Toward Resistance to Maize Lethal Necrosis Disease by Disruption of Cap-Independent Translation of Maize Chlorotic Mottle Virus RNA

Maize lethal necrosis disease (MLND), which recently invaded East Africa with devastating consequences, is caused by mixed infection of maize chlorotic mottle virus (MCMV) and a potyvirus, usually sugarcane mosaic virus. To address the lack of resistance to MCMV, we are targeting a weak link in infection: translation of viral RNA, which is required before virus replication. We found that, like all viruses in the Tombusviridae family, MCMV RNA lacks the 5’ cap required for translation of host mRNAs, and instead harbors a cap-independent translation element (CITE) in the 3’ untranslated region (UTR). We have mapped the MCMV CITE (MTE) to a ~100 nt sequence in the 3’ UTR that strongly stimulates translation of uncapped viral or luciferase reporter mRNA in wheat germ extract and in oat protoplasts. SHAPE probing revealed the MTE as a branched stem-loop structure with a bulge, somewhat resembling the panicum mosaic virus class of 3’ CITE (PTE), but without conserved bases that define PTEs. Despite lacking a cap, the MTE (like the PTE) binds the cap-binding translation initiation factor eIF4E with high affinity. We now seek to identify mutations in eIF4E that disrupt binding to the MTE but not to capped RNA. This should allow engineering (or screening for) resistance to MCMV by using a mutant eIF4E that functions normally with capped mRNA, but does not bind MCMV RNA, thus preventing viral RNA translation and the ensuing infection. This approach is promising, as natural mutations in eIF4E confer resistance to many other plant viruses.