Elevated expression of metal transporter genes in three accessions of the metal hyperaccumulator Thlaspi caerulescens

Abstract

Heavy metal hyperaccumulation in plants is an intriguing and poorly understood phenomenon. Transmembrane metal transporters are assumed to play a key role in this process. We describe the cloning and isolation of three zinc transporter cDNAs from the Zn hyperaccumulator Thlaspi caerulescens. The ZTP1 gene is highly similar to the Arabidopsis ZAT gene. Of the other two, one is most probably an allele of the recently cloned ZNT1 gene from T. caerulescens (Pence et al; Proceedings of the National Academy of Science USA 97, 4956-4960, 2000). The second, called ZNT2, is a close homologue of ZNT1. All three zinc transporter genes show increased expression in T. caerulescens compared with the non-hyperaccumulator congener T. arvense, suggesting an important role in heavy metal hyperaccumulation. ZNT1 and ZNT2 are predominantly expressed in roots and ZTP1 is mainly expressed in leaves but also in roots. In T. arvense, ZNT1 and ZNT2 are exclusively expressed under conditions of Zn deficiency. Their expression in T. caerulescens is barely Zn-responsive, suggesting that Zn hyperaccumulation might rely on a decreased Zn-induced transcriptional downregulation of these genes. ZTP1 expression was higher in plants from calamine soil than in plants from serpentine or normal soil. The calamine plants were also the most Zn tolerant, suggesting that high ZTP1 expression might contribute to Zn tolerance.

Growth and mineral element composition in two ecotypes of Thlaspi caerulescens on Cd contaminated soil

“…The high expression of Zn transporters in T. caerulescens has been suggested to be the mechanism for the enhanced Zn uptake of this species Pence et al, 2000). However, the difference in transporter expression among T. caerulescens ecotypes is not clearly associated with differences in Zn uptake between these accessions (Assunc¸a˜o et al, 2001).…”

“…Hyperaccumulation of Cd and Zn showed a strong positive correlation across the ecotypes, which may indicate that Cd and Zn partly share the same transport systems. The Zn transporter, ZNT1 (member of the ZIP family) cloned from the Prayon population has been shown to mediate high affinity Zn transport and low affinity Cd transport when expressed in yeast (Assunc¸a˜o et al, 2001;Pence et al, 2000).…”

Characteristics of cadmium accumulation and tolerance in Rorippa globosa (Turcz.) Thell., a species with some characteristics of cadmium hyperaccumulation

“…A unique physiology of Zn and Cd tolerance and transportation in T. caerulescens makes this species a very interesting experimental object for studying the mechanisms of heavy metal hyperaccumulation. Much previous work on T. caerulescens has only involved in Zn tolerance and hyperaccumulation (Assunçaõ et al 2001;Frey et al 2000;Küpper et al 1999;Lasat et al 2000). Recently, the comparable mechanisms for Cd have got more and more attention (Cosio et al 2004;Küpper et al 2004;Wójcik et al 2005Wójcik et al , 2006Liu et al 2008).…”

Responses to Nickel in the Proteome of the Hyperaccumulator Plant Alyssum lesbiacum

“…Although progress over the last few years has enhanced our understanding of the physiology of metal hyperaccumulation, insights into the molecular-biochemical basis of hyperaccumulation have only recently started to emerge. Greatest progress has been made in the identification of metal transport proteins whose transcripts are highly expressed in hyperaccumulator species, such as transporters of the ZIP gene family in the Zn/Cd hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri Assunc¸a˜o et al 2001;Lombi et al 2002;Becher et al 2004;Weber et al 2004), members of the cation diffusion facilitator family (Assunc¸a˜o et al 2001;Persans et al 2001;Becher et al 2004;Dra¨ger et al 2004;Kim et al 2004;Weber et al 2004), and the P-type ATPases HMA3 and HMA4 (Becher et al 2004;Bernard et al 2004;Papoyan & Kochian 2004;Weber et al 2004). In addition, hyperaccumulator plants appear to have highly effective antioxidant systems to protect against the potentially damaging effects of metalinduced reactive oxygen species (Freeman et al 2004).…”