Abstract
Light triggers an enhancement of global translation during photomorphogenesis in Arabidopsis, but little is known about the underlying mechanisms. The phosphorylation of the α-subunit of eukaryotic initiation factor 2 (eIF2α) at a conserved serine residue in the N-terminus has been shown as an important mechanism for the regulation of protein synthesis in mammalian and yeast cells. However, whether the phosphorylation of this residue in plant eIF2α plays a role in regulation of translation remains elusive. Here, we show that the quadruple mutant of SUPPRESSOR OF PHYA-105 family members (SPA1-SPA4) display repressed translation efficiency after light illumination. Moreover, SPA1 directly phosphorylates the eIF2α C-terminus under light conditions. The C-term-phosphorylated eIF2α promotes translation efficiency and photomorphogenesis, whereas the C-term-unphosphorylated eIF2α results in a decreased translation efficiency. We also demonstrate that the phosphorylated eIF2α enhances ternary complex assembly by promoting its affinity to eIF2β and eIF2γ. This study reveals a unique mechanism by which light promotes translation via SPA1-mediated phosphorylation of the C-terminus of eIF2α in plants.