Dynamic control of protein translation in response to the environment is essential for the survival of plant cells. Target of rapamycin (TOR) coordinates protein synthesis with cellular energy/nutrient availability through transcriptional modulation and phosphorylation of the translation machinery. However, mechanisms of TOR-mediated translation control are poorly understood in plants. Here, we report that Arabidopsis thaliana MRF (MA3 DOMAIN-CONTAINING TRANSLATION REGULATORY FACTOR) family genes encode translation regulatory factors under TOR control, and their functions are particularly important in energy-deficient conditions. Four MRF family genes (MRF1-MRF4) are transcriptionally induced by dark and starvation (DS). Silencing of multiple MRFs increases susceptibility to DS and treatment with a TOR inhibitor, while MRF1 overexpression decreases susceptibility. MRF proteins interact with eIF4A and cofractionate with ribosomes. MRF silencing decreases translation activity, while MRF1 overexpression increases it, accompanied by altered ribosome patterns, particularly in DS. Furthermore, MRF deficiency in DS causes altered distribution of mRNAs in sucrose gradient fractions and accelerates rRNA degradation. MRF1 is phosphorylated in vivo and phosphorylated by S6 kinases in vitro. MRF expression and MRF1 ribosome association and phosphorylation are modulated by cellular energy status and TOR activity. We discuss possible mechanisms of the function of MRF family proteins under normal and energy-deficient conditions and their functional link with the TOR pathway.
Bibliographical noteFunding Information:
We thank Masayori Inouye (Rutgers University) and Sangita Phadtare (Rowan University) for providing the E. coli BX04 mutant strain and pINIII vector, Jen Sheen (Harvard Medical School) for providing seeds of the estradiol-inducible TOR RNAi lines, Detlef Weigel (Max Planck Institute for Developmental Biology, Germany) for the pRS300 vector, and Hunseung Kang (Chonnam National University, Korea) for helpful discussions. This research was supported by the Rural Development Administration (RDA) Cooperative Research Program for Agriculture Science and Technology Development (project numbers PJ01114701 [PMBC] and PJ01118901 [SSAC]) and the National Research Foundation of Korea (NRF) Mid-Career Researcher Program (NRF-2016R1A2B4013180).
© American Society of Plant Biologists.
All Science Journal Classification (ASJC) codes
- Plant Science
- Cell Biology