Microalgae are predominantly aquatic organisms that must be able to discriminate between essential and non-essential heavy metal ions. In addition, they must maintain non-toxic concentrations of these ions inside their cells. In this way, two principal mechanisms have been identified, one which prevents the indiscriminate entrance of heavy metal ions into the cell (i.e., exclusion) and the other which prevents bioavailability of these toxic ions once inside the cell (i.e., the formation of complexes). The molecules responsible for the first mechanism are extra-cellular polymers, mainly carbohydrates; those responsible for the second are essentially the two type metal-chelating peptides: enzymatically synthesized phytochelatins (PCs- class III metallothioneins -MtIII), and gene-encoded metallothioneins (MTs) (1). MTs are low molecular weight, cysteine-rich metal chelators with an ability to bind heavy metal ions through metal-thiolate bonds. In addition, the thiol(ate)s in MTs can act as powerful antioxidants, and hence MTs may have roles in protection against oxidative stress (2). Mts are widely distributed in animals, plants, fungi as well as cyanobacteria. Plant MTs (pMTs) are considerably longer than their animal counterparts owing to the exclusive presence of a 30-50 residue-long, Cys-devoid region, between the N- and C-terminal Cys-rich domains (four to eight Cys each). Specifically, the distribution of the Cys residues and the length of the spacer region have been used to further classify plant MTs into four subtypes (3, 4). Currently, pMTs have been extensively identified as a multigenic family in angiosperms (A. thaliana as a model) (3), in gymnosperms (5) and in macroalgae (Fucus) (6), constituting family 15 of the global MTs Kägi classification (7). To date, no evidences of genes encoding Mts in microalgae are reported, although the induction of cadmium-binding MT-like protein has been found in the unicellular algae Chlamidomonas sorokiniana (8) and Chlamidomonas vulgaris (9). In this work we reported the first evidence of a Mts gene from the microalga Scenedesmus acutus. In the case of the heavy metal tolerance of S. acutus, previous data report the implication of reduced glutathione (GSH) and Phytochelatins-MtIII as the molecular mechanism underlying the Cd tolerance (10). By RT-PCR amplification approach using degenerate primers, we amplified a full length cDNA of 280 bp sharing high identity with plant metallothioneins. The deduced protein consisted of 91 residues (mol wt of 9,2kDa) which contains 8 Cys residues arranged in CXC and CXXC motifs and showing a high identity homology (89%-98%) with other type2 Mts of the Silene genus. Despite this, the primary structures of Scenedesmus acutus MTs ( named ScaMT) shows some differences with the canonical pMts type 2 which relate it to an archetypal Type 2 sequences from other pMTs members. So, the evidence that ScaMT sequences shows similarity to Types 2 is a phylogenetically important finding and supports both the existence of a common ancestral metallothionein and its diversification at a point after the evolution of Chlorophyta and Streptophyta lineage. Work is in progress in order to define the genomic feature of ScaMT gene and its functional role (response to different heavy metals and/or stress condition). The results will also elucidate the different implications of the two type of heavy metal binding peptides (enzyme and encoding synthesized) in S. acutus in order to better understand the metal tolerance and/or the bioaccumulation mechanisms in this microalga. These molecular mechanism would be potential engineerized to improve the algal phytoremediation performance. 1) H.V. Perales-Vela, J.M. Peña-Castro, R.O. Cañizares-Villanueva (2006) Chemospere, 64, 1-10 2) V. H. Hassinen, A. I. Tervahauta, H. Schat, S.O. Karenlampi (2011) Plant Biol., 13, 225-232 3) C.S. Cobbett, P.B. Goldsbrough (2002) Annu. Rev. Plant Biol., 53, 159-182 4) N.J. Robinson, A.M. Tommey, C. Kuske, P.J. Jackson (1993) Biochem. J., 295, 1-10 5) M. Chatthai, K.H. Kaukinen, T.J. Tranbarger, P.K. Gupta, S. Misra (1997) Plant Mol. Biol. 34, 243-254 6) C.A. Morris, B. Nicolaus, V. Sampson, J.L. Harwood, P. Kille (1999) Biochem. J., 338, 553-560 7) P.A. Binz, J.H.R. Kägi (2001) Metallothionein. http://www. bioc.uzh.ch/mtpage/MT.html 8) N. Yoshida, K. Ishii, T. Okuno, K. Tanaka (2006) Current Microbiology, 52, 460-463 9) Z. Huang, L. Li, G. Huang, Q. Yan, B. Shi, X. Xu (2009) Aquat. Toxicol., 91, 54-61 10) E. Torricelli, G. Gorbi, B. Pawlik-Skowronska, L. Sanità di Toppi, M.G. Corradi (2004) Aquat. Toxicol., 68, 315-323

A putative metallothionein from the microalga Scenedesmus acutus (Chlorophiceae) / Bruno, L.; Cozza, D.; Ferrari, M.; Torelli, Anna; Marieschi, Matteo; Zanni, Corrado; Cozza, R.. - .:.(2014), pp. 72-72. (Intervento presentato al convegno 109° Congresso della Società Botanica Italiana. International Plant Conference (IPSC) From Nature to Technological Exploitation tenutosi a Firenze nel 2-5 Settembre 2014) [.].

A putative metallothionein from the microalga Scenedesmus acutus (Chlorophiceae).

TORELLI, Anna;MARIESCHI, Matteo;ZANNI, Corrado;
2014-01-01

Abstract

Microalgae are predominantly aquatic organisms that must be able to discriminate between essential and non-essential heavy metal ions. In addition, they must maintain non-toxic concentrations of these ions inside their cells. In this way, two principal mechanisms have been identified, one which prevents the indiscriminate entrance of heavy metal ions into the cell (i.e., exclusion) and the other which prevents bioavailability of these toxic ions once inside the cell (i.e., the formation of complexes). The molecules responsible for the first mechanism are extra-cellular polymers, mainly carbohydrates; those responsible for the second are essentially the two type metal-chelating peptides: enzymatically synthesized phytochelatins (PCs- class III metallothioneins -MtIII), and gene-encoded metallothioneins (MTs) (1). MTs are low molecular weight, cysteine-rich metal chelators with an ability to bind heavy metal ions through metal-thiolate bonds. In addition, the thiol(ate)s in MTs can act as powerful antioxidants, and hence MTs may have roles in protection against oxidative stress (2). Mts are widely distributed in animals, plants, fungi as well as cyanobacteria. Plant MTs (pMTs) are considerably longer than their animal counterparts owing to the exclusive presence of a 30-50 residue-long, Cys-devoid region, between the N- and C-terminal Cys-rich domains (four to eight Cys each). Specifically, the distribution of the Cys residues and the length of the spacer region have been used to further classify plant MTs into four subtypes (3, 4). Currently, pMTs have been extensively identified as a multigenic family in angiosperms (A. thaliana as a model) (3), in gymnosperms (5) and in macroalgae (Fucus) (6), constituting family 15 of the global MTs Kägi classification (7). To date, no evidences of genes encoding Mts in microalgae are reported, although the induction of cadmium-binding MT-like protein has been found in the unicellular algae Chlamidomonas sorokiniana (8) and Chlamidomonas vulgaris (9). In this work we reported the first evidence of a Mts gene from the microalga Scenedesmus acutus. In the case of the heavy metal tolerance of S. acutus, previous data report the implication of reduced glutathione (GSH) and Phytochelatins-MtIII as the molecular mechanism underlying the Cd tolerance (10). By RT-PCR amplification approach using degenerate primers, we amplified a full length cDNA of 280 bp sharing high identity with plant metallothioneins. The deduced protein consisted of 91 residues (mol wt of 9,2kDa) which contains 8 Cys residues arranged in CXC and CXXC motifs and showing a high identity homology (89%-98%) with other type2 Mts of the Silene genus. Despite this, the primary structures of Scenedesmus acutus MTs ( named ScaMT) shows some differences with the canonical pMts type 2 which relate it to an archetypal Type 2 sequences from other pMTs members. So, the evidence that ScaMT sequences shows similarity to Types 2 is a phylogenetically important finding and supports both the existence of a common ancestral metallothionein and its diversification at a point after the evolution of Chlorophyta and Streptophyta lineage. Work is in progress in order to define the genomic feature of ScaMT gene and its functional role (response to different heavy metals and/or stress condition). The results will also elucidate the different implications of the two type of heavy metal binding peptides (enzyme and encoding synthesized) in S. acutus in order to better understand the metal tolerance and/or the bioaccumulation mechanisms in this microalga. These molecular mechanism would be potential engineerized to improve the algal phytoremediation performance. 1) H.V. Perales-Vela, J.M. Peña-Castro, R.O. Cañizares-Villanueva (2006) Chemospere, 64, 1-10 2) V. H. Hassinen, A. I. Tervahauta, H. Schat, S.O. Karenlampi (2011) Plant Biol., 13, 225-232 3) C.S. Cobbett, P.B. Goldsbrough (2002) Annu. Rev. Plant Biol., 53, 159-182 4) N.J. Robinson, A.M. Tommey, C. Kuske, P.J. Jackson (1993) Biochem. J., 295, 1-10 5) M. Chatthai, K.H. Kaukinen, T.J. Tranbarger, P.K. Gupta, S. Misra (1997) Plant Mol. Biol. 34, 243-254 6) C.A. Morris, B. Nicolaus, V. Sampson, J.L. Harwood, P. Kille (1999) Biochem. J., 338, 553-560 7) P.A. Binz, J.H.R. Kägi (2001) Metallothionein. http://www. bioc.uzh.ch/mtpage/MT.html 8) N. Yoshida, K. Ishii, T. Okuno, K. Tanaka (2006) Current Microbiology, 52, 460-463 9) Z. Huang, L. Li, G. Huang, Q. Yan, B. Shi, X. Xu (2009) Aquat. Toxicol., 91, 54-61 10) E. Torricelli, G. Gorbi, B. Pawlik-Skowronska, L. Sanità di Toppi, M.G. Corradi (2004) Aquat. Toxicol., 68, 315-323
2014
A putative metallothionein from the microalga Scenedesmus acutus (Chlorophiceae) / Bruno, L.; Cozza, D.; Ferrari, M.; Torelli, Anna; Marieschi, Matteo; Zanni, Corrado; Cozza, R.. - .:.(2014), pp. 72-72. (Intervento presentato al convegno 109° Congresso della Società Botanica Italiana. International Plant Conference (IPSC) From Nature to Technological Exploitation tenutosi a Firenze nel 2-5 Settembre 2014) [.].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11381/2785152
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