The molecular physiology of heavy metal transport in the Zn/Cd hyperaccumulator Thlaspi caerulescens

An integrated molecular and physiological investigation of the fundamental mechanisms of heavy metal accumulation was conducted in Thlaspi caerulescen s. a Zn/Cd-hyperaccumulating plant species. A heavy metal transporter cDNA, ZNT1, was cloned from T. caerulescens through functional complementation i n yeast and was shown to mediate high-affinity Zn2+ uptake as well as low-a ffinity Cd2+ uptake. It was found that this transporter is expressed at ver y high levels in roots and shoots of the hyperaccumulator, A study of ZNT1 expression and high-affinity Zn2+ uptake in roots of T, caerulescens and in a related nonaccumulator. Thlaspi arvense, showed that alteration in the r egulation of ZNT1 gene expression by plant Zn status results in the overexp ression of this transporter and in increased Zn influx in roots of the hype raccumulating Thlaspi species. These findings yield insights into the molec ular regulation and control of plant heavy metal and micronutrient accumula tion and homeostasis, as well as provide information that will contribute t o the advancement of phytoremediation by the future engineering of plants w ith improved heavy metal uptake and tolerance.