Hyper-accumulation capability of Silene vulgaris in relation to its phylogenyChi-Cheng Lin and Bruno Borsari

Winona State UniversityWinona, MN 55987

Introduction

Fig. 1 Silene vulgaris (Moench.)

Several plant species have been identified and employed for years in bioremediation efforts (Peuke and Rennenberg, 2005). Among these the species Silene vulgaris (Moench.) has been utilized for similar purposes (especially for the up-take of copper and zinc from soils) in European countries.

The purpose of this work consisted in reviewing current literature to learn the absorption modality of these ions by the plant under study, identify the genes involved in the process and locate the evolution of this trait in the phylogenetic tree of the species.

Mechanism of soil detoxification by Silene spp.

Discussion

Conclusion

Peuke and Rennenberg (2005) pointed out that mechanisms of phytoextraction evolved to tolerate naturally occurring heavy metals in the soil. Plants possess the capability of detoxifying soils from metal concentrations in a variety of processes, including metal binding to mychorrizal fungi (Le Gac et al., 2007). Chelation and transport of these metals is completed in the plant’s above-ground tissues where their sequestration occurs in the vacuoles (Peuke and Rennenberg, 2005), (Fig. 2).

Fig. 2. Mechanism of detoxification of heavy metals. (Peuke and Rennenberg, 2005)

ReferencesCobbett, C. and P. Goldsbrough, Phytochelatins and Metallothioneins: Roles in Heavy Metal Detoxification and Homeostasis, Annu. Rev. Plant Biol. 2002. 53:159-82.Le Gac, M., M. E. Hood, E. Fournier, and T. Giraud, Phylogenetic Evidence of Host-Specific Cryptic Species in the Anther Smut Fungus, Evolution, 61(1):15-26, January 2007.Peuke, A. D. and H. Rennenberg, Phytoremediation, EMBO Reports 6(6):497-501, 2005.Schat, H., R. Vooijs, and E. Kuiper, Identical Major Gene Loci for Heavy Metal Tolerances that Have Independently Evolved in Different Local Populations and Subspecies of Silene vulgaris, Evolution, 50(5):1888-1895, October, 1996.

Fig. 3. Summary of the phylogenetic relationships established between S. vulgaris and other closely related plants (Le Gac et al., 2007).

Two groups of metal-binding proteins, phytochelatins and metallothioneins, are involved in the process (Cobbett and Goldsbrough, 2002). In their paper, two sets of genes related to the two proteins respectively have been identified.

Various methods such as Bayesian, MP, and NJ were used to build the four trees (Le Gac et al., 2007). Figure 3 shows the summary of the phylogenetic tree obtained from four trees built using three genes and the combination of the three genes.

The group MvSv1 includes of two spp of S. maritima and three spp of S. vulgaris, whereas the group MvSv2 three spp of S. vulgaris.

According to this study, the tree shows that there is a consensus on where the group MvSv2 is in the tree, but it is not the case for MvSv1.

Phytoremediation is a promising approach to the environmental recovery of degraded soils however, despite the utilization of valuable plant species like Silene vulgaris several research questions remain unanswered. Schat et al., (1996) pointed out that there is only a limited degree of genetic variation among the population of Silene that was studied. Peuke and Rennenberg (2005) indicated that more work needs to be done in order to better understand the biosynthesis of the proteins (phytochelatins and metallothienins) involved in the process of metal up-take. We support their recommendations with the need to include more plant species in future bioremediation studies.