Isolation and characterization of Arabidopsis halleri and Thlaspi caerulescens phytochelatin synthases

Abstract

The synthesis of phytochelatins (PC) represents a major metal and metalloid detoxification mechanism in various species. PC most likely play a role in the distribution and accumulation of Cd and possibly other metals. However, to date, no studies have investigated the phytochelatin synthase (PCS) genes and their expression in the Cd-hyperaccumulating species. We used functional screens in two yeast species to identify genes expressed by two Cd hyperaccumulators (Arabidopsis halleri and Thlaspi caerulescens) and involved in cellular Cd tolerance. As a result of these screens, PCS genes were identified for both species. PCS1 was in each case the dominating cDNA isolated. The deduced sequences of AhPCS1 and TcPCS1 are very similar to AtPCS1 and their identity is particularly high in the proposed catalytic N-terminal domain. We also identified in A. halleri and T. caerulescens orthologues of AtPCS2 that encode functional PCS. As compared to A. halleri and A. thaliana, T. caerulescens showed the lowest PCS expression. Furthermore, concentrations of PC in Cd-treated roots were the highest in A. thaliana, intermediate in A. halleri and the lowest in T. caerulescens. This mirrors the known capacity of these species to translocate Cd to the shoot, with T. caerulescens being the best translocator. Very low or undetectable concentrations of PC were measured in A. halleri and T. caerulescens shoots, contrary to A. thaliana. These results suggest that extremely efficient alternative Cd sequestration pathways in leaves of Cd hyperaccumulators prevent activation of PC synthase by Cd²⁺ ions.

Cadmium‐induced changes in glutathione and phenolics of Thlaspi and Noccaea species differing in Cd accumulation

“…In contrast, no GSH depletion under Cd exposure was observed in the hyperaccumulators. This is in line with several previous observations: low expression of PC synthase, the fact that PC synthase inhibition did not affect Cd resistance, the lower production of PCs in response to Cd found in these Cd hyperaccumulators, and the fact that hyperaccumulators do not detoxify the metals by huge accumulation of PCs, but by sequestering the metals into the vacuoles (Küpper et al, 2004;Meyer et al, 2011;Mijovilovich et al, 2009;Schat et al, 2002).…”

Arabidopsis thaliana phytochelatin synthase 2 is constitutively active in vivo and can rescue the growth defect of the PCS1-deficient cad1-3 mutant on Cd-contaminated soil

“…Legumes such as Lotus japonicus were found to carry three PCS genes probably originating from two duplication events (Ramos et al , 2007). Metal-hyperaccumulating Brassicaceae Arabidopsis halleri and Noccaea caerulescens both possess two PCS genes like their relative A. thaliana (Meyer et al , 2011). Therefore, a search for PCS2 -like genes among sequenced plant genomes was performed.…”

The use of the model species Arabidopsis halleri towards phytoextraction of cadmium polluted soils

“…Cd was reported to be mainly transported as free ion in the xylem sap of A. halleri and in shoots Cd seems to be bound to COOH/OH-containing (organic acids and/or cell wall components) and thiol containing molecules [40,58]. One of the major metal detoxification mechanisms in plants, the synthesis of phytochelatins, does not seem to play a major role in Cd tolerance and accumulation of A. halleri [40,59]. Phytochelatins were only detected in A. halleri roots at high concentration of Cd (i.e.…”