Difference between revisions of "Os07g0150700"
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[[Category:Genes]] | [[Category:Genes]] | ||
[[Category:Japonica mRNA]] | [[Category:Japonica mRNA]] | ||
Latest revision as of 08:32, 12 June 2015
Os-AKT1, an inward K+ channel, is critical for K+ uptake in rice roots and is modulated by the rice CBL1-CIPK23 Complex. [1]
Contents
Annotated Information
Function
AKT1 is an important K+ channel and plays crucial roles in K+ uptake in Arabidopsis roots. The Arabidopsis akt1 mutant plants exhibit low-K+-sensitive phenotypes and a significant decrease in K+ content after growth on low-K+ medium [2][3] [4]. To examine the possible function of Os-AKT1, the coding sequence of Os-AKT1 was cloned and transformed into Arabidopsis akt1 mutant (ecotype Columbia [Col]) and two transgenic lines were obtained. The phenotype tests showed that the low-K+-sensitive phenotype of akt1 mutant was rescued in these two transgenic lines (akt1/Os-AKT1), which displayed a similar phenotype as wild-type (Col) plants. The K+ contents in these two transgenic lines were also rescued. Moreover, the root K+ content in these two lines were even higher than that in wild-type plants under low-K+ conditions. These results demonstrate that Os-AKT1 has similar function in K+ uptake as AKT1 in Arabidopsis. To measure the Os-AKT1-mediated K+ currents in Arabidopsis root cells, patch-clamp whole-cell recording was conducted using root cell protoplasts. Inward K+ currents were observed in root cell protoplasts of wild-type plants, but not in those of the akt1 mutant, suggesting that the inward K+ currents in wild-type root cells were contributed by AKT1 channel [2][5][4]. However, the akt1/Os-AKT1 transgenic line showed obvious inward K+ currents, suggesting that Os-AKT1 could mediate K+ uptake in Arabidopsis root cells. It should be noted that the Os-AKT1-mediated K+ currents were different from the currents conducted by Arabidopsis AKT1 channel. The half-activation voltage of Os-AKT1 (V1/2 = −173 ± 5 mV) was more negative than that of At-AKT1 (V1/2 = −133 ± 4 mV), suggesting that Os-AKT1 requires a more negative membrane potential to be activated.
Mutation
The T-DNA insertion mutant line of Os-AKT1 from RiceGE (Rice Functional Genomic Express Database, http://signal.salk.edu/cgi-bin/RiceGE) was used to validate the physiological function of Os-AKT1 in rice. In this Os-akt1 mutant, the T-DNA fragment is inserted into the 5′-untranslated region of Os-AKT1, 303 bp upstream of the start codon. The insertion leads to the knockdown of Os-AKT1 in the mutant plants compared with wild-type (O. sativa ssp japonica cv Dongjin) plants. The results of DNA gel blot assays indicated that there is only one copy of the T-DNA fragment inserting into the mutant plants.
Using hydroponic culture, the phenotype of Os-akt1 mutant and wild-type (Dongjin) plants was tested. The 14-d-old rice seedlings were transferred into normal (1 mM K+) and low K+ (100 μM K+) medium. After growth for 7 d, the Os-akt1 mutant seedlings showed overall growth inhibition compared with wild-type plants in both normal and low K+ conditions. In addition, the Os-akt1 mutant displayed the brown spots on old leaves, which was a typical K+-deficient symptom of rice. This symptom in Os-akt1 mutant became more remarkable under low K+ conditions. The K+ content of the Os-akt1 mutant was significantly reduced in both root and shoot compared with wild-type plants. Since Os-AKT1 is an inward K+ channel, this K+ deficiency in Os-akt1 might be due to the defect of Os-AKT1-mediated K+ uptake. The results of K+ depletion experiments [6] showed that the K+ uptake in Os-akt1 was obviously slower than that in the wild type. These results demonstrated that the loss of function of Os-AKT1 led to the reduction of K+ uptake in Os-akt1 mutants, which caused growth inhibition and K+-deficient symptoms in mutant plants. The function of Os-AKT1 was further confirmed using two complementation lines for the Os-akt1 mutant. The expression of Os-AKT1 in these two transgenic lines was recovered and the growth inhibition and K+-deficient symptoms were relieved.
The growth of Os-akt1 mutant plants was inhibited throughout development. The heading and grain-filling stages were delayed in Os-akt1. In addition, the lesion of Os-AKT1 also impaired grain yield. The grain number, seed set percentage, and 100-grain weight of the main panicle were all significantly reduced in Os-akt1.
Expression
To determine the expression profiles of Os-AKT1 in rice, transgenic rice plants carrying a GUS gene under control of an Os-AKT1 promoter fragment (1010 bp; O. sativa ssp japonica cv Nipponbare) were generated. The β-glucuronidase (GUS) activity assays showed that the Os-AKT1 promoter drives strong expression in roots and slight expression in shoots. In root tissues, GUS activity was observed in all cell types. The expression of Os-AKT1 in the epidermis and root hairs suggests a physiological role for Os-AKT1 in root K+ uptake from soil. Furthermore, GUS activity was also detected in cortex, endodermis, and vascular bundles, which indicates Os-AKT1 may also participate in K+ translocation in roots. In shoot tissues, Os-AKT1 promoter activity was mainly found in epidermis and vascular bundles.
Evolution
Os-AKT1 shares high similarity with other Shaker K+ channels from plant species, such as At-AKT1, Sl-LKT1, St-SKT1, Zm-ZMK1, Ta-AKT1, and Hv-AKT1 (58, 60, 60, 73, 76, and 75% identities, respectively). Phylogenetic analysis classified the K+ channels from monocots and dicots separatel. The Os-AKT1 P-loop domain contains a typical TxxTxGYG motif, a hallmark of K+-selective channels [7], suggesting that Os-AKT1 is likely to exhibit high ion selectivity for K+. The high degree of similarity of these Shaker K+ channels indicates that they likely have similar physiological functions in the different plant species.
Labs working on this gene
1. State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, National Plant Gene Research Centre (Beijing), China Agricultural University, Beijing 100193, China
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Juan Li;Yu Long;Guo-Ning Qi;Juan Li;Zi-Jian Xu;Wei-Hua Wu;Yi Wang. (2014) The Os-AKT1 Channel Is Critical for K+ Uptake in Rice Roots and Is Modulated by the Rice CBL1-CIPK23 Complex. The Plant Cell, 26(8): 3387-3402.
- ↑ 2.0 2.1 Hirsch R.E., Lewis B.D., Spalding E.P., Sussman M.R. (1998). A role for the AKT1 potassium channel in plant nutrition. Science 280: 918–921.
- ↑ Spalding E.P., Hirsch R.E., Lewis D.R., Qi Z., Sussman M.R., Lewis B.D. (1999). Potassium uptake supporting plant growth in the absence of AKT1 channel activity: Inhibition by ammonium and stimulation by sodium. J. Gen. Physiol. 113: 909–918.
- ↑ 4.0 4.1 Xu J., Li H.D., Chen L.Q., Wang Y., Liu L.L., He L., Wu W.H. (2006). A protein kinase, interacting with two calcineurin B-like proteins, regulates K+ transporter AKT1 in Arabidopsis. Cell 125: 1347–1360.
- ↑ Reintanz B., Szyroki A., Ivashikina N., Ache P., Godde M., Becker D., Palme K., Hedrich R. (2002). AtKC1, a silent Arabidopsis potassium channel α-subunit modulates root hair K+ influx. Proc. Natl. Acad. Sci. USA 99: 4079–4084.
- ↑ Drew M.C., Saker L.R., Barber S.A., Jenkins W. (1984). Changes in the kinetics of phosphate and potassium absorption in nutrient-deficient barley roots measured by a solution-depletion technique. Planta 160: 490–499.
- ↑ Doyle D.A., Morais Cabral J., Pfuetzner R.A., Kuo A., Gulbis J.M., Cohen S.L., Chait B.T., MacKinnon R. (1998). The structure of the potassium channel: molecular basis of K+ conduction and selectivity. Science 280: 69–77.
