Silicon (Si) accumulation in shoots differs greatly with plant species, but the molecular mechanisms for this interspecific difference are unknown. Here, we isolated homologous genes of rice Si influx (SlLsi1) and efflux (SlLsi2) transporter genes in tomato (Solanum lycopersicum L.) and functionally characterized these genes. SlLsi1 showed transport activity for Si when expressed in both rice lsi1 mutant and Xenopus laevis oocytes. SlLsi1 was constitutively expressed in the roots. Immunostaining showed that SlLsi1 was localized at the plasma membrane of both root tip and basal region without polarity. Furthermore, overexpression of SlLsi1 in tomato increased Si concentration in the roots and root cell sap but did not alter the Si concentration in the shoots. By contrast, two Lsi2-like proteins did not show efflux transport activity for Si in Xenopus oocytes. However, when functional CsLsi2 from cucumber was expressed in tomato, the Si uptake was significantly increased, resulting in higher Si accumulation in the leaves and enhanced tolerance of the leaves to water deficit and high temperature. Our results suggest that the low Si accumulation in tomato is attributed to the lack of functional Si efflux transporter Lsi2 required for active Si uptake although SlLsi1 is functional.

中文翻译：

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番茄根具有功能性硅流入转运蛋白，但没有功能性硅外流转运蛋白。

芽中硅（Si）的积累因植物种类而有很大差异，但这种种间差异的分子机制尚不清楚。在这里，我们分离了水稻（番茄Solanum lycopersicum L.）的水稻Si流入（SlLsi1）和外排（SlLsi2）转运蛋白基因的同源基因，并对这些基因进行了功能鉴定。当在水稻lsi1突变体和非洲爪蟾卵母细胞中表达时，SlLsi1显示出对Si的转运活性。S1Lsi1在根中组成性表达。免疫染色显示SlLsi1定位在根尖和基底区域的质膜上，没有极性。此外，番茄中SlLsi1的过表达增加了根和根细胞汁液中的硅含量，但并未改变芽中的硅含量。相比之下，在非洲爪蟾卵母细胞中，两个类似Lsi2的蛋白没有显示出Si的外排转运活性。但是，当在番茄中表达来自黄瓜的功能性CsLsi2时，Si的吸收显着增加，从而导致叶片中更高的Si积累并增强了叶片对水分缺乏和高温的耐受性。我们的研究结果表明，尽管SlLsi1具有功能性，但番茄中低的Si积累是由于缺乏有效的Si吸收所需的功能性Si外排转运蛋白Lsi2。