Skip to main content
PMC home page
Plant Signaling & Behavior logoLink to Plant Signaling & Behavior
. 2010 Aug 1;5(8):1025–1027. doi: 10.4161/psb.5.8.12294

Protein interactors of acyl-CoA-binding protein ACBP2 mediate cadmium tolerance in Arabidopsis

Wei Gao 1, Hong-Ye Li 1,2, Shi Xiao 1, Mee-Len Chye 1,✉
PMCID: PMC3115187  PMID: 20657176

Abstract

In our recent paper in the Plant Journal, we reported that Arabidopsis thaliana lysophospholipase 2 (lysoPL2) binds acyl-CoA-binding protein 2 (ACBP2) to mediate cadmium [Cd(II)] tolerance in transgenic Arabidopsis. ACBP2 contains ankyrin repeats that have been previously shown to mediate protein-protein interactions with an ethylene-responsive element binding protein (AtEBP) and a farnesylated protein 6 (AtFP6). Transgenic Arabidopsis ACBP2-overexpressors, lysoPL2-overexpressors and AtFP6-overexpressors all display enhanced Cd(II) tolerance, in comparison to wild type, suggesting that ACBP2 and its protein partners work together to mediate Cd(II) tolerance. Given that recombinant ACBP2 and AtFP6 can independently bind Cd(II) in vitro, they may be able to participate in Cd(II) translocation. The binding of recombinant ACBP2 to [14C]linoleoyl-CoA and [14C]linolenoyl-CoA implies its role in phospholipid repair. In conclusion, ACBP2 can mediate tolerance to Cd(II)-induced oxidative stress by interacting with two protein partners, AtFP6 and lysoPL2. Observations that ACBP2 also binds lysophosphatidylcholine (lysoPC) in vitro and that recombinant lysoPL2 degrades lysoPC, further confirm an interactive role for ACBP2 and lysoPL2 in overcoming Cd(II)-induced stress.

Key words: acyl-CoA-binding protein, cadmium, hydrogen peroxide, lysophospholipase, oxidative stress

Acyl-CoA-binding proteins (ACBP1 to ACBP6) are encoded by a multigene family in Arabidopsis thaliana.1 These ACBP proteins are well studied in Arabidopsis in comparison to other organisms,1–4 and are located in various subcellular compartments.1 Plasma membranelocalized ACBP1 and ACBP2 contain ankyrin repeats that have been shown to function in protein-protein interactions.5,6 ACBP1 and ACBP2 which share 76.9% amino acid identity also confer tolerance in transgenic Arabidopsis to lead [Pb(II)] and Cd(II), respectively.1,5,7 Since recombinant ACBP1 and ACBP2 bind linolenoyl-CoA and linoleoyl-CoA in vitro, they may possibly be involved in phospholipid repair in response to heavy metal stress at the plasma membrane.5,7 In contrast, ACBP3 is an extracellularly-localized protein8 while ACBP4, ACBP5 and ACBP6 are localized to cytosol.9,10 ACBP1 and ACBP6 have recently been shown to be involved in freezing stress.9,11 ACBP4 and ACBP5 bind oleoyl-CoA ester and their mRNA expressions are lightregulated.12,13 Besides acyl-CoA esters, some ACBPs also bind phospholipids.9,11,13 To investigate the biological function of ACBP2, we have proceeded to establish its interactors at the ankyrin repeats, including AtFP6,5 AtEBP6 and now lysoPL2 in the Plant Journal paper. While the significance in the interaction of ACBP2 with AtEBP awaits further investigations, some parallels can be drawn between those of ACBP2 with AtFP6 and with lysoPL2.

AtFP6 and lysoPL2 are Protein Partners of ACBP2 in Mediating Cd(II) Tolerance

Similar to lysoPL2, the heavy-metal-binding protein AtFP6 was first identified to interact with ACBP2 in yeast two-hybrid analysis.5 Subsequently, Arabidopsis AtFP6-overexpressors demonstrated improved Cd(II) tolerance in comparison to wild type.5 AtFP6 belongs to the AtFP family of proteins that posses an M/LXCXXC domain participating in heavy metal binding.5 The AtFP6 mRNA is Cd(II)-inducible in Arabidopsis roots, in vitro translated AtFP6 was observed to bind Pb(II), Cd(II) and copper [Cu(II)], and (His)6-AtFP6 binds Pb(II).5 Hence, AtFP6 may possibly mediate Pb(II), Cd(II) and Cu(II) transport in Arabidopsis roots.5 Given that (His)6-ACBP2 binds [14C]linoleoyl-CoA and [14C]linolenoyl-CoA, the precursors for phospholipid repair following lipid peroxidation from heavy metal stress at the plasma membrane, and that ACBP2-overexpressors are more tolerant to H2O2 than wild type, a role for ACBP2 in poststress membrane repair has been previously proposed.5

We identified another interactor of ACBP2 that resembles AtFP6 in its ability to confer tolerance to Cd(II) when overexpressed in transgenic Arabidopsis. This other ACBP2 protein interactor, Arabidopsis lysophospholipase lysoPL2, showed 33% to 37% amino acid identity to Arabidopsis lysoPL1 (At2g39400) and five lysoPL1-like proteins by BLASTP analysis. Lysophospholipases are enzymes that catalyze the degradation of lysophospholipids to produce fatty acids and glycerolphosphate derivatives.14 They are well-characterized in mammals and bacteria15,16 but few plant lysophospholipases have been reported.17,18 Although the expression of Arabidopsis lysophospholipase 1 (lysoPL1) has been demonstrated to be induced by pathogen treatment,18 its in vivo biological functions as well as those of other plant lysophospholipases remain to be elucidated. In our recent study, we have demonstrated that lysoPL2 and ACBP2 function together to promote degradation of lysoPC in response to Cd(II)-induced oxidative stress.

ACBP2 Interactors (AtEBP, AtFP6 and lysoPL2) are Stress-Inducible

All three protein interactors of ACBP2, so far identified, are encoded by stress-inducible genes. AtEBP mRNA is induced by ethylene and pathogen19 while the mRNA of AtFP6 is Cd(II)- and zinc [Zn(II)]-inducible.5 The mRNA of lysoPL2 has been shown to be Zn(II)- and H2O2-inducible and its protein, Cd(II)- and Zn(II)-inducible. Both AtFP6,5 and lysoPL2 displayed spatial expression patterns that overlap that of ACBP2, with higher expression in root, stem and flower and lower expression in silique and leaf. However AtEBP showed a slightly different expression pattern with higher mRNA accumulation in leaf and stem.19 By using an ACBP2 derivative lacking the ankyrin repeat, we have shown that all three protein partners interact at the ankyrin repeats of ACBP2.5,6 Although the significance in the interaction of AtEBP with ACBP2 is currently less clear, both AtFP6 and lysoPL2 have emerged to work with ACBP2 in mediating Cd(II) tolerance.

Conclusions and Perspectives

Many proteins including P1B-type heavy metal ATPases, ABC transporter, phytochelatins, methallothioneins and oxidative stress-related proteins have been associated with heavy metal stress.20–23 AtHMA4, a P1B-type heavy metal ATPase, translocates Zn(II) and Cd(II) from root to shoot.20 AtOXS3, an oxidative stress-related protein, confers tolerance to Cd(II) and oxidizing chemicals.22 Phytochelatins and methallothioneins bind Cd(II) to form complexes.23 Our recent findings present a mechanism involving lysoPL2 recruitment by ACBP2 to remove toxic lysoPC. This promotes repair of peroxidized phospholipids arising from Cd(II)-induced oxidative stress at the plasma membrane.

Heavy metals including Cu(II), iron [Fe(III)], nickel [Ni(II)], Cd(II) and Zn(II) are known to induce oxidative stress at high concentrations.24–27 Cu(II) and Fe(III) belong to transition metals that induce lipid peroxidation and oxidative stress via Fenton-type reactions.24 Cd(II) and Zn(II) are not transition metals, however they can also activate reactive oxygen species to induce lipid peroxidation.25–27 Since lysoPL2 has been shown to confer tolerance to Cd(II)-induced oxidative stress, it will be worthwhile to investigate if it could also be used in protection against a wider range of metals in future studies.

Acknowledgements

This work was supported by the University Grants Committee of the Hong Kong Special Administrative Region, China (Project AoE/B-07/99) and University of Hong Kong (Grant 10208034, studentship to W.G. and postdoctoral fellowship to S.X.).

Addendum to: Gao W, Li HY, Xiao S, Chye ML. Acyl-CoA-binding protein 2 binds lysophospholipase 2 and lysoPC to promote tolerance to cadmium-induced oxidative stress in transgenic Arabidopsis. Plant J. 2010;62:989–1003. doi: 10.1111/j.1365-313X.2010.04209.x.

Footnotes

References

  • 1.Xiao S, Chye ML. An Arabidopsis family of six acyl-CoA-binding proteins has three cytosolic members. Plant Physiol Biochem. 2009;47:479–484. doi: 10.1016/j.plaphy.2008.12.002. [DOI] [PubMed] [Google Scholar]
  • 2.Guerrero C, Martín-Rufián M, Reina JJ, Heredia A. Isolation and characterization of a cDNA encoding a membrane bound acyl-CoA-binding protein from Agave americana L. epidermis. Plant Physiol Biochem. 2006;44:85–90. doi: 10.1016/j.plaphy.2006.01.002. [DOI] [PubMed] [Google Scholar]
  • 3.Larsen MK, Tuck S, Faergeman NJ, Knudsen J. MAA-1, a novel acyl-CoA-binding protein involved in endosomal vesicle transport in Caenorhabditis elegans. Mol Biol Cell. 2006;17:4318–4329. doi: 10.1091/mbc.E06-01-0035. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Zeng B, Cai X, Zhu G. Functional characterization of a fatty acyl-CoA-binding protein (ACBP) from the apicomplexan Cryptosporidium parvum. Microbiology. 2006;152:2355–2363. doi: 10.1099/mic.0.28944-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5.Gao W, Xiao S, Li HY, Tsao SW, Chye ML. Arabidopsis thaliana acyl-CoA-binding protein ACBP2 interacts with a heavy-metal-binding protein AtFP6. New Phytol. 2009;181:89–102. doi: 10.1111/j.1469-8137.2008.02631.x. [DOI] [PubMed] [Google Scholar]
  • 6.Li HY, Chye ML. Arabidopsis acyl-CoA binding protein ACBP2 interacts with an ethylene-responsive element binding protein AtEBP via its ankyrin repeats. Plant Mol Biol. 2004;54:233–243. doi: 10.1023/B:PLAN.0000028790.75090.ab. [DOI] [PubMed] [Google Scholar]
  • 7.Xiao S, Gao W, Chen QF, Ramalingam S, Chye ML. Overexpression of membrane-associated acyl-CoA-binding protein ACBP1 enhances lead tolerance in Arabidopsis. Plant J. 2008;54:141–151. doi: 10.1111/j.1365-313X.2008.03402.x. [DOI] [PubMed] [Google Scholar]
  • 8.Leung KC, Li HY, Xiao S, Tse MH, Chye ML. Arabidopsis ACBP3 is an extracellularly targeted acyl-CoA-binding protein. Planta. 2006;223:871–881. doi: 10.1007/s00425-005-0139-2. [DOI] [PubMed] [Google Scholar]
  • 9.Chen QF, Xiao S, Chye ML. Overexpression of the Arabidopsis 10-kilodalton acyl-CoA-binding protein ACBP6 enhances freezing tolerance. Plant Physiol. 2008;148:304–315. doi: 10.1104/pp.108.123331. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Xiao S, Li HY, Zhang JP, Chan SW, Chye ML. Arabidopsis acyl-CoA-binding proteins ACBP4 and ACBP5 are subcellularly localized to the cytosol and ACBP4 depletion affects membrane lipid composition. Plant Mol Biol. 2008;68:571–583. doi: 10.1007/s11103-008-9392-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Du ZY, Xiao S, Chen QF, Chye ML. Depletion of the membrane-associated acyl-coenzyme A-binding protein ACBP1 enhances the ability of cold acclimation in Arabidopsis. Plant Physiol. 2010;152:1585–1597. doi: 10.1104/pp.109.147066. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Leung KC, Li HY, Mishra G, Chye ML. ACBP4 and ACBP5, novel Arabidopsis acyl-CoA-binding proteins with kelch motifs that bind oleoyl-CoA. Plant Mol Biol. 2004;55:297–309. doi: 10.1007/s11103-004-0642-z. [DOI] [PubMed] [Google Scholar]
  • 13.Xiao S, Chen QF, Chye ML. Light-regulated Arabidopsis ACBP4 and ACBP5 encode cytosolic acyl-CoA-binding proteins that bind phosphatidylcholine and oleoyl-CoA ester. Plant Physiol Biochem. 2009;47:926–933. doi: 10.1016/j.plaphy.2009.06.007. [DOI] [PubMed] [Google Scholar]
  • 14.Wang A, Dennis EA. Mammalian lysophospholipases. Biochim Biophys Acta. 1999;1439:1–16. doi: 10.1016/s1388-1981(99)00063-3. [DOI] [PubMed] [Google Scholar]
  • 15.Doi O, Nojima S. Lysophospholipase of Escherichia coli. J Biol Chem. 1975;250:5208–5214. [PubMed] [Google Scholar]
  • 16.Toyoda T, Sugimoto H, Yamashita S. Sequence, expression in Escherichia coli, and characterization of lysophospholipase II. Biochim Biophys Acta. 1999;1437:182–193. doi: 10.1016/s1388-1981(99)00007-4. [DOI] [PubMed] [Google Scholar]
  • 17.Fujikura Y, Baisted D. Purification and characterization of a basic lysophospholipase in germinating barley. Arch Biochem Biophys. 1985;243:570–578. doi: 10.1016/0003-9861(85)90534-x. [DOI] [PubMed] [Google Scholar]
  • 18.de Torres Zabela M, Fernandez-Delmond I, Niittyla T, Sanchez P, Grant M. Differential expression of genes encoding Arabidopsis phospholipases after challenge with virulent or avirulent Pseudomonas isolates. Mol Plant Microbe Interact. 2002;15:808–816. doi: 10.1094/MPMI.2002.15.8.808. [DOI] [PubMed] [Google Scholar]
  • 19.Li HY, Xiao S, Chye ML. Ethylene- and pathogen-inducible Arabidopsis acyl-CoA-binding protein 4 interacts with an ethylene-responsive element binding protein. J Exp Bot. 2008;59:3997–4006. doi: 10.1093/jxb/ern241. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Verret F, Gravot A, Auroy P, Leonhardt N, David P, Nussaume L, et al. Overexpression of AtHMA4 enhances root-to-shoot translocation of zinc and cadmium and plant metal tolerance. FEBS Lett. 2004;576:306–312. doi: 10.1016/j.febslet.2004.09.023. [DOI] [PubMed] [Google Scholar]
  • 21.Kim DY, Bovet L, Maeshima M, Martinoia E, Lee Y. The ABC transporter AtPDR8 is a cadmium extrusion pump conferring heavy metal resistance. Plant J. 2007;50:207–218. doi: 10.1111/j.1365-313X.2007.03044.x. [DOI] [PubMed] [Google Scholar]
  • 22.Blanvillain R, Kim JH, Wu S, Lima A, Ow DW. OXIDATIVE STRESS 3 is a chromatin-associated factor involved in tolerance to heavy metals and oxidative stress. Plant J. 2009;57:654–665. doi: 10.1111/j.1365-313X.2008.03717.x. [DOI] [PubMed] [Google Scholar]
  • 23.Cobbett CS. Phytochelatins and their roles in heavy metal detoxification. Plant Physiol. 2000;123:825–832. doi: 10.1104/pp.123.3.825. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Stohs SJ, Bagchi D. Oxidative mechanisms in the toxicity of metal ions. Free Radic Biol Med. 1995;18:321–336. doi: 10.1016/0891-5849(94)00159-h. [DOI] [PubMed] [Google Scholar]
  • 25.Madhava Rao KV, Sresty TVS. Antioxidative parameters in the seedlings of pigeonpea (Cajanus cajan (L.) Millspaugh) in response to Zn and Ni stresses. Plant Sci. 2000;157:113–128. doi: 10.1016/s0168-9452(00)00273-9. [DOI] [PubMed] [Google Scholar]
  • 26.Schützendübel A, Polle A. Plant responses to abiotic stresses: heavy metal-induced oxidative stress and protection by mycorrhization. J Exp Bot. 2002;53:1351–1365. [PubMed] [Google Scholar]
  • 27.Jin XF, Yang XE, Islam E, Liu D, Mahmood Q, Li H, Li J. Ultrastructural changes, zinc hyperaccumulation and its relation with antioxidants in two ecotypes of Sedum alfredii Hance. Plant Physiol Biochem. 2008;46:997–1006. doi: 10.1016/j.plaphy.2008.06.012. [DOI] [PubMed] [Google Scholar]

Articles from Plant Signaling & Behavior are provided here courtesy of Taylor & Francis

RESOURCES