxidase of yeast, but less homologous with other plant peroxidases [1].
• Exposure of plants to 0.1 ppm ozone enhanced the APX1 mRNA level within 3 h, which showed a diurnal rhythm similar to that of the control [9].
• These results demonstrate that near-ambient concentrations of ozone as well as similar concentrations of sulfur dioxide can induce APX1 gene expression in A. thaliana [9].

Anatomical context of APX1

• Our data suggest that Apx2 is a novel heat shock gene and that the enzymatic activity of APX2/APX(S) is required to compensate heat stress-dependent decline of APX1 activity in the cytosol [2].
• The H2O2 byproduct of fatty acid catabolism in plant peroxisomes is removed in part by a membrane-associated antioxidant system that involves both an ascorbate peroxidase and a monodehydroascorbate reductase (MDAR) [10].
• Previously we reported (R.T. Mullen, C.S. Lisenbee, J.A. Miernyk, R.N. Trelease [1999] Plant Cell 11: 2167-2185) that overexpressed ascorbate peroxidase (APX), a peroxisomal membrane protein, sorted indirectly to Bright Yellow-2 cell peroxisomes via a subdomain of the endoplasmic reticulum (ER; peroxisomal endoplasmic reticulum [pER]) [11].
• Peroxisomal ascorbate peroxidase resides within a subdomain of rough endoplasmic reticulum in wild-type Arabidopsis cells [11].
• Pumpkin peroxisomal ascorbate peroxidase is localized on peroxisomal membranes and unknown membranous structures [12].

Associations of APX1 with chemical compounds

• The exon/intron organization of the APX1 gene differs from that of the guaiacol peroxidase genes [8].
• By using in vivo dimethyl sulfate footprinting, we showed that proteins interacted with a G/C-rich element found in the apx1 promoter [13].
• From sequence analysis of three novel ascorbate peroxidases from Arabidopsis thaliana to structure, function and evolution of seven types of ascorbate peroxidase [14].
• By employing tDNA insertion mutants of A. thaliana lacking expression of AtprxII F (KO-AtPrxII F), it is shown that under optimal environmental conditions the absence of PrxII F is almost fully compensated for, possibly by increases in activity of mitochondrial ascorbate peroxidase and glutathione-dependent peroxidase [15].
• UV-B exposure preferentially enhanced guaiacol-peroxidases, ascorbate peroxidase, and peroxidases specific to coniferyl alcohol and modified the substrate affinity of ascorbate peroxidase [16].

Physical interactions of APX1

• The Arabidopsis gene APX3 that encodes a putative peroxisomal membrane-bound ascorbate peroxidase was expressed in transgenic tobacco plants [17].

Other interactions of APX1

• In this study, the localization of a putative peroxisomal membrane-bound ascorbate peroxidase, APX3 from Arabidopsis, was confirmed by studying the green fluorescent protein (GFP)-APX3 fusion protein in transgenic plants [18].
• This direct sorting of PMP22 to peroxisomes contrasts with the indirect sorting reported previously for cottonseed (Gossypium hirsutum) ascorbate peroxidase, an integral PMP that sorts to peroxisomes via a subdomain of the endoplasmic reticulum [19].
• The zinc finger protein Zat12 is required for cytosolic ascorbate peroxidase 1 expression during oxidative stress in Arabidopsis [20].
• The activities of thylakoid and stromal ascorbate peroxidase and particularly monodehydroascorbate reductase were increased as were transcripts for these enzymes [21].
• Heat stress- and heat shock transcription factor-dependent expression and activity of ascorbate peroxidase in Arabidopsis [2].

References