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Abstract Processing bodies (PBs) and stress granules (SGs) are membrane-less cellular compartments consisting of ribonucleoprotein complexes. Whereas PBs are more ubiquitous, SGs are assembled mainly in response to stress. PBs and SGs are known to physically interact and molecules exchange between the two have been documented in mammals. However, the molecular mechanisms underpinning these processes are virtually unknown in plants. We have reported recently that tandem CCCH zinc finger 1 (TZF1) protein can recruit MAPK signaling components to SGs. Here we have found that TZF1-MPK3/6-MKK4/5 form a protein-protein interacting network in SGs. The mRNA decapping factor 1 (DCP1) is a core component of PBs. MAPK signaling mediated phosphorylation triggers a rapid reduction of DCP1 partition into PBs, concomitantly associated with an increase of DCP1 assembly into SGs. Furthermore, we have found that plant SG marker protein UBP1b (oligouridylate binding protein 1b) plays a role in maintaining DCP1 in PBs by suppressing the accumulation of MAPK signaling components. Together, we propose that MAPK signaling and UBP1b mediate the dynamics of PBs and SGs in plant cells. 

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 Sessile plants encode a large number of small peptides and cell surface-resident receptor kinases, most of which have unknown functions. Here, we report that theArabidopsisreceptor kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) recognizes the conserved signature motif of SERINE-RICH ENDOGENOUS PEPTIDEs (SCOOPs) fromBrassicaceaeplants as well as proteins present in fungalFusariumspp. and bacterialComamonadaceae, and elicits various immune responses. SCOOP signature peptides trigger immune responses and altered root development in a MIK2-dependent manner with a sub-nanomolar sensitivity. SCOOP12 directly binds to the extracellular leucine-rich repeat domain of MIK2 in vivo and in vitro, indicating that MIK2 is the receptor of SCOOP peptides. Perception of SCOOP peptides induces the association of MIK2 and the coreceptors SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3 (SERK3) and SERK4 and relays the signaling through the cytosolic receptor-like kinasesBOTRYTIS-INDUCED KINASE 1 (BIK1) and AVRPPHB SUSCEPTIBLE1 (PBS1)-LIKE 1 (PBL1). Our study identifies a plant receptor that bears a dual role in sensing the conserved peptide motif from phytocytokines and microbial proteins via a convergent signaling relay to ensure a robust immune response. 

We developed a new method for simultaneously visualizing RNAs and proteins in plant cells. This method works well for endogenous as well as infectious RNAs and their cognate binding proteins. 

Tandem CCCH zinc finger (TZF) proteins play diverse roles in plant growth and stress response. Although as many as 11 TZF proteins have been identified inArabidopsis, little is known about the mechanism by which TZF proteins select and regulate the target mRNAs. Here, we report thatArabidopsisTZF1 is a bona-fide stress granule protein. Ectopic expression ofTZF1(TZF1 OE), but not an mRNA binding-defective mutant (TZF1^H186YOE), enhances salt stress tolerance inArabidopsis. RNA-seq analyses of NaCl-treated plants revealed that the down-regulated genes inTZF1 OEplants are enriched for functions in salt and oxidative stress responses. Because many of these down-regulated mRNAs contain AU- and/or U-rich elements (AREs and/or UREs) in their 3’-UTRs, we hypothesized that TZF1—ARE/URE interaction might contribute to the observed gene expression changes. Results from RNA immunoprecipitation-quantitative PCR analysis, gel-shift, and mRNA half-life assays indicate that TZF1 binds and triggers degradation of theautoinhibited Ca²⁺-ATPase 11(ACA11) mRNA, which encodes a tonoplast-localized calcium pump that extrudes calcium and dampens signal transduction pathways necessary for salt stress tolerance. Furthermore, this salt stress-tolerance phenotype was recapitulated inaca11null mutants. Collectively, our findings demonstrate that TZF1 binds and initiates degradation of specific mRNAs to enhance salt stress tolerance.