Mutations in eIF5B Confer Thermosensitive and Pleiotropic Phenotypes via Translation Defects in .

The conserved eukaryotic translation initiation factor 5B, eIF5B, is a GTPase that acts late in translation initiation. We found that an mutant sensitive to temperatures 3 (), which behaves as the wild type in the absence of stress but is unable to acclimate to high temperature, carries a missense mutation in the gene (At1g76810), producing a temperature sensitive protein. A more severe, T-DNA insertion allele () causes pleiotropic developmental phenotypes. Surprisingly, Arabidopsis has three other genes that do not substitute for ; two of these appear to be in the process of pseudogenization. Polysome profiling and RNA-seq analysis of plants show delayed recovery of polysomes after heat stress and reduced translational efficiency (TE) of a subset of stress protective proteins, demonstrating the critical role of translational control early in heat acclimation. Plants carrying the severe allele show decreased TE of auxin-regulated, ribosome-related, and electron transport genes, even under optimal growth conditions. The data suggest that disrupting specific eIF5B interactions on the ribosome can, directly or indirectly, differentially affect translation. Thus, modulating eIF5B interactions could be another mechanism of gene-specific translational control.