Boron toxicity tolerance in barley through reduced expression of the multifunctional aquaporin HvNIP2;1

Abstract

Boron (B) toxicity is a significant limitation to cereal crop production in a number of regions worldwide. Here we describe the cloning of a gene from barley, underlying the chromosome 6H B toxicity tolerance QTL. It is the second B toxicity tolerance gene identified in barley. Previously, we identified the gene HvBot1 which functions as an efflux transporter in B toxicity tolerant barley to move B out of the plant. The gene identified in this work encodes HvNIP2;1, an aquaporin from the NIP subfamily which was recently described as a silicon influx transporter in barley and rice. Here we show that a rice mutant for this gene also shows reduced B accumulation in leaf blades compared to wild type and that the mutant protein alters growth of yeast under high B. HvNIP2;1 facilitates significant transport of B when expressed in Xenopus oocytes compared to controls and to another NIP (NOD26), and also in yeast plasma membranes which appear to have relatively high B permeability. We propose that tolerance to high soil B is mediated by reduced expression of HvNIP2;1 to limit B uptake as well as by increased expression of HvBot1 to remove B from roots and sensitive tissues. Together with HvBot1, the multifunctional aquaporin HvNIP2;1 is an important determinant of B toxicity tolerance in barley.