Functional Characterization of a Silicon Transporter Gene Implicated in Silicon Distribution in Barley    

Abstract

Silicon (Si) is a beneficial element for plant growth. In barley (Hordeum vulgare), Si uptake by the roots is mainly mediated by a Si channel, Low Silicon1 (HvLsi1), and an efflux transporter, HvLsi2. However, transporters involved in the distribution of Si in the shoots have not been identified. Here, we report the functional characterization of a homolog of HvLsi1, HvLsi6. HvLsi6 showed permeability for Si and localized to the plasma membrane. At the vegetative growth stage, HvLsi6 was expressed in both the roots and shoots. The expression level was unaffected by Si supply. In the roots, HvLsi6 was localized in epidermis and cortex cells of the tips, while in the leaf blades and sheaths, HvLsi6 was only localized at parenchyma cells of vascular bundles. At the reproductive growth stage, high expression of HvLsi6 was also found in the nodes. HvLsi6 in node I was polarly located at the transfer cells surrounding the enlarged vascular bundles toward the numerous xylem vessels. These results suggest that HvLsi6 is involved in Si uptake in the root tips, xylem unloading of Si in leaf blade and sheath, and intervascular transfer of Si in the nodes. Furthermore, HvLsi2 was found to be localized at the parenchyma cell layer adjacent to the transfer cells with opposite polarity of HvLsi6, suggesting that the coupling of HvLsi6 and HvLsi2 is involved in the intervascular transfer of Si at the nodes. Si translocated via the enlarged vascular bundles is unloaded to the transfer cells by HvLsi6, followed by HvLsi2 to reload Si to the diffuse vascular bundles, which are connected to the upper part of the plant, especially the panicles, the ultimate Si sink.

Can silicon partially alleviate micronutrient deficiency in plants? a review

“…Similar findings were observed in wild and cultivated rice (Mitani-Ueno et al 2013). In addition to rice, similar Si transporters were found in other grasses such as maize, barley and wheat (Mitani et al 2009a, b;Chiba et al 2009;Montpetit et al 2012;Yamaji et al 2012).…”

Low-molecular weight organic acids and peptides involved in the long-distance transport of trace metals

“…Recent study in barley (Hordeum vulgare) showed that a silicon transporter HvLsi6 is localized to the plasma membrane at parenchyma cells of vascular bundles and (during reproductive stage) in nodes. This data obtained by Yamaji et al (2012) suggested a role of HvLsi6 in Si xylem unloading in leaf blade and sheath along with intervascular transfer of Si in nodes. Considering homologous transporter OsLsi2 has a similarity level of 82 % in amino acids sequence and is able to mediate efflux of As, HvLsi6 might play a role in xylem unloading of As(III) in graminaceous plants (Ma 2009;Yamaji et al 2012).…”

“…This data obtained by Yamaji et al (2012) suggested a role of HvLsi6 in Si xylem unloading in leaf blade and sheath along with intervascular transfer of Si in nodes. Considering homologous transporter OsLsi2 has a similarity level of 82 % in amino acids sequence and is able to mediate efflux of As, HvLsi6 might play a role in xylem unloading of As(III) in graminaceous plants (Ma 2009;Yamaji et al 2012). transporters and channels in planta (including: ZIP family, Nramp family, LCT1 channels) (Gallego et al 2012).…”

Orchestration of three transporters and distinct vascular structures in node for intervascular transfer of silicon in rice

“…Recently, identification of mineral nutrient transporters in node and physiological studies shed a new light on the importance of node for preferential distribution of mineral nutrients to developing and reproductive organs (2,14,(18)(19)(20)(21)(22)(23). The xylem flow in EVBs and DVBs, which are connected by nodal vascular anastomosis (NVA) at the base of the node, are simply divided following the transpiration rate of each upper organ.…”