1.A.8.12.2
The silicon (silicic acid) (undissociated form) transporter, Lsi1 (Ma et al., 2007a, b; Mitani et al., 2008). The barley orthologue Lsi1 (also called NIP2-1) is also a silicon (silicic acid) uptake channel (Chiba et al., 2009). Rice Lsi1 also transports arsenite and pentavalent mono and dimethyl arsenite (Li et al., 2009). In addition to silicon (Si), selenite (Se) uptake is mediated by Lsi1 (Zhao et al., 2010).  Physicochemical and transcriptomic responses of Lactobacillus brevis JLD715 to sodium selenite have been reported (Yang et al. 2021). Many of the world's most important food crops such as rice, barley and maize accumulate silicon (Si) to high levels, resulting in better plant growth and crop yields (van den Berg et al. 2021). The first step in Si accumulation is the uptake of silicic acid by the roots, a process mediated by the NIP subfamily of aquaporins, also named metalloid porins. van den Berg et al. 2021 presented the X-ray crystal structure of the archetypal NIP family member from Oryza sativa (OsNIP2;1). The OsNIP2;1 channel is closed in the crystal structure by the cytoplasmic loop D, which is known to regulate channel opening in classical plant aquaporins. The structure reveals a novel, five-residue extracellular selectivity filter with a large diameter. Unbiased molecular dynamics simulations show a rapid opening of the channel to visualise how silicic acid interacts with the selectivity filter prior to transmembrane diffusion. These results may enable detailed structure-function studies of metalloid porins, including the basis of their substrate selectivity (van den Berg et al. 2021). Silicon (Si), the most abundant mineral element in the earth's crust, is taken up by plant roots in the form of silicic acid through Low silicon rice 1 (Lsi1). Lsi1 belongs to the Nodulin 26-like intrinsic protein subfamily and shows high selectivity for silicic acid. The crystal structure of rice Lsi1 at a resolution of 1.8 Å reveals transmembrane helical orientations different from other aquaporins, characterized by a unique, widely opened, and hydrophilic selectivity filter composed of five residues. Structural, functional, and theoretical investigations provided a solid basis for the Si uptake mechanism in plants (Saitoh et al. 2021).

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