Abstract
Plants are constantly exposed to environmental stresses, including biotic and abiotic stresses, all of which give occasionally serious damages to their survival. To cope with these stresses, plants have evolved various functional proteins by fitness. This study focuses on protein evolution by analyzing the mechanism of localization change from nucleus to plastids. A wound- and pathogen-responsive bHLH protein, NtWIN4, was previously identified in chloroplasts of tobacco leaves. Since bHLH proteins are generally known to function as nuclear transcription factor, NtWIN4 was conceivably converted from nucleus-residence to plastid-specific protein during evolution, resulting in participation in hypersensitive response through chlorosis. Plastid-resident NtWIN4 was predicted to be synthesized from the in-frame second AUG. In fact, further analysis identified short mRNAs lacking the first AUG, from which plastid-type polypeptide was translated in vitro. Results suggested that the different size of mRNAs is one of factors that induce localization change of NtWIN4.
