Regulation of Translation Initiation under Abiotic Stress Conditions in Plants: Is It a Conserved or Not so Conserved Process among Eukaryotes?

Figure 1

Regulation of translational initiation factors and transcript-differential translation under abiotic stress conditions. (a) Protein synthesis inhibition has been observed upon eIF2α phosphorylation both in plants and in other eukaryotes subjected to different abiotic stress conditions. In plants (right panel), in contrast to vertebrates (the case illustrated) (left panel), only the eIF2α kinase GCN2 has been described. In yeast and mammals eIF2α phosphorylation mediated by GCN2 promotes the selective translation of some mRNAs as GCN4 or ATF4, respectively; however, whether eIF2α phosphorylation leads to the stimulation of translation of specific mRNAs is unknown in plants. (b) In mammals the activity of eIF4E under abiotic stress is regulated by the eIF4E binding to hypophosphorylated forms of the 4E-BPs (left panel). Such binding promotes cap-dependent translation inhibition and the observation of cap-independent translation. Different evidences point out that plants can support cap-independent translation under abiotic stress conditions (right panel). However, the role of eIF4E and TOR in this process has to be elucidated. (c) Some abiotic stress conditions promote the selective translation of mRNAs with low G+C content in yeast and plants. In yeast (left panel) the involvement of eIF4A in this regulation has been described, although the exact mechanism regulating the activity of eIF4A is still unclear. In plants (right panel) the role of eIF4A in this process has to be determined.