PHOSPHORYLATION OF TOBACCO EUKARYOTIC TRANSLATION INITIATION-FACTOR 4A UPON POLLEN-TUBE GERMINATION

Eukaryotic translation initiation factor eIF-4A is a member of the DEA D box family of RNA helicases and RNA-dependent ATPases, In tobacco, e IF-4A is encoded by a gene family with one isoform, eIF-4A8, being exc lusively expressed in pollen. This pollen-specific isoform is a candid ate for mediating translational control in the developing gametophyte. Here we show that eIF-4A is barely phosphorylated in mature pollen, b ut during pollen tube germination, two isoforms of eIF-4A become phosp horylated. Phosphoamino acid analysis indicated phosphorylation of thr eonine. In order to determine whether pollen-specific eIF-4A8 is among the phosphorylated isoforms, we raised transgenic tobacco plants over expressing eIF-4A8 containing a histidine tag. Hereby, we could show t hat indeed eIF-4A8 is modified through phosphorylation. The biological relevance of the phosphorylation of eIF-4A is discussed.