Molecular mechanisms of boron toxicity and identification of boron metabolim genes

Abstract

Boron is an essential micronutrient for plants and it is either necessary or beneficial for animals. Studies identified only few genes related to boron metabolism thus far and details of how boron is imported into cells and used in cell metabolism are largely unknown. In this study, in order to identify genes that play role in boron metabolism, the entire set of yeast haploid deletion mutants was screened and 6 boron resistant and 21 boron sensitive mutants were identified. Boron treatment activated the expression of ATR1 and many genes that are regulated by genereal amino acid control in a GCN4 dependent manner. Polysome analyses and 35-S methionine labelling assays suggested that boron inhibits protein synthesis. Inhibition of protein synthesis was also confirmed by the phosphorylation of translation factor eIF2. in boron treated cells, and phosphorylation of eIF2. was totally dependent on the uncharged tRNA binding domain of Gcn2 kinase. Overall, our results revealed many genes and pathways related to boron stress response and suggest a possible link between boron toxicity and translational control.