Abstract
The eukaryotic translation initiation factor (eIF) 4G is a scaffold protein that organizes the assembly of those initiation factors needed to recruit the 40 S ribosomal subunit to an mRNA. Plants, like many eukaryotes, express two eIF4G isoforms. eIFiso4G, one of the isoforms specific to plants, is unique among eukaryotic eIF4G proteins in that it is highly divergent and unusually small in size, raising the possibility of functional specialization. In this study, the role of eIFiso4G in plant growth was investigated using null mutants for the eIF4G isoforms in Arabidopsis. eIFiso4G loss of function mutants exhibited smaller cell, leaf, plant size, and biomass accumulation that correlated with its reduced photosynthetic activity, phenotypes not observed with the eIF4G loss of function mutant. Although no change in photorespiration or dark respiration was observed in the eIFiso4G loss of function mutant, a reduction in chlorophyll levels and an increase in the level of nonphotochemical quenching were observed. An increase in xanthophyll cycle activity and the generation of reactive oxygen species contributed to the qE and qI components of nonphotochemical quenching, respectively. An increase in the transcript and protein levels of violaxanthin de-epoxidase in the eIFiso4G loss of function mutant and an increase in its xanthophyll de-epoxidation state correlated with the higher qE associated with loss of eIFiso4G expression. These observations indicate that eIFiso4G expression is required to regulate violaxanthin de-epoxidase expression and to support photosynthetic activity.
Highlights
The initiation factor eIFiso4G organizes the assembly of those factors needed to initiate translation of plant mRNAs
These results indicate that loss of eIFiso4G expression affects the appropriate regulation of violaxanthin deepoxidase (VDE) expression, which is not affected by loss of eIF4G expression, and that eIFiso4G expression is important to maintain photosynthetic activity
We have examined the effect that loss of eIFiso4G expression has on VDE expression and, on photosynthetic performance
Summary
The initiation factor eIFiso4G organizes the assembly of those factors needed to initiate translation of plant mRNAs. An increase in the transcript and protein levels of violaxanthin de-epoxidase in the eIFiso4G loss of function mutant and an increase in its xanthophyll de-epoxidation state correlated with the higher qE associated with loss of eIFiso4G expression These observations indicate that eIFiso4G expression is required to regulate violaxanthin de-epoxidase expression and to support photosynthetic activity. In Arabidopsis, eIF4G is encoded by a single gene (i.e. At3g60240), whereas eIFiso4G is encoded by two genes, eIFiso4G1 and eIFiso4G2 (i.e. At5g57870 and At2g24050, respectively) [28] Given their role in supporting protein synthesis, loss of a general translational initiation factor might be expected to result in pleiotropic effects or lethality. The increase in VDE activity was a result of its greater expression in the eIFiso4G loss of function mutant, which was reflected at the transcript and protein levels. These results indicate that loss of eIFiso4G expression affects the appropriate regulation of VDE expression, which is not affected by loss of eIF4G expression, and that eIFiso4G expression is important to maintain photosynthetic activity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
