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ABSTRACT Viroids are single‐stranded circular noncoding RNAs that mainly infect crops. Upon infection, nuclear‐replicating viroids engage host DNA‐dependent RNA polymerase II for RNA‐templated transcription, which is facilitated by a host protein TFIIIA‐7ZF. The sense‐strand and minus‐strand RNA intermediates are differentially localised to the nucleolus and nucleoplasm regions, respectively. The factors and function underlying the differential localisation of viroid RNAs have not been fully elucidated. The sense‐strand RNA intermediates are cleaved into linear monomers by a yet‐to‐be‐identified RNase III‐type enzyme and ligated to form circular RNA progeny by DNA ligase I (LIG1). The subcellular compartment for the ligation reaction has not been characterised. Here, we show that LIG1 and potato spindle tuber viroid (PSTVd) colocalise near the nucleolar region inNicotiana benthamianaprotoplasts. The colocalised region is also the highly condensed region of sense‐strand PSTVd RNA, indicating that PSTVd RNA and LIG1 form a biomolecular condensate for RNA processing. This finding expands the function of biomolecular condensates to the infection of subviral pathogens. In addition, this knowledge of viroid biogenesis will contribute to exploring thousands of viroid‐like RNAs that have been recently identified. 

Abstract Aphids represent a major threat to crops. Hundreds of different viruses are aphid-borne. Upon aphid attack, plants release volatile organic compounds (VOCs) as airborne alarm signals to turn on the airborne defense (AD) of neighboring plants, thereby repelling aphids as well as reducing aphid fitness and virus transmission. This phenomenon provides a critical community-wide plant protection to fend off aphids, but the underlying molecular basis remains undetermined for a long time. In a recent article, Gong et al. established theNAC2-SAMT1module as the core component regulating the emission of methyl-salicylate (MeSA), a major component of VOCs in aphid-attacked plants. Furthermore, they showed that SABP2 protein is critical for the perception of volatile MeSA signal by converting MeSA to Salicylic Acid (SA), which is the cue to elicit AD against aphids at the community level. Moreover, they showed that multiple viruses use a conserved glycine residue in the ATP-dependent helicase domain in viral proteins to shuttle NAC2 from the nucleus to the cytoplasm for degradation, leading to the attenuation of MeSA emission and AD. These findings illuminate the functional roles of key regulators in the complex MeSA-mediated airborne defense process and a counter-defense mechanism used by viruses, which has profound significance in advancing the knowledge of plant-pathogen interactions as well as providing potential targets for gene editing-based crop breeding.