Rice Plasma Membrane Intrinsic Proteins Play Critical Role in Arsenite and Boron Transport and Providing Tolerance in Plants.

Rice Plasma Membrane Intrinsic Proteins Play Critical Role in Arsenite and Boron Transport and Providing Tolerance in Plants Om Parkash Dhankher, Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003; parkash@umass.edu Kareem Mosa, Department of Applied Biology, University of Sharjah, United Arab Emirates Kundan Kumar, Department of Biological Sciences, Birla Institute of Technology & Science Pilani, K.K. Birla Goa Campus, Goa 403726, India Ahmed Gameel, Stockbridge School of Agriculture, University of Massachusetts, Amherst, MA 01003 Metalloid arsenite (AsIII) and boron (B) are phytotoxic and cause severe decline in crop productivity worldwide. Rice accumulates high level of arsenic (As) in its edible parts and thus plays an important role in the transfer of As into the food chain. However, the mechanisms of As uptake and its detoxification in rice are not well understood. Recently, Silicon transporters belonging to the Nodulin 26-like Intrinsic Protein (NIP) subfamily of plant aquaporins were shown to transport AsIII and B in rice and Arabidopsis. Rice requires 10-12% silicates for the mechanical strength and stress tolerance. Therefore, blocking the function of NIPs to reduce AsIII and B accumulation in rice will severely compromise rice growth and yield. To identify genes that are specific to AsIII and B transport in rice, we analyzed the role of the Plasma Membrane Intrinsic Proteins (PIPs) subfamily of aquaporins for their involvement in AsIII and B transport and tolerance. We provided experimental evidences showing that members of rice PIP subfamily are involved in AsIII and B permeability in plants. Heterologous expression of rice PIP in Xenopus laevis oocytes confirmed their role in AsIII transport. Further, expression of rice PIP genes in yeast strain lacking the metalloids influx and efflux systems resulted in an increased B sensitivity and accumulation. Overexpression of rice PIP genes in Arabidopsis yielded enhanced AsIII and B tolerance without causing an increase in As and B accumulation. Short-term influx and efflux assay for AsIII and B transport suggested a bidirectional transport activity of rice PIPs. Our results clearly showed that PIPs genes will be highly useful in developing AsIII and B tolerant crops for enhanced yield in the areas affected by high As and B toxicity without causing accumulation in the aboveground biomass and grains.