Dear Editor,As one of the most widespread and destructive families of plant viruses,Geminiviridae,named for the twinned icosahedral parti-cles of virus members in the family,poses a serious threat to agri-cultural production worldwide.Transmitted by various homop-terans insects such as whiteflies,leafhoppers,aphids,and treehoppers,geminiviruses infect,in addition to wild plants,vegetable,root,and fiber crops,thus causing important losses around the globe(Hanley-Bowdoin et al.,2013;Li et al.,2022).

Jasmonates(JAs)are phytohormones that finely regulate critical biological processes,including plant development and defense.JASMONATE ZIM-DOMAIN(JAZ)proteins are crucial transcrip-tional 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 tran-scription factors and,consequently,the induction of JA-responsive genes.A growing body of evi-dence has shown that JA signaling is crucial in defending against plant viruses and their insect vectors.Here,we describe the interaction of C2 proteins 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 C2 proteins colocalize in the nucleus,forming dis-crete nuclear speckles.Overexpression of JAZ8 did not lead to altered responses to TYLCV in-fection 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 ob-vious developmental phenotypes nor present dif-ferences 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.

Geminiviruses are a family of plant viruses that cause devastating diseases in many economically important crops worldwide.These pathogens encapsidate circular,single-stranded DNAs (ssDNAs) of 2.5-3.0 kb that replicate through double-stranded DNA (dsDNA) intermediates.Members of the genus Begomovirus,which comprises by far the largest number of species in the family,are transmitted by whiteflies and have genomes consisting of one or two DNAs.Most monopartite begomoviruses associate with betasatellites,which have circular ssDNA genomes that are half the size (～1.3 kb) of their helper viruses.Betasatellites encode a single protein (βC1)that reprograms cellular processes to facilitate infection and is both a target and a repressor of host defenses.During the long-term arms race between plants and geminiviruses,plants have evolved multiple defense mechanisms to safeguard against infection.Here,we discuss several recent reports that provide new insight into plant defenses against geminivirus-betasatellite complexes and viral counter-defense measures.

Many geminivirus C4 proteins induce severe developmental abnormalities in plants.We previously demonstrated that Tomato leafcurlYunnan 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 NbSKη.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-β (XPO I),which in turn facilitates nuclear export of the C4/NbSKη 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 of C4 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.

Geminiviruses (family Geminiviridae) are among the most devastating plant pathogens worldwide,causing heavy losses on food and cash crops and representing a threat to global food security and sustainability.These viruses have very compact genomes comprising one (monopartite) or two (bipartite) circular singlestranded DNA (ssDNA) molecules,each ranging from 2.6 to 2.8 kb.Amplification of geminiviral genome is achieved through a combination of rolling circle and recombination-mediated replication,producing double-stranded (ds) DNA replication form intermediates.Because of the very compact nature of geminiviral genomes,viral proteins have multiple functions.The smallest geminivirus open reading frame (ORF) codes for C4 in monopartite viruses or AC4 in bipartite viruses and is embedded within the coding region of the replication initiation protein (Rep),which is in a different ORF.C4 has long been demonstrated to be required for monopartite geminivirus infection.More recently,AC4 of African cassava mosaic virus (ACMV) (Hipp et al.,2016) and of Mungbean yellow mosaic virus (MYMV) (Carluccio et al.,2018) were shown to be required for virus infection.

DEAR EDITOR,Plant viruses make up almost half of the plant disease-causing pathogens,affecting crop yields and the global economy(Savary et al.,2019).Soybean(Glycine max)is one of the most valuable legume crops in the world,supplying 25％of the global edible oil and two-thirds of the global concentrated protein for livestock feeding.Recently,the outbreak of soybean stay-green syndrome with delayed leaf senescence(stay-green),flat pods,and increased number of abnormal seeds has swept the soybean production in the Huang-Huai-Hai region of China,resulting in huge yield losses(Xu et al.,2019).This disease has become an epidemic and prominent problem in soybean production and is still expanding its geography,including North America,posing a serious threat to soybean production(Harbach et al.,2016;Zhang et al.,2016;Li et al.,2019).However,the cause of soybean stay-green syndrome remains obscure.

With the widespread use of clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas) tech-nologies in plants, large-scale genome editing is increasingly needed. Here, we developed a geminivirus-mediated surrogate system, called Wheat Dwarf Virus-Gate (WDV-surrogate), to facilitate high-throughput genome editing. WDV-Gate has two parts: one is the recipient callus from a transgenic rice line expressing Cas9 and a mutated hygromycin-resistant gene (HygM) for surrogate selection; the other is a WDV-based construct expressing two single guide RNAs (sgRNAs) targeting HygM and a gene of interest, respectively. We evaluated WDV-Gate on six rice loci by producing a total of 874 T0 plants. Compared with the conventional method, the WDV-Gate system, which was characterized by a transient and high level of sgRNA expression, significantly increased editing frequency (66.8％ vs. 90.1％), plantlet regeneration efficiency (2.31-fold increase), and numbers of homozygous-edited plants (36.3％vs. 70.7％). Large-scale editing using pooled sgRNAs targeting the SLR1 gene resulted in a high editing frequency of 94.4％, further dem-onstrating its feasibility. We also tested WDV-Gate on sequence knock-in for protein tagging. By co-delivering a chemically modified donor DNA with the WDV-Gate plasmid, 3xFLAG pep-tides were successfully fused to three loci with an efficiency of up to 13％. Thus, by combining transiently expressed sgRNAs and a surrogate selection system, WDV-Gate could be useful for high-throughput gene knock-out and sequence knock-in.

Autophagy is a conserved intracellular degrada-tion process that plays an active role in plant re-sponse to virus infections.Here we report that geminiviruses counteract activated autophagy-mediated antiviral defense in plant cells through the C2 proteins they encode.We found that,in Nicotiana benthamiana plants,tomato leaf curl Yunnan virus(TLCYnV)infection upregulated the transcription levels of autophagy-related genes(ATGs).Overexpression of NbATG5,NbATG7,or NbATG8a in N.benthamiana plants decreased TLCYnV accumulation and attenuated viral symp-toms.Interestingly,transgenic overexpression of NbATG7 promoted the growth of N.benthamiana plants and enhanced plant resistance to TLCYnV.We further revealed that the C2 protein encoded by TLCYnV directly interacted with the ubiquitin-activating domain of ATG7.This interaction com-petitively disrupted the ATG7–ATG8 binding in N.benthamiana and Solanum lycopersicum plants,thereby inhibiting autophagy activity.Fur-thermore,we uncovered that the C2-mediated autophagy inhibition mechanism was conserved in three other geminiviruses.In summary,we dis-covered a novel counter-defensive strategy em-ployed by geminiviruses that enlists their C2 pro-teins as disrupters of ATG7–ATG8 interactions to defeat antiviral autophagy.