Abstract
Heat stress in plant results in repression of most mRNA translation and the preferential translation of heat shock protein (hsp) mRNAs. 5' untranslated regions (5'-UTR) of hsp mRNAs are known to confer the preferential translation during heat stress. In this study, we showed that the m7G-capped reporter mRNA with 5'-UTR of Arabidopsis hsp90 gene was translated efficiently during heat stress by using Arabidopsis T87 protoplast transient expression assay. To investigate the function of the hsp90 5'-UTR in more detail, we performed the same transient expression assay using uncapped monocistronic reporter mRNA or capped bicistronic mRNA. As a result, hsp90 5'-UTR conferred temperature dependent increase in the expression from uncapped monocistronic mRNA and from second cistron of bicistronic mRNA. These data suggest that cap-independent translation via internal ribosome entry site (IRES) in hsp90 5'-UTR contributes the efficient translation of hsp90 during heat stress, which inhibits cap-dependent translation.
