Structural basis for high selectivity of a rice silicon channel Lsi1

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 in aquaporin and shows high selectivity for silicic acid. To uncover the structural basis for this high selectivity, here we show the crystal structure of the rice Lsi1 at a resolution of 1.8 Å. The structure reveals transmembrane helical orientations different from other aquaporins, characterized by a unique, widely opened, and hydrophilic selectivity filter (SF) composed of five residues. Our structural, functional, and theoretical investigations provide a solid structural basis for the Si uptake mechanism in plants, which will contribute to secure and sustainable rice production by manipulating Lsi1 selectivity for different metalloids

The grapevine (Vitis vinifera) aquaporin VvNIP2;1 is a silicon channel localized at the plasma membrane highly expressed in roots

Silicon (Si) supplementation has been shown to improve plant tolerance to different stresses and its accumulation in the aerial organs is mediated by NIP2;1 aquaporins (Lsi channels) and Lsi2-type exporters in roots. In the present study, we tested the hypothesis that grapevine expresses a functional NIP2;1 that accounts for root Si uptake and, eventually, Si accumulation in leaves. Own-rooted grapevine cuttings of the cultivar Vinhão accumulated over 0.2 % Si (dw) in leaves when irrigated with 1.5 mM Si for one month, while Si was undetected in control leaves. Real-time PCR showed that VvNIP2;1 was highly expressed in roots and in green berries. The transient transformation of tobacco leaf epidermal cells mediated by Agrobacterium tumefaciens confirmed VvNIP2;1 localization at the plasma membrane. Transport experiments in oocytes showed that VvNIP2;1 mediates Si and arsenite uptake, whereas permeability studies revealed that VvNIP2;1 expressed in yeast is unable to transport water and glycerol. Si supplementation to pigmented grape cultured cells (cv. Gamay Freáux) had no impact on the total phenolic and anthocyanin content, as well as the growth rate and VvNIP2;1 expression. Long-term experiments should help determine the extent of Si uptake over time and if gapevine can benefit from Si fertilizationinfo:eu-repo/semantics/acceptedVersio

Prevention and Recovery of COVID-19 Patients With Kampo Medicine: Review of Case Reports and Ongoing Clinical Trials

Coronavirus disease 2019 (COVID-19) spread to Japan in 2020, where the number of infected patients exceeded 250,000 and COVID-related deaths exceeded 3,500 in one year. Basic guidelines for infection control were implemented in Japan, and research and development of effective drugs and vaccines were promoted. This included considering Kampo medicine, which has a long history of treating recurring emerging viral infections. Considering the characteristics of the disease (inflammation of the upper and lower respiratory tract as well as potential neural damage and vasculitis), Kampo medicine could be considered as a treatment strategy due to its antiviral and anti-inflammatory effects induced by multiple active substances that could aid in disease prevention and recovery. In this study, case reports on the management of COVID-19 with Kampo medicine, which were published until March 31, 2021, were reviewed. The search strategy involved the use of Medline and hand-searching. Twenty two patients were treated using Kampo medicines with or without Western medicine, based on individual conditions. On the other hand, the effects of Kampo medicines as a potential preventive treatment (pre-infection), active treatment (especially in the acute and subacute stage), or treatment of sequelae to aid recovery (after infection) in the different stages of COVID-19 are being studied as research projects in the Japan Society for Oriental Medicine (JSOM). JSOM has also organized a pioneering project of clinical trials for COVID-19, some of which are now in progress

The aromatic/arginine selectivity filter of NIP aquaporins plays a critical role in substrate selectivity for silicon, boron, and arsenic

Nodulin-26-like intrinsic proteins (NIPs) of the aquaporin family are involved in the transport of diverse solutes, but the mechanisms controlling the selectivity of transport substrates are poorly understood. The purpose of this study was to investigate how the aromatic/arginine (ar/R) selectivity filter influences the substrate selectivity of two NIP aquaporins; the silicic acid (Si) transporter OsLsi1 (OsNIP2;1) from rice and the boric acid (B) transporter AtNIP5;1 from Arabidopsis; both proteins are also permeable to arsenite. Native and site-directed mutagenized variants of the two genes were expressed in Xenopus oocytes and the transport activities for Si, B, arsenite, and water were assayed. Substitution of the amino acid at the ar/R second helix (H2) position of OsLsi1 did not affect the transport activities for Si, B, and arsenite, but that at the H5 position resulted in a total loss of Si and B transport activities and a partial loss of arsenite transport activity. Conversely, changes of the AtNIP5;1 ar/R selectivity filter and the NPA motifs to the OsLsi1 type did not result in a gain of Si transport activity. B transport activity was partially lost in the H5 mutant but unaffected in the H2 mutant of AtNIP5;1. In contrast, both the single and double mutations at the H2 and/or H5 positions of AtNIP5;1 did not affect arsenite transport activity. The results reveal that the residue at the H5 position of the ar/R filter of both OsLsi1 and AtNIP5;1 plays a key role in the permeability to Si and B, but there is a relatively low selectivity for arsenite

The role of the rice aquaporin Lsi1 in arsenite efflux from roots

When supplied with arsenate (As(V)), plant roots extrude a substantial amount of arsenite (As(III)) to the external medium through as yet unidentified pathways. The rice (Oryza sativa) silicon transporter Lsi1 (OsNIP2;1, an aquaporin channel) is the major entry route of arsenite into rice roots. Whether Lsi1 also mediates arsenite efflux was investigated. Expression of Lsi1 in Xenopus laevis oocytes enhanced arsenite efflux, indicating that Lsi1 facilitates arsenite transport bidirectionally. Arsenite was the predominant arsenic species in arsenate-exposed rice plants. During 24-h exposure to 5 mu M arsenate, rice roots extruded arsenite to the external medium rapidly, accounting for 60-90% of the arsenate uptake. A rice mutant defective in Lsi1 (lsi1) extruded significantly less arsenite than the wild-type rice and, as a result, accumulated more arsenite in the roots. By contrast, Lsi2 mutation had little effect on arsenite efflux to the external medium. We conclude that Lsi1 plays a role in arsenite efflux in rice roots exposed to arsenate. However, this pathway accounts for only 15-20% of the total efflux, suggesting the existence of other efflux transporters

Identification of a mammalian silicon transporter.

Silicon (Si) has long been known to play a major physiological and structural role in certain organisms, including diatoms, sponges, and many higher plants, leading to the recent identification of multiple proteins responsible for Si transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding about the biochemical pathways that enable Si homeostasis. Here we report the identification of a mammalian efflux Si transporter, namely Slc34a2 (also termed NaPiIIb), a known sodium-phosphate cotransporter, which was upregulated in rat kidney following chronic dietary Si deprivation. Normal rat renal epithelium demonstrated punctate expression of Slc34a2, and when the protein was heterologously expressed in Xenopus laevis oocytes, Si efflux activity (i.e., movement of Si out of cells) was induced and was quantitatively similar to that induced by the known plant Si transporter OsLsi2 in the same expression system. Interestingly, Si efflux appeared saturable over time, but it did not vary as a function of extracellular [Formula: see text] or Na+ concentration, suggesting that Slc34a2 harbors a functionally independent transport site for Si operating in the reverse direction to the site for phosphate. Indeed, in rats with dietary Si depletion-induced upregulation of transporter expression, there was increased urinary phosphate excretion. This is the first evidence of an active Si transport protein in mammals and points towards an important role for Si in vertebrates and explains interactions between dietary phosphate and silicon

Maize silicon transporters

Maize (Zea mays L.) is a Si-accumulating species although its accumulation is not as high as rice. However, the transporters involved in Si uptake and distribution are unknown. Here, we isolated and characterized three maize silicon transporter genes ZmLsi1, ZmLsi2 and ZmLsi6, which are homologues, respectively, of rice silicon transporter genes. Each transporter shared more than 80% between maize and rice at amino acid level. Both ZmLsi1 and ZmLsi6 showed Si influx transport activity, while ZmLsi2 showed efflux activity, when they were expressed in Xenopus laevis oocytes. mRNA of ZmLsi1 and ZmLsi2 was expressed mainly in the roots, while ZmLsi6 was also in the shoots. Immunostaining showed that ZmLsi1 was localized at the distal side of plasma membrane of root epidermis, hypodermis and cortex, while ZmLsi2 was only in the endodermis without polarity. In contrast, ZmLsi6 was localized at the xylem parenchyma cells of the leaf blades. These results suggest that ZmLsi1 and ZmLsi2 are involved in the uptake of Si from the roots and ZmLsi6 is responsible for transport of Si out of the xylem, therefore regulating Si distribution in the leaves

Boron Uptake Assay in Xenopus laevis Oocytes

Boron (B) is essential for plant growth and taken up by plant roots as boric acid. Under B limitation, B uptake and translocation in plants are dependent on the boric acid channels located in the plasma membrane. Xenopus leavis oocyte is a reliable heterologous expression system to characterize transport activities of boric acid channels and related major intrinsic proteins (aquaporins). Here, we outline the protocols for expression of boric acid channels and boric acid uptake assay in Xenopus leavis oocytes