2 - P-type ATPases and their role in metal homeostasis in plants

Abstract

Hyperaccumulators are plants that can sequester heavy metals in their vacuoles and are capable of tolerating high amounts of such heavy metals. The metal tolerance mechanism is facilitated by overexpression of certain metal transport and binding proteins such as heavy metal transporters, phytochelatins, metallothioneins, etc. in various tissues. P-type ATPases constitute a large and diverse superfamily of transport proteins, which are of great importance in all organisms. They play a significant role in the maintenance of transition metal homeostasis, which, in turn, is extremely important for normal plant functioning. These proteins transport various metal ions such as Cu2+, Cd2+, Zn2+, Ca2+, H+, etc. across the cell membrane by a process characterized by hydrolysis of ATP during which a phosphorylated intermediate is formed. In addition to their role in metal hyperaccumulation, these proteins also help in the transport of metals to subcellular components and target proteins, metal detoxification, and micronutrient nutrition. This chapter describes the basic mechanism by which these proteins transport metals across the cell membrane, their classification of P-type ATPases based on the substrate(s) translocated by them, and the role of each type of P-type ATPase in maintaining metal homeostasis.