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Plant and Cell Physiology Advance Access originally published online on August 3, 2009
Plant and Cell Physiology 2009 50(9):1695-1709; doi:10.1093/pcp/pcp114
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Overexpression of the Lily p70s6k Gene in Arabidopsis Affects Elongation of Flower Organs and Indicates TOR-Dependent Regulation of AP3, PI and SUP Translation

Tsai-Yu Tzeng1,2, Lih-Ren Kong1, Chun-Hung Chen1, Chih-Chi Shaw1 and Chang-Hsien Yang1,*

1Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan 40227 ROC

*Corresponding author: E-mail, chyang{at}dragon.nchu.edu.tw; Fax, +-886-4-2285-3126/+886-4-2285-3527.


  Abstract

The p70 ribosomal S6 kinase (p70s6k) signaling pathway plays a key role in regulating the cell cycle via translational regulation of specific 5'TOP mRNAs. However, the function of this signaling pathway is still poorly understood in plants. Ectopic expression of the lily putative p70s6k gene, LS6K1, resulted in up-regulation of NAP (NAC-LIKE, ACTIVATED BY AP3/PI) and PISTILLATA (PI) expression, and significantly inhibited cell expansion for petals and stamens, resulting in the male sterility phenotype in transgenic Arabidopsis. Sequence analysis revealed that the genes involved in petal and stamen development, such as APETALA3 (AP3), PI and SUPERMAN (SUP), probably encode 5'TOP mRNAs. Green fluorescent protein (GFP), fused to oligopyrimidine tract sequences that were identified in the 5'-untranslated region (UTR) of AP3, PI and SUP, was translationally regulated in human cells in response to mitogen stimulation and inhibition by the macrolide antibiotic rapamycin. Furthermore, 35S::LS6K1 significantly up-regulated β-glucuronidase (GUS) activity in the flower buds of transgenic plants carrying the GUS transgene fused to the AP3 promoter and the 5' UTR. These results have identified a novel role for the p70s6k gene in regulating cell division and the expansion of petals and stamens by translational regulation of the 5'TOP mRNAs once ectopically expressed in Arabidopsis.

Keywords: APETALA3 - Arabidopsis thaliana - Lilium longiflorum - p70 ribosomal S6 kinase - Translational control - 5'TOP mRNAs

Abbreviations: AP3, APETALA3; CaMV, cauliflower mosaic virus; CMV, cytomegalovirus; FBS, fetal bovine serum; GFP, green fluorescent protein; GUS, β-glucuronidase; ORF, open reading frame; NAP NAC-LIKE, ACTIVATED BY AP3/PI; PI, PISTILLATA; RACE, rapid amplification of cDNA ends; RAPTOR, Regulatory-Associated Protein of TOR; RT–PCR, reverse transcription–PCR; SEP, SEPALLATA; SUP, SUPERMAN; TOR, target of rapamycin; UTR, untranslated region

2Present address: Genome Research Center, National Yang-Ming University, Taipei, Taiwan, ROC.

(Received July 22, 2009; Accepted July 27, 2009)
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