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Mol. Cells 2012; 33(5): 487-496

Published online May 31, 2012

https://doi.org/10.1007/s10059-012-2275-4

© The Korean Society for Molecular and Cellular Biology

Possible Dual Regulatory Circuits Involving AtS6K1 in the Regulation of Plant Cell Cycle and Growth

Yun-jeong Shin1,3, Sunghan Kim1,3, Hui Du1, Soonyoung Choi1, Desh Pal S. Verma2,*, and Choong-Ill Cheon1,*

1Department of Biological Science, Sookmyung Women’s University, Seoul 140-742, Korea, 2Department of Molecular Genetics and Plant Biotechnology Center, The Ohio State University, Columbus, Ohio 43210, USA, 3These authors contributed equally to this work.

Correspondence to : *Correspondence: ccheon@sookmyung.ac.kr (CIC); verma.1@osu.edu (DPSV)

Received: December 5, 2011; Revised: February 29, 2012; Accepted: March 2, 2012

Abstract

The role of Arabidopsis S6 Kinase 1 (AtS6K1), a down-stream target of TOR kinase, in controlling plant growth and ribosome biogenesis was characterized after generating transgenic plants expressing AtS6K1 under auxin-inducible promoter. Down-regulation of selected cell cycle regulatory genes upon auxin treatment was observed in the transgenic plants, confirming the negative regulatory role of AtS6K1 in the plant cell cycle progression reported earlier. Callus tissues established from these transgenic plants grew to larger cell masses with more number of enlarged cells than untransformed control, demonstrating functional implication of AtS6K1 in the control of plant cell size. The observed negative correlation between the expression of AtS6K1 and the cell cycle regulatory genes, however, was completely reversed in protoplasts generated from the transgenic plants expressing AtS6K1, suggesting a possible existence of dual regulatory mechanism of the plant cell cycle regulation mediated by AtS6K1. An alternative method of kinase assay, termed “substrate-mediated kinase pull down”, was employed to examine the additional phosphorylation on other domains of AtS6K1 and verified the phosphorylation of both amino- and carboxy-terminal domains, which is a novel finding regarding the phosphorylation target sites on plant S6Ks by upstream regulatory kinases. In addition, this kinase assay under the stress conditions revealed the salt- and sugar-dependencies of AtS6K1 phosphorylations.

Keywords AtS6K1, auxin, phosphorylation, plant cell growth, TOR

Article

Research Article

Mol. Cells 2012; 33(5): 487-496

Published online May 31, 2012 https://doi.org/10.1007/s10059-012-2275-4

Copyright © The Korean Society for Molecular and Cellular Biology.

Possible Dual Regulatory Circuits Involving AtS6K1 in the Regulation of Plant Cell Cycle and Growth

Yun-jeong Shin1,3, Sunghan Kim1,3, Hui Du1, Soonyoung Choi1, Desh Pal S. Verma2,*, and Choong-Ill Cheon1,*

1Department of Biological Science, Sookmyung Women’s University, Seoul 140-742, Korea, 2Department of Molecular Genetics and Plant Biotechnology Center, The Ohio State University, Columbus, Ohio 43210, USA, 3These authors contributed equally to this work.

Correspondence to:*Correspondence: ccheon@sookmyung.ac.kr (CIC); verma.1@osu.edu (DPSV)

Received: December 5, 2011; Revised: February 29, 2012; Accepted: March 2, 2012

Abstract

The role of Arabidopsis S6 Kinase 1 (AtS6K1), a down-stream target of TOR kinase, in controlling plant growth and ribosome biogenesis was characterized after generating transgenic plants expressing AtS6K1 under auxin-inducible promoter. Down-regulation of selected cell cycle regulatory genes upon auxin treatment was observed in the transgenic plants, confirming the negative regulatory role of AtS6K1 in the plant cell cycle progression reported earlier. Callus tissues established from these transgenic plants grew to larger cell masses with more number of enlarged cells than untransformed control, demonstrating functional implication of AtS6K1 in the control of plant cell size. The observed negative correlation between the expression of AtS6K1 and the cell cycle regulatory genes, however, was completely reversed in protoplasts generated from the transgenic plants expressing AtS6K1, suggesting a possible existence of dual regulatory mechanism of the plant cell cycle regulation mediated by AtS6K1. An alternative method of kinase assay, termed “substrate-mediated kinase pull down”, was employed to examine the additional phosphorylation on other domains of AtS6K1 and verified the phosphorylation of both amino- and carboxy-terminal domains, which is a novel finding regarding the phosphorylation target sites on plant S6Ks by upstream regulatory kinases. In addition, this kinase assay under the stress conditions revealed the salt- and sugar-dependencies of AtS6K1 phosphorylations.

Keywords: AtS6K1, auxin, phosphorylation, plant cell growth, TOR

Mol. Cells
Sep 30, 2022 Vol.45 No.9, pp. 603~672
COVER PICTURE
The Target of Rapamycin Complex (TORC) is a central regulatory hub in eukaryotes, which is well conserved in diverse plant species, including tomato (Solanum lycopersicum). Inhibition of TORC genes (SlTOR, SlLST8, and SlRAPTOR) by VIGS (virus-induced gene silencing) results in early fruit ripening in tomato. The red/ orange tomatoes are early-ripened TORC-silenced fruits, while the green tomato is a control fruit. Top, left, control fruit (TRV2-myc); top, right, TRV2-SlLST8; bottom, left, TRV2-SlTOR; bottom, right, TRV2-SlRAPTOR(Choi et al., pp. 660-672).

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