Abstract
We have identified both influx and efflux Si transporters from rice, barley and maize. They all show similar transport activity for Si in Xenopus oocytes. However, the Si uptake capacity greatly differs between rice and barley or maize. To understand the mechanism underlying the species-dependent difference in Si uptake, we compared the expression level and localization pattern of Si transporters between rice and barley. Analysis with absolute quantitative real time PCR showed that the mRNA level of Lsi1 and Lsi2 was several-fold higher in rice than in barley. When HvLsi1 or OsLsi1 were introduced into a rice lsi1 mutant under the control of HvLsi1 promoter, both HvLsi1 and OsLsi1 were localized at the distal side of root exodermis and endodermis, which is similar to the native rice Lsi1. Although the mRNA level in both transgenic lines was similar, Si uptake by HvLsi1-expressed rice was lower than in that OsLsi1-expressed lines. Our results suggest that both higher expression level and transport activity of Lsi1 contribute to a higher Si uptake capacity in rice. Similar analysis with Lsi2 is currently being undertaken.
