RNA Interference-Mediated Repression of S6 Kinase 1 Impairs Root Nodule Development in Soybean

다국어 초록 (Multilingual Abstract)

Symbiotic nodule formation on legume roots is characterized with a series of developmental reprograming in root tissues, including extensive proliferation of cortical cells. We examined a possible involvement of the target of rapamycin (TOR) pathway, a central regulator of cell growth and proliferation in animals and yeasts, during soybean nodule development. Our results show that transcription of both GmTOR and its key downstream effector, GmS6K1, are activated during nodulation, which is paralleled with higher kinase activities of these gene products as well. RNAi-mediated knockdown of GmS6K1 impaired the nodule development with severely reduced nodule weight and numbers. In addition, expression of a few nodulins including leghemoglobin was also decreased, and consequently nitrogen fixation was found to be reduced by half. Proteomic analysis of the GmS6K1-RNAi nodules identified gluta-mine synthetase (GS), an essential enzyme for nitrogen assimilation in nodules, as one of the proteins that are significantly down regulated. These results appear to provide solid evidence for a functional link between GmS6K1 and nodule development.

참고문헌 (Reference)

1 Laplante, M, "mTOR signaling in growth control and disease" 149 : 274-293, 2012

2 Arsham, A., "Thinking globally and acting locally with TOR" 18 : 589-597, 2006

3 Oldroyd, G.E, "The rules of engagement in the legume-rhizobial symbiosis" 45 : 119-144, 2011

4 Cardenas, M.E., "The TOR signaling cascade regulates gene expression in response to nutrients" 13 : 3271-3279, 1999

5 Oh, H. S., "The Bradyrhizobium japonicum hsfA gene exhibits a unique developmental expression pattern in cowpea nodules" American Phytopathological Society 14 (14): 1286-1292, 2001

6 Ott, T, "Symbiotic leghemoglobins are crucial for nitrogen fixation in legume root nodules but not for general plant growth and development" 15 : 531-535, 2005

7 Cheatham, L, "Structural and functional analysis of pp70S6K" 92 : 11696-11700, 1995

8 Pende, M, "S6K1-/-S6K2-/- mice exhibit perinatal lethality and rapamycinsensitive5’- terminal oligopyrimidine mRNA translation and reveal a mitogen-activated protein kinase-dependent S6 kinase pathway" 24 : 3112-3124, 2004

9 Williams, A.J, "Regulated phosphorylation of 40S ribosomal protein S6 in root tips of maize" 132 : 2086-2097, 2003

10 Yun-jeong Shin, "Possible Dual Regulatory Circuits Involving AtS6K1 in the Regulation of Plant Cell Cycle and Growth" 한국분자세포생물학회 33 (33): 487-496, 2012

11 Turck, F, "Phytohormones participate in an S6 kinase signal transduction pathway in Arabidopsis" 134 : 1527-1535, 2004

12 Cheon, C.-I., "Nodulin-24 follows a novel pathway for integration into the peribacteroid membrane in soybean root nodules" 269 : 6598-6602, 1994

13 Weng, Q.-P, "Multiple independent inputs are required for activation of the p70 S6 kinase" 15 : 2333-2340, 1995

14 Ma, X.M., "Molecular mechanisms of mTORmediated translational control" 10 : 307-318, 2009

15 Masalkar, P, "Interaction of cytosolic glutamine synthetase of soybean root nodules with the C-terminal domain of the symbiosome membrane nodulin 26 aquaglyceroporin" 285 : 23880-23888, 2010

16 Lee, M. Y., "Induction of thioredoxin is required for nodule development to reduce reactive oxygen species levels in soybean roots" AMER SOC PLANT BIOLOGISTS 139 (139): 1881-1889, 2005

17 Krieg, J, "Identification of the 40S ribosomal protein S6 phosphorylation sites induced by cycloheximide" 263 : 11473-11477, 1988

18 Radimerski, T, "Identification of insulin-induced sites of ribosomal protein S6 phosphorylation in Drosophila melanogaster" 39 : 5766-5774, 2000

19 Menand, B, "Expression and disruption of the Arabidopsis TOR (target of rapamycin) gene" 99 : 6422-6427, 2002

20 Montagne, J, "Drosophila S6 kinase: a regulator of cell size" 285 : 2126-2129, 1999

21 Reuda-Lopéz, M, "Differential regulation of two glutamine synthetase genes by a single Dof transcription factor" 56 : 73-85, 2008

22 Lohar, D.P, "Cytokinins play opposite roles in lateral root formation, and nematode and Rhizobial symbioses" 38 : 203-214, 2004

23 Oldroyd, G.E, "Coordinating nodule morphogenesis with rhizobial infection in legumes" 59 : 519-546, 2008

24 Wesley, S.V, "Construct design for efficient, effective and highthroughput gene silencing in plants" 27 : 581-590, 2001

25 Mahfouz, M.M, "Arabidopsis TARGET OF RAPAMYCIN interacts with RAPTOR, which regulates the activity of S6 kinase in response to osmotic stress signals" 18 : 477-490, 2006

26 Henriques, R, "Arabidopsis S6 kinase mutants display chromosome instability and altered RBR1-E2F pathway activity" 29 : 2979-2993, 2010