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Root system responses to low temperature acclimation of Arabidopsis reil ribosome biogenesis double mutants

ABSTRACT: The REIL proteins are required for late ribosomal biogenesis and accumulation of the 60S large ribosome subunit in mature leaves of Arabidopsis thaliana upon acclimation to low temperature. To validate these functions in roots, we conducted a multi-level system analysis targeted at understanding defects and compensations responses of reil mutants before acclimation to low temperature and following temperature shift. Hydroponic root tissue enabled analysis of eukaryotic ribosome complexes with negligible interference of organelle ribosomes. Hydroponic cultivation attenuated the growth defect of reil mutants at low temperature and provided new insights into the primary functions of Arabidopsis REIL proteins. Arabidopsis tightly controls the balance of non-translating 40S and 60S subunits. Reil mutants initially deplete both non-translating subunits upon shift to 10°C and subsequently replenish these pools slowly. Reil mutations compensate the 60S biosynthesis defect by increased baseline levels of non-translating 40S and 60S subunits and depletion of a likely non-translating, KCl-sensitive 80S sub-fraction in the cold. We infer that Arabidopsis buffers fluctuating translation demands following temperature cues by activating non-translating ribosome fractions before de novo synthesis meets temperature-induced demands. Reil1 reil2 double mutants accumulate 43S-preinitiation complexes and pre-60S-maturation complexes and affect the paralog composition of non-translating ribosome fractions. With few exceptions, e.g. RPL3B and RPL24C, these changes were not under transcriptional control. Our study suggests requirement of de novo synthesis of eukaryotic ribosomes for long-term cold acclimation. Double mutant analysis indicates feedback control of REIL-mediated 60S maturation on NUC2 and eIF3C2 transcription and implies functions of two so far non-described proteins in late plant ribosome biogenesis. We propose that Arabidopsis requires biosynthesis of specialized ribosomes for successful cold acclimation.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE144916 | GEO | 2021/02/03

REPOSITORIES: GEO

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Project description:Functions of Arabidopsis REI1-LIKE (REIL) proteins, two homologs of a yeast ribosome biogenesis protein (RBP) that takes part in the late cytoplasmic steps of 60S ribosomal subunit maturation, were characterized by systems analyses of the 10°C cold acclimating reil1-1 reil2-1 double mutant compared to Col-0 wildtype. The mutant lacked both REIL proteins, was strongly growth inhibited in the cold and complemented by constitutive expression of N-terminal FLUORESCENT PROTEIN (FP)-REIL1 and FP-REIL2 fusion proteins under control of the UBIQUITIN 10 promoter. Wildtype acclimation to 10°C causes relative accumulation of cytosolic ribosome subunits and rRNA. Expression of cytosolic ribosomal genes, known cytosolic RBPs, translation initiation- and elongation-factors was activated. Conserved function of Arabidopsis REIL proteins was indicated by delay of these processes in reil1-1 reil2-1, cytosolic localization of FP-REIL proteins and native REIL protein interactions with 60S containing ribosome fractions. Non-acclimated reil1-1 reil2-1 triggered plant specific metabolic and transcriptomic cold acclimation responses that included activation of the DREB/CBF-regulon with a preference for the cold acclimation factors, CBF1/DREB1B, CBF2/DREB1C, and CBF3/DREB1A. Cold-acclimating reil1-1 reil2-1 maintained cellular integrity and acquired freezing tolerance but did not activate FLOWERING LOCUS T expression in mature leaves. This block was independent of FLOWERING LOCUS C and AGAMOUS-LIKE 19 mediated vernalization. We conclude that Arabidopsis REIL proteins enhance accumulation of cytosolic ribosome subunits after cold shift and either directly or indirectly feedback on temperature perception by suppression of premature cold acclimation at optimized temperature and by triggering growth and the vegetative to generative phase transition in the cold. Transcriptomic profiling demonstrated a hidden acclimation phenotype of the morphologically inconspicuous reil1-1reil2-1 mutant under optimized temperature conditions. Premature triggering of cold acclimation, a severe growth defect at 10°C and compensation responses indicate that REIL function may extend beyond cytosolic ribosome biogenesis towards translation initiation.

Project description:During cold acclimation plants increase their freezing tolerance in response to low non-freezing temperatures. This is accompanied by many physiological, biochemical and molecular changes that have been extensively investigated. In addition, many cold acclimated plants become more freezing tolerant during exposure to mild, non-damaging sub-zero temperatures. There is hardly any information available about the molecular basis of this adaptation. However, Arabidopsis thaliana is among the species that acclimate to sub-zero temperatures. This makes it possible to use the molecular and genetic tools available in this species to identify components of sub-zero signal transduction and acclimation. Here, we have used microarrays and a qRT-PCR primer platform covering 1880 genes encoding transcription factors to monitor changes in gene expression in the accessions Columbia-0, Rschew and Tenela during the first three days of sub-zero acclimation at -3°C. The results indicate that gene expression during sub-zero acclimation follows a tighly controlled time-course. Especially AP2/EREBP and WRKY transcription factors may be important regulators of sub-zero acclimation, although the CBF signal transduction pathway seems to be less important during sub-zero than during cold acclimation. Globally, we estimate that approximately 5% of all Arabidopsis genes are regulated during sub-zero acclimation. Particularly photosynthesis-related genes were down-regulated and genes belonging to the functional classes of cell wall biosynthesis, hormone metabolism and RNA regulation of transcription were up-regulated. Collectively, these data provide the first global analysis of gene expression during sub-zero acclimation and allow the identification of candidate genes for forward and reverse genetic studies into the molecular mechanisms of sub-zero acclimation. We used whole genome microarrays to monitor changes in gene expression in the Arabidopsis thaliana accessions Columbia-0, Rschew and Tenela during three days of acclimation to sub-zero temperature at -3°C after cold acclimation

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Root system responses to low temperature acclimation of Arabidopsis reil ribosome biogenesis double mutants

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