Understanding aquaporins regulation and silicon uptake in carrot ( Daucus carota )

Aquaporins play a vital role in uptake and transport of water and many other small solutes in plants. A genome-wide search performed in the carrot genome leads to identification of 47 aquaporins. Subsequent, computational analysis and phylogenetic classification of carrot aquaporins predicted DcNIP2-1 as a silicon transporter. The DcNIP2-1 is a member of NIPIII class of the Nodulin-26 like Intrinsic Protein (NIP) subfamily of aquaporins which is known to regulate uptake of silicon and other metalloids like arsenic and Germanium. Despite having NIP2-1 with functionality defining features like G-S-G-R aromatic/arginine (ar/R) selectivity filter, 108 amino acid spacing between two NPA motif, Mitani’s residue and desired pore morphology, carrot plants found to be silicon poor accumulator. Subsequently, pot-experiments were performed to confirm the uptake of other metalloids, and silicon derived benefits in carrot. Carrot plants were grown with arsenic and with or without silicon supplementation. The results obtained neither showed silicon accumulation, nor any significant benefits to carrot plants under arsenic stress. Similarly, very less accumulation of arsenic was observed in carrot leaves. Such low accumulation of silicon was consistent across different Apiaceae species. The information provided here will be helpful to better understand aquaporin regulation and more particularly silicon uptake and silicon derived benefits in Apiaceae and other plant species.