THE ARABIDOPSIS-THALIANA CDNAS CODING FOR EIF4E AND EIF(ISO)4E ARE NOT FUNCTIONALLY EQUIVALENT FOR YEAST COMPLEMENTATION AND ARE DIFFERENTIALLY EXPRESSED DURING PLANT DEVELOPMENT

Two cDNAs (At.EIF4E1 and At.EIF4E2) encoding, respectively, the eukary otic initiation factors elF4E and elF(iso)4E of Arabidopsis thaliana w ere isolated by complementation of a Saccharomyces cerevisiae conditio nal mutant. The deduced amino acid sequences of the proteins are homol ogous to those from monocotyledonous plants, yeast and mammals. The co rresponding genes were identified in YAC clones mapping to chromosome IV (At.EIF4E1) and to chromosome V (At.EIF4E2). The yeast strain compl emented by At.EIF4E2 grew poorly compared with an isogenic strain expr essing At.EIF4E1. Northern and in situ hybridization analysis show tha t both Arabidopsis At.EIF4E1 and At.EIF4E2 mRNAs are differentially ac cumulated in plant tissues. The At.EIF4E1 mRNA is expressed in all tis sues except in the cells of the specialization zone of the roots; the At.EIF4E2 mRNA is particularly abundant in floral organs and in young developing tissues. This work further demonstrates an association betw een a high level of EIF4E mRNAs and cell proliferation and suggests th at the plant elF4E isoforms may have distinct functions in cell develo pment and metabolism.