ARS | Publication request: ALTERED ZN-DEPENDENT GENE REGULATION IN THLASPI CAERULESCENS PLAYS A KEY ROLE IN HEAVY METAL HYPERACCUMULATION

Submitted to: Plant Physiology
Publication Type: Abstract Only
Publication Acceptance Date: June 18, 2000
Publication Date: N/A

Technical Abstract: We recently cloned and characterized the heavy metal transporter, ZNT1, from the Zn/Cd hyperaccumulator, Thlaspi caerulescens. A study of ZNT1 expression and root Zn2+ uptake showed that alterations in the regulation of ZNT1 expression by plant Zn status results in the overexpression of this transporter and increased root Zn2+ influx. ZNT1 is a member of the ZIP gene family which encodes micronutrient transporters and includes 4 Zn transporters (ZIP1-4) from Arabidopsis. Expression analysis using members of the ZIP gene family, other micronutrient transporter genes, and non-transport genes implicated in heavy metal homeostasis in plants reveal a pattern of overexpression in T. caerulescens which is similar to that for ZNT1. This altered expression of a suite of genes relating to heavy metal transport/homeostasis in response to Zn status suggests that the Zn-dependent regulation of gene expression is an integral component of Zn hyperaccumulation in T. caerulescens. Although no information regarding Zn-dependent gene regulation has been elucidated in plants thus far, a Zn responsive regulatory pathway has recently been discovered in yeast (Zhou et al, 1997). The yeast ZIP family gene members, ZRT1 and ZRT2, share significant structural and sequence similarity with ZNT1, and expression of ZRT1 and ZRT2 was found to depend on cellular Zn2+ activity. This elegant regulatory mechanism appears to modulate the expression of ZRT1 and ZRT2 in response to cellular Zn2+ via a Zn responsive transcriptional activator protein, ZAP1, and Zn responsive elements (ZRE) in the promoters of ZRT1, ZRT2, and ZAP1. We are searching for similar regulatory components in Thlaspi, which may allow us to identify the key molecular components responsible for heavy metal hyperaccumulation.