OsPT2, a phosphate transporter, is involved in the active uptake of selenite in rice

Abstract

• Selenite is a predominant form of selenium (Se) available to plants, especially in anaerobic soils, but the molecular mechanism of selenite uptake by plants is not well understood. • ltn1, a rice mutant previously shown to have increased phosphate (Pi) uptake, was found to exhibit higher selenite uptake than the wild-type in both concentration- and time-dependent selenite uptake assays. Respiratory inhibitors significantly inhibited selenite uptake in the wildtype and the ltn1 mutant, indicating that selenite uptake was coupled with H(+) and energy-dependent. Selenite uptake was greatly enhanced under Pi-starvation conditions, suggesting that Pi transporters are involved in selenite uptake. • OsPT2, the most abundantly expressed Pi transporter in the roots, is also significantly up-regulated in ltn1 and dramatically induced by Pi starvation. OsPT2-overexpressing and knockdown plants displayed significantly increased and decreased rates of selenite uptake, respectively, suggesting that OsPT2 plays a crucial role in selenite uptake. Se content in rice grains also increased significantly in OsPT2-overexpressing plants. • These data strongly demonstrate that selenite and Pi share similar uptake mechanisms and that OsPT2 is involved in selenite uptake, which provides a potential strategy for breeding Se-enriched rice varieties.

Keywords: molecular mechanism; phosphate transporter; rice (Oryza sativa); selenite uptake; selenium (Se).

Figure 1

Difference in concentration- (a) and time-dependent (b) selenite uptake by roots of Nipponbare (Oryza sativa; squares) and its mutant ltn1 (triangles). Error bars indicate mean values ± SD (n = 5).

Figure 2

Effects of phosphorus (P) and sulfur (S) starvation on selenium (Se) concentration in roots of Nipponbare (the wild-type, Oryza sativa) and its mutant ltn1. Error bars indicate mean values ± SD (n = 5). Asterisks indicate the significant differences between the wild-type and ltn1 as determined by Student's t-test: **, P < 0.01. Control, black bars; no P, gray bars; no S, white bars.

Figure 3

Effects of carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP) on selenite uptake by roots of Nipponbare (the wild-type, Oryza sativa) and ltn1. Error bars indicate mean values ± SD (n = 5). Asterisks indicate the significant differences between the wild-type and ltn1 as determined by Student's t-test: **, P < 0.01. Control, black bars; CCCP, gray bars; DNP, white bars.

Figure 4

Effect of phosphorus (P) on gene expression of Pi transporters in roots of Nipponbare (the wild-type, Oryza sativa; black bars) and ltn1 (gray bars) under Pi-sufficient (a) and Pi-deficient (b) conditions. Error bars indicate mean values ± SD (n = 3).

Figure 5

Expression of the OsPT2 gene in Zhonghua11 (Oryza sativa) and OsPT2 transgenic lines. Ox-1 and Ox-3 are two OsPT2-overexpressing lines; Ri-2 and Ri-5 are two OsPT2-RNAi lines. Error bars indicate mean values ± SD (n = 3). Asterisks indicate the significant differences between Zhonghua11 and OsPT2 transgenic lines as determined by Student's t-test: **, P < 0.01.

Figure 6

(a) Difference in selenite uptake by roots of Zhonghua11 (Oryza sativa) and OsPT2 transgenic lines. (b) Difference in selenium (Se) concentration in roots and shoots of Zhonghua11 and transgenic lines. Ox-1 and Ox-3 are two OsPT2-overexpressing lines; Ri-2 and Ri-5 are two OsPT2-RNAi lines. Error bars indicate mean values ± SD (n = 3). Asterisks indicate the significant differences between Zhonghua11 and OsPT2 transgenic lines as determined by Student's t-test: *, P < 0.05; **, P < 0.01.

Figure 7

(a) OsPT2 tissue location in young root detected by mRNA in situ hybridization. The OsPT2 signal was detected in the epidermal tissue (indicated by a red arrow) of the primary roots of Zhonghua11 (Oryza sativa). (b) Negative control preparation made with an OsPT2 sense probe.

Figure 8

Selenium (Se) concentration in rice grains of Zhonghua11 (Oryza sativa) and OsPT2 transgenic lines. Ox-1 and Ox-3 are two OsPT2-overexpressing lines; Ri-2 and Ri-5 are two OsPT2-RNAi lines. Error bars indicate mean values ± SD (n = 3). Asterisks indicate the significant differences between Zhonghua11 (Oryza sativa) and OsPT2 transgenic lines as determined by Student's t-test: *, P < 0.05.