Toxic metal, Lead (Pb) alters columella-specific auxin distribution inhibiting root growth and gravitropic response in Arabidopsis and maize

Abstract

Toxic metal contamination is pervasive throughout global soils and of significant concern due to its high abundance in agricultural lands. Contaminated soil detrimentally impacts the crops that grow in them and the humans that consume these crops. There is a need for engineering of plants able to grow in the presence of toxic metals while sequestering these contaminants away from edible tissues. However, engineering efforts require a detailed mechanistic understanding of plant responses to these toxins, which are currently lacking. In this study, we discovered that there are dissimilar root growth responses to different toxic metals. We found that the toxic metal lead (Pb) targets conserved cellular and developmental processes in evolutionary diverse plant systems - the model plant Arabidopsis thaliana and crop plant Zea mays. In Arabidopsis thaliana, Pb inhibits auxin transporter PIN FORMED 3 (PIN3) protein trafficking in the columella cells, which in turn alters the phytohormone auxin distribution, and consequently inhibits cell cycle progression and disrupts root gravitropic responses. Both root growth and gravitropic responses are critical for soil exploration, which requires plants to live and thrive in harsh environments.