Ribosomal Protein S6, a target of TOR, is involved in the regulation of rRNA genes by possible epigenetic changes in Arabidopsis [Signal Transduction]

December 3rd, 2013 by Kim, Y.-K., Kim, S., Shin, Y.-j., Kim, W.-Y., Lee, M.-S., Cheon, C.-I., Verma, D. P. S.

TOR (Target Of Rapamycin) kinase pathway regulates various biological processes including translation, synthesis of ribosomal proteins, and transcription of rRNA. The ribosomal protein S6 (RPS6) is one of the well-known downstream components of the TOR pathway. Ribosomal proteins have been known to have diverse functions in regulating cellular metabolism as well as protein synthesis. However, so far, little is known about other possible role(s) of RPS6 in plants, besides being a component of the 40S ribosomal subunit and acting as a target of TOR. Here, we report that RPS6 may have a novel function via interaction with the histone deacetylase 2B (AtHD2B) that belongs to the plant-specific histone deacetylase HD2 family. RPS6 and AtHD2B were localized to the nucleolus. Co-expression of RPS6 and AtHD2B caused a change in the location of both RPS6 and AtHD2B to one or several nucleolar spots. ChIP analysis suggests that RPS6 directly interacts with the rRNA gene promoter. Protoplasts overexpressing both AtHD2B and RPS6 exhibited down-regulation of pre- 18S rRNA synthesis with concomitant decrease in some of the ribosomal proteins transcription, suggesting their direct role in ribosome biogenesis and plant development. This is consistent with the mutation in rps6b that results in reduction in 18S rRNA transcription and decreased root growth. We propose that the interaction between RPS6 and AtHD2B brings about a change in the chromatin structure of rDNA and thus plays an important role in linking TOR signaling to rDNA transcription and ribosome biogenesis in plants.
  • Posted in Journal of Biological Chemistry, Publications
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