The phosphorylation state of the wheat translation initiation factors eIF4B, eIF4A, and eIF2 is differentially regulated during seed development and germination

Abstract

The translation initiation factors (eIF) 4B and eIF2 are phosphoproteins whose phosphorylation state differs between mature seed and leaves. We examined the isoforms of eIF4B and the α and β subunits of eIF2 during the development and germination of wheat seed to determine whether the differences in their phosphorylation state are because of tissue-specific regulation or occur concomitant with changes in protein synthetic activity during development. eIF2α underwent phosphorylation through several intermediate isoforms that correlated with the increase and subsequent reduction in protein synthetic activity characteristic of seed development. eIF2β and eIF4B, present as highly phosphorylated isoforms during early seed development, underwent dephosphorylation during late development. eIF4B was rapidly phosphorylated within 20 h of germination, whereas eIF2α did not undergo dephosphorylation until 48-60 h of growth. A third factor, eIF4A, was predominantly nonphosphorylated throughout most of seed development and germination. These observations suggest that the phosphorylation state of eIF2α, eIF2β, and eIF4B is developmentally regulated in a way that correlates with the changes in protein synthetic activity but that some differences were also observed.