Silicon accumulated in the shoots results in down-regulation of phosphorus transporter gene expression and decrease of phosphorus  uptake in rice.

Aims: Silicon (Si) as a beneficial element can improve nutrient imbalance, but the molecular mechanism for this effect is poorly understood. The objective of this study is to examine the mechanism underlying Si-induced decrease of phosphorus (P) uptake in rice (<italic>Oryza sativa</italic>) at adequate/high P supply.Method: A rice mutant (<italic>lsi1</italic>) defective in Si uptake and its wild type (cv. Oochikara) were used. The P uptake was compared in the presence and absence of Si and the expression of Pi transporter genes was quantified.Results: Si addition in the nutrient solution significantly decreased shoot P concentration and uptake in the WT, but not in <italic>lsi1</italic> mutant at two P levels, adequate (90 μM) and high (210 μM). Neither the root-to-shoot translocation of P nor the P distribution in different organs was altered by Si in both WT and <italic>lsi1</italic>. Heterogeneous expression of <italic>Lsi1</italic> in <italic>Xenopus</italic> oocyte did not show transport activity for Pi. The expression of Pi transporter genes (<italic>OsPT1</italic>, <italic>2</italic> and <italic>8</italic>) in the roots was hardly affected by Si in both WT and <italic>lsi1</italic>, but that of <italic>OsPT6</italic> was down-regulated by Si in the WT roots, but not in the <italic>lsi1</italic> roots. Furthermore, a split root experiment showed that Si accumulated in the shoots suppressed the expression of <italic>OsPT6</italic>. In rice grown in paddy field, <italic>lsi1</italic> showed higher P concentration in the straw, husk and brown rice than the WT.Conclusion: Si decreased P uptake through down-regulating the expression of P transporter gene, <italic>OsPT6</italic> in rice and Si accumulated in the shoot is required for this down-regulation. [ABSTRACT FROM AUTHOR]