The rice aquaporin Lsi1 mediates uptake of methylated arsenic species.
Pentavalent methylated arsenic (As) species such as monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] are used as herbicides or pesticides, and can also be synthesized by soil microorganisms or algae through As methylation. The mechanism of MMA(V) and DMA(V) uptake remains unknown. Recent studies have shown that arsenite is taken up by rice (Oryza sativa) roots through two silicon transporters, Lsi1 (the aquaporin NIP2;1) and Lsi2 (an efflux carrier). Here we investigated whether these two transporters also mediate the uptake of MMA(V) and DMA(V). MMA(V) was partly reduced to trivalent MMA(III) in rice roots, but only MMA(V) was translocated to shoots. DMA(V) was stable in plants. The rice lsi1 mutant lost about 80% and 50% of the uptake capacity for MMA(V) and DMA(V), respectively, compared with the wild-type rice, whereas Lsi2 mutation had little effect. The short-term uptake kinetics of MMA(V) can be described by a Michaelis-Menten plus linear model, with the wild type having 3.5-fold higher V(max) than the lsi1 mutant. The uptake kinetics of DMA(V) were linear with the slope being 2.8-fold higher in the wild type than the lsi1 mutant. Heterologous expression of Lsi1 in Xenopus laevis oocytes significantly increased the uptake of MMA(V) but not DMA(V), possibly because of a very limited uptake of the latter. Uptake of MMA(V) and DMA(V) by wild-type rice was increased as the pH of the medium decreased, consistent with an increasing proportion of the undissociated species. The results demonstrate that Lsi1 mediates the uptake of undissociated methylated As in rice roots.
Li
Ren-Ying
RY
Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom.
Ago
Yukiko
Y
Liu
Wen-Ju
WJ
Mitani
Namiki
N
Feldmann
Jörg
J
McGrath
Steve P
SP
Ma
Jian Feng
JF
Zhao
Fang-Jie
FJ
D000818:Animals; D020346:Aquaporins / Q000378:metabolism*; D001151:Arsenic / Q000302:isolation & purification / Q000378:metabolism*; D001152:Arsenicals / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002101:Cacodylic Acid / Q000378:metabolism / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007700:Kinetics; D013058:Mass Spectrometry; D008745:Methylation / Q000187:drug effects; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D012275:Oryza / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D012996:Solutions; D014982:Xenopus laevis
D020346:Aquaporins; D001152:Arsenicals; D003470:Culture Media; D010940:Plant Proteins; D012996:Solutions; D002101:Cacodylic Acid; C020300:monomethylarsonic acid; D001151:Arsenic