Abscisic Acid Connects Phytohormone Signaling with RNA Metabolic Pathways and Promotes an Antiviral Response that Is Evaded by a Self- Controlled RNA Virus

A complex network of cellular receptors,RNA targeting pathways,and small-molecule signaling provides robust plant immunity and tolerance to viruses.To maximize their fitness,viruses must evolve control mechanisms to balance host immune evasion and plant-damaging effects.The genus Potyvirus comprises plant viruses characterized by RNA genomes that encode large polyproteins led by the P1 protease.A P1 autoinhibitory domain controls polyprotein processing,the release of a downstream functional RNAsilencing suppressor,and viral replication.Here,we show that P1Pro,a plum pox virus clone that lacks the P1 autoinhibitory domain,triggers complex reprogramming of the host transcriptome and high levels of abscisic acid(ABA)accumulation.A meta-analysis highlighted ABA connections with host pathways known to control RNA stability,turnover,maturation,and translation.Transcriptomic changes triggered by P1Pro infection or ABA showed similarities in host RNA abundance and diversity.Genetic and hormone treatment assays showed that ABA promotes plant resistance to potyviral infection.Finally,quantitative mathematical modeling of viral replication in the presence of defense pathways supported self-control of polyprotein processing kinetics as a viral mechanism that attenuates the magnitude of the host antiviral response.Overall,our findings indicate that ABA is an active player in plant antiviral immunity,which is nonetheless evaded by a self-controlled RNA virus.

Engineering a Circular Riboregulator in Escherichia coli

RNAs of different shapes and sizes,natural or synthetic,can regulate gene expression in prokaryotes and eukaryotes.Circular RNAs have recently appeared to be more widespread than previously thought,but their role in prokaryotes remains elusive.Here,by inserting a riboregulatory sequence within a group I permuted intron-exon ribozyme,we created a small noncoding RNA that self-splices to produce a circular riboregulator in Escherichia coli.We showed that the resulting riboregulator can trans-activate gene expression by interacting with a cis-repressed messenger RNA.We characterized the system with a fluorescent reporter and with an antibiotic resistance marker,and we modeled this novel posttranscriptional mechanism.This first reported example of a circular RNA regulating gene expression in E.coli adds to an increasing repertoire of RNA synthetic biology parts,and it highlights that topological molecules can play a role in the case of prokaryotic regulation.