Regulation of gene expression through translational control is common in many organisms. The Arabidopsis (Arabidopsis thaliana) transcription factor bZIP11 is translational repressed in response to sucrose (Suc), resulting in Suc-regulated changes in amino acid metabolism. The 5# leader of the bZIP11 mRNA harbors several upstream open reading frames (uORFs), of which the second uORF is well conserved among bZIP11 homologous genes. The uORF2 element encodes a Suc control peptide (SC-peptide) of 28 residues that is sufficient for imposing Suc-induced repression of translation (SIRT) on a heterologous mRNA. Detailed analysis of the SC-peptide suggests that it functions as an attenuator peptide. Results suggest that the SCpeptide inhibits bZIP11 translation in response to high Suc levels by stalling the ribosome on the mRNA. The conserved noncanonical AUG contexts of bZIP11 uORFs allow inefficient translational initiation of the uORF, resulting in translation initiation of the scanning ribosome at the AUG codon of the bZIP11 main ORF. The results presented show that Suc-dependent signaling mediates differential translation of mRNAs containing SC-peptides encoding uORFs.

SignificanceFlooding due to extreme weather events can be highly detrimental to plant development and yield. Speedy recovery following stress removal is an important determinant of tolerance, yet mechanisms regulating this remain largely uncharacterized. We identified a regulatory network in Arabidopsis thaliana that controls water loss and senescence to influence recovery from prolonged submergence. Targeted control of the molecular mechanisms facilitating stress recovery identified here could potentially improve performance of crops in flood-prone areas.

Cytosolic ribosomes are among the largest multisubunit cellular complexes. Arabidopsis thaliana ribosomes consist of 79 different ribosomal proteins (r-proteins) that each are encoded by two to six (paralogous) genes. It is unknown whether the paralogs are incorporated into the ribosome and whether the relative incorporation of r-protein paralogs varies in response to environmental cues. Immunopurified ribosomes were isolated from A. thaliana rosette leaves fed with sucrose. Trypsin digested samples were analyzed by qTOF-LC-MS using both MS(E) and classical MS/MS. Peptide features obtained by using these two methods were identified using MASCOT and Proteinlynx Global Server searching the theoretical sequences of A. thaliana proteins. The A. thaliana genome encodes 237 r-proteins and 69% of these were identified with proteotypic peptides for most of the identified proteins. These r-proteins were identified with average protein sequence coverage of 32% observed by MS(E) . Interestingly, the analysis shows that the abundance of r-protein paralogs in the ribosome changes in response to sucrose feeding. This is particularly evident for paralogous RPS3aA, RPS5A, RPL8B, and RACK1 proteins. These results show that protein synthesis in the A. thaliana cytosol involves a heterogeneous ribosomal population. The implications of these findings in the regulation of translation are discussed.