The transcriptional regulator JAZ8 interacts with the C2 protein from geminiviruses and limits the geminiviral infection in Arabidopsis

Jasmonates(JAs) are phytohormones that finely regulate critical biological processes, including plant development and defense. JASMONATE ZIM-DOMAIN(JAZ) proteins are crucial transcriptional regulators that keep JA-responsive genes in a repressed state. In the presence of JA-Ile, JAZ repressors are ubiquitinated and targeted for degradation by the ubiquitin/proteasome system,allowing the activation of downstream transcription factors and, consequently, the induction of JA-responsive genes. A growing body of evidence has shown that JA signaling is crucial in defending against plant viruses and their insect vectors. Here, we describe the interaction of C2proteins from two tomato-infecting geminiviruses from the genus Begomovirus, tomato yellow leaf curl virus(TYLCV) and tomato yellow curl Sardinia virus(TYLCSaV), with the transcriptional repressor JAZ8 from Arabidopsis thaliana and its closest orthologue in tomato, SlJAZ9. Both JAZ and C2proteins colocalize in the nucleus, forming discrete nuclear speckles. Overexpression of JAZ8did not lead to altered responses to TYLCV infection in Arabidopsis;however, knock-down of JAZ8 favors geminiviral infection. Low levels of JAZ8 likely affect the viral infection specifically,since JAZ8-silenced plants neither display obvious developmental phenotypes nor present differences in their interaction with the viral insect vector. In summary, our results show that the geminivirus-encoded C2 interacts with JAZ8 in the nucleus, and suggest that this plant protein exerts an anti-geminiviral effect.

Nucieocytoplasmic Shuttling of Geminivirus C4 Protein Mediated by Phosphorylation and Myristoylation Is Critical for Viral Pathogenicity

Many geminivirus C4 proteins induce severe developmental abnormalities in plants.We previously demon- strated that Tomato leaf curl Yunnan virus (TLCYnV)C4 induces plant developmental abnormalities at least partically by decreasing the accumulation of NbSKη,an ortholog of Arabidopsis BIN2 kinase involved in the brassinosteroid signaling pathway,in the nucleus through directing it to the plasma membrane.However, the molecular mechanism by which the membrane-associated C4 modifies the localization of NbSKη in the host cell remains unclear.Here,we show that TLCYnV C4 is a nucleocytoplasmic shuttle protein,and that C4 shuttling is accompanied by nuclear export of NbSKTI.TLCYnV C4 is phosphorylated by NbSKη in the nucleus,which promotes myristoylation of the viral protein.Myristoylation of phosphorylated C4 favors its interaction with exportin-α(XPO I);which in turn facilitates nuclear export of the C4/NbSKTI complex. Supporting this model,chemical inhibition of N-myristoyltransferases or exportin-α enhanced nuclear retention of C4,and mutations of the putative phosphorylation or myristoylation sites in C4 resulted in increased nuclear retention ofrC4 and thus decreased severity of C4-induced developmental abnormalities. The impact of C4 on development is also lessened when a nuclear localization signal or a nuclear export signal is added to its C-terminus,restricting it to a specific cellular niche and therefore impairing nucleocytoplasmic shuttling.Taken together,our results suggest that nucleocytoplasmic shuttling of TLCYnV C4,enabled by phosphorylation by NbSKη,myristoylation,and interaction with exportin-α is critical for its function as a pathogenicity factor.

DET1-mediated COP1 regulation avoids HY5 activity over second-site gene targets to tune plant photomorphogenesis

DE-ETIOLATED 1(DET1)and CONSTITUTIVE PHOTOMORPHOGENESIS 1(COP1)are two essential repressors of Arabidopsis photomorphogenesis.These proteins can associate with CULLIN4 to form independent CRL4-based E3 ubiquitin ligases that mediate the degradation of several photomorphogenic transcription factors,including ELONGATED HYPOCOTYL 5(HY5),thereby controlling multiple gene-regulatory networks.Despite extensive biochemical and genetic analyses of their multi-subunit complexes,the functional links between DET1 and COP1 have long remained elusive.Here,we report that DET1 associates with COP1 in vivo,enhances COP1-HY5 interaction,and promotes COP1 destabilization in a process that dampens HY5 protein abundance.By regulating its accumulation,DET1 avoids HY5 association with hundreds of second-site genomic loci,which are also frequently targeted by the skotomorphogenic transcription factor PHYTOCHROME-INTERACTING FACTOR 3.Accordingly,ectopic HY5 chromatin enrichment favors local gene repression and can trigger fusca-like phenotypes.This study therefore shows that DET1-mediated regulation of COP1 stability tunes down the HY5 cistrome,avoiding hyper-photomorphogenic responses that might compromise plant viability.

RNA-directed DNA methylation has an important developmental function in Arabidopsis that is masked by the chromatin remodeler PICKLE^FA

In Arabidopsis,RNA-directed DNA methylation(RdDM)is required for the maintenance of CHH methylation,and for denovo methylation in all(CG,CHG,and CHH)contexts,but no obvious effect of RdDM deficiency on plant developmenthas been found to date.We show that the combination of mutations in the chromatin remodeler PKL and RdDMcomponents results in developmental alterations,which appear in a SUPPRESSOR OF DRMI DRM2 CMT3(SDC)dependent manner.

A novel protein complex that regulates active DNA demethylation in Arabidopsis

Active DNA demethylation is critical for altering DNA methylation patterns and regulating gene expression.The 5-methylcytosine DNA glycosylase/lyase ROS1 initiates a base-excision repair pathway for active DNA demethylation and is required for the prevention of DNA hypermethylation at 1000 s of genomic regions in Arabidopsis.How ROS1 is regulated and targeted to specific genomic regions is not well understood.Here,we report the discovery of an Arabidopsis protein complex that contains ROS1,regulates ROS1 gene expression,and likely targets the ROS1 protein to specific genomic regions.ROS1 physically interacts with a WD40 domain protein(RWD40),which in turn interacts with a methyl-DNA binding protein(RMB1)as well as with a zinc finger and homeobox domain protein(RHD1).RMB1 binds to DNA that is methylated in any sequence context,and this binding is necessary for its function in vivo.Loss-of-function mutations in RWD40,RMB1,or RHD1 cause DNA hypermethylation at several tested genomic regions independently of the known ROS1 regulator IDM1.Because the hypermethylated genomic regions include the DNA methylation monitoring sequence in the ROS1 promoter,plants mutated in RWD40,RMB1,or RHD1 show increased ROS1 expression.Importantly,ROS1 binding to the ROS1 promoter requires RWD40,RMB1,and RHD1,suggesting that this complex dictates ROS1 targeting to this locus.Our results demonstrate that ROS1 forms a protein complex with RWD40,RMB1,and RHD1,and that this novel complex regulates active DNA demethylation at several endogenous loci in Arabidopsis.

Plant biotic interactions: From fundamental research toward sustainable agriculture

Plants not only provide food and natural materials for humankind, but also constitute an indispensable part of the ecological system of this planet:without plants, life as we know it would simply not be possible. Through their lifespans,plants interact with a plethora of other organisms, including beneficial microbes and potential pathogens. Dissecting the underlying mechanisms determining the outcome of plant biotic interactions is a cornerstone for the design of rational management strategies to secure global food production and ecological balance.

Plant viruses as probes to engineer tolerance to abiotic stress in crops

Main text Plants,as sessile organisms,have to deploy a vast array of mechanisms to cope with the always-changing environmental conditions that surround them.The increasing accumulation of greenhouse gases in the atmosphere in the last century is responsible for a global warming of which the effects are predicted to be magnified in the near future.

Chloroplast immunity: A cornerstone of plant defense

Increasing evidence supports the notion that pattern-recognition-receptor-mediated immunity goes beyond plasma membrane-to-nucleus signaling.With the findings of the pathways linking plasma membrane and chloroplasts and the functions of stromules and perinuclear chloroplast clustering(PCC)in plant defense,chloroplast immunity has emerged as a cornerstone of plant defense and a target of plant pathogens.