A critical review of translation initiation factor eIF2a kinases in plants – regulating protein synthesis during stress

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Abstract
Eukaryotic cells must cope with environmental stress. One type of general stress response is the downregulation of protein synthesis in order to conserve cellular resources. Protein synthesis is mainly regulated at the level of mRNA translation initiation and when the a subunit of eukaryotic translation initiation factor 2 (eIF2) is phosphorylated, protein synthesis is downregulated. Although eIF2 has the same translation initiation function in all eukaryotes, it is not known whether plants downregulate protein synthesis via eIF2a phosphorylation. Similarly, although there is evidence that plants possess eIF2a kinases, it is not known whether they operate in a similar manner to the well characterised mammalian and yeast eIF2a kinases. Two types of eIF2a kinases have been reported in plants, yet the full understanding of the plant eIF2a phosphorylation mechanism is still lacking. Here we review the current knowledge of the eIF2a phosphorylation mechanism within plants and discuss plant eIF2a, plant eIF2a kinase GCN2 and the data supporting and contradicting the hypothesis that a functional orthologue for the eIF2a kinase PKR, is present and functional in plants.

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