Gene VI Research Articles

Disruption of the Chitin Biosynthetic Pathway Results in Significant Changes in the Cell Growth Phenotypes and Biosynthesis of Secondary Metabolites of Monascus purpureus.

In this study, the gene monascus-5162 from Monascus purpureus LQ-6, identified as chitin synthase gene VI (chs6), was knocked out to disrupt the chitin biosynthetic pathway and regulate the biosynthesis of Monascus pigments (MPs) and citrinin. The results showed that the aerial hyphae on a solid medium were short and sparse after the deletion of chs6 in M. purpureus LQ-6, significantly reducing the germination percentage of active spores to approximately 22%, but the colony diameter was almost unaffected. Additionally, the deletion of chs6 changed the mycelial morphology of M. purpureus LQ-6 during submerged fermentation and increased its sensitivity to environmental factors. MP and citrinin biosynthesis was dramatically inhibited in the recombinant strain. Furthermore, comparative transcriptome analysis revealed that the pathways related to spore development and growth, including the MAPK signaling pathway, chitin biosynthetic pathway, and regulatory factors LaeA and WetA genes, were significantly downregulated in the early phase of fermentation. The mRNA expression levels of genes in the cluster of secondary metabolites were significantly downregulated, especially those related to citrinin biosynthesis. This is the first detailed study to reveal that chs6 plays a vital role in regulating the cell growth and secondary metabolism of the Monascus genus.

CDNA phage display for the discovery of theranostic autoantibodies in rheumatoid arthritis.

Rheumatoid arthritis (RA) is the world's most common autoimmune disease mainly characterized by a chronic inflammation of multiple synovial joints. Rheumatologists now have a whole range of treatment options including glucocorticoids (GCs), classical synthetic and biological disease-modifying antirheumatic drugs (cs- and bDMARDS), resulting in a tremendous improvement in treatment outcomes for RA patients over the last two decades. Despite this progress, the choice of treatment regimen to achieve stable remission at the individual patient level still largely depends on trial and error. In this review, the need for novel theranostic markers that can predict a patient's response to methotrexate, the standard first-line csDMARD treatment, is discussed. Like in many autoimmune diseases, the majority of RA patients form a whole range of autoantibodies. We aim to find novel theranostic autoantibody markers using serological antigen selection, a high-throughput technique that uses cDNA phage display to identify novel antigen targets. We have constructed a barcoded cDNA phage display library from the synovial tissue of three RA patients by fusing cDNA products to the filamentous phage minor coat protein VI. This library contains a large proportion of full-length genes and gene fragments that are cloned in frame with the phage gene VI. By screening this library for antibody reactivity in serum samples of patients from the CareRA trial, which compared different intensive treatment strategies based on csDMARDs and a step-down GC schedule, our cDNA phage display library has great potential for the discovery of novel theranostic autoantibody biomarkers.

Mutations within A 35 amino acid region of P6 influence self-association, inclusion body formation, and Caulimovirus infectivity

Cauliflower mosaic virus gene VI product (P6) is an essential protein that forms cytoplasmic, inclusion bodies (IBs). P6 contains four regions involved in self-association, termed D1–D4. D3 binds to D1, along with D4 and contains a spacer region (termed D3b) between two RNA-binding domains. Here we show D3b binds full-length P6 along with D1 and D4. Full-length P6s harboring single amino acid substitutions within D3b showed reduced binding to both D1 and D4. Full-length P6s containing D3b mutations and fused with green fluorescent protein formed inclusion-like bodies (IL-Bs) when expressed in Nicotiana benthamiana leaves. However, mutant P6s with reduced binding to D1 and D4, showed smaller IL-Bs, than wild type. Likewise, viruses containing these mutations showed a decrease in inoculated leaf viral DNA levels and reduced efficiency of systemic infection. These data suggest that mutations influencing P6 self-association alter IB formation and reduce virus infection.

The P6 protein of Cauliflower mosaic virus interacts with CHUP1, a plant protein which moves chloroplasts on actin microfilaments

The gene VI product, protein 6 (P6), of Cauliflower mosaic virus (CaMV) assembles into large, amorphous inclusion bodies (IBs) that are considered sites for viral protein synthesis and viral genome replication and encapsidation. P6 IBs align with microfilaments and require them for intracellular trafficking, a result implying that P6 IBs function to move virus complexes or virions within the cell to support virus physiology. Through a yeast two-hybrid screen we determined that CHUP1, a plant protein allowing chloroplast transport through an interaction with chloroplast and microfilament, interacts with P6. The interaction between CHUP1 and P6 was confirmed through colocalization in vivo and co-immunoprecipitation assays. A truncated CHUP1 fused with enhanced cyan fluorescent protein, unable to transport chloroplasts, inhibited intracellular movement of P6–Venus inclusions. Silencing of CHUP1 in N. edwardsonii impaired the ability of CaMV to infect plants. The findings suggest that CHUP1 supports CaMV infection through an interaction with P6.

Possible consequences of the overlap between the CaMV 35S promoter regions in plant transformation vectors used and the viral gene VI in transgenic plants

Multiple variants of the Cauliflower mosaic virus 35S promoter (P35S) are used to drive the expression of transgenes in genetically modified plants, for both research purposes and commercial applications. The genetic organization of the densely packed genome of this virus results in sequence overlap between P35S and viral gene VI, encoding the multifunctional P6 protein. The present paper investigates whether introduction of P35S variants by genetic transformation is likely to result in the expression of functional domains of the P6 protein and in potential impacts in transgenic plants. A bioinformatic analysis was performed to assess the safety for human and animal health of putative translation products of gene VI overlapping P35S. No relevant similarity was identified between the putative peptides and known allergens and toxins, using different databases. From a literature study it became clear that long variants of the P35S do contain an open reading frame, when expressed, might result in unintended phenotypic changes. A flowchart is proposed to evaluate possible unintended effects in plant transformants, based on the DNA sequence actually introduced and on the plant phenotype, taking into account the known effects of ectopically expressed P6 domains in model plants.

Cauliflower mosaic virus major inclusion body protein interacts with the aphid transmission factor, the virion-associated protein, and gene VII product

The Cauliflower mosaic virus (CaMV) gene VI product (P6) is a multifunctional protein essential for viral infection. In order to perform its various tasks, P6 interacts with both viral and host factors, as well as forming electron-dense cytoplasmic inclusion bodies. Here we investigate the interactions of P6 with three CaMV proteins: P2 (aphid transmission factor), P3 (virion-associated protein), and P7 (protein of unknown function). Based on yeast two-hybrid and maltose-binding protein pull-down experiments, P6 interacted with all three of these CaMV proteins. P2 helps to stabilize P6 inclusion bodies. Although the P2s from two CaMV isolates (W260 and CM1841) differ in the ability to stabilize inclusion bodies, both interacted similarly with P6. This suggests that inclusion body stability may not be dependent on the efficiency of P2–P6 interaction. However, neither P2 nor P3 interacted with P7 in yeast two-hybrid assays.

The Dahlia mosaic virus gene VI product N-terminal region is involved in self-association

The genome of the floriculture pathogen Dahlia mosaic caulimovirus (DMV) encodes six open reading frames. Generally, caulimovirus gene VI products (P6s) are thought to be multifunctional proteins required for viral infection and it is likely that self-association is required for some of these functions. In this study, yeast two-hybrid and maltose binding protein (MBP) pull-down assays indicated that full-length DMV P6 specifically self-associates. Further analyses indicated that only the DMV P6 N-terminal region, consisting of 115 amino acids, interacts with full-length P6 and with itself. This distinguishes the DMV P6 from its Cauliflower mosaic virus counterpart, which contains four regions involved in self-association. Thus, our results suggest that each caulimovirus P6 may possess a unique pattern of protein–protein interactions. Bioinformatic tools identified a putative nuclear exclusion signal located between amino acid residues 10–20, suggesting another possible function for the P6 N-terminal region.

The Cauliflower Mosaic Virus Protein P6 Forms Motile Inclusions That Traffic along Actin Microfilaments and Stabilize Microtubules

The gene VI product (P6) of Cauliflower mosaic virus (CaMV) is a multifunctional protein known to be a major component of cytoplasmic inclusion bodies formed during CaMV infection. Although these inclusions are known to contain virions and are thought to be sites of translation from the CaMV 35S polycistronic RNA intermediate, the precise role of these bodies in the CaMV infection cycle remains unclear. Here, we examine the functionality and intracellular location of a fusion between P6 and GFP (P6-GFP). We initially show that the ability of P6-GFP to transactivate translation is comparable to unmodified P6. Consequently, our work has direct application for the large body of literature in which P6 has been expressed ectopically and its functions characterized. We subsequently found that P6-GFP forms highly motile cytoplasmic inclusion bodies and revealed through fluorescence colocalization studies that these P6-GFP bodies associate with the actin/endoplasmic reticulum network as well as microtubules. We demonstrate that while P6-GFP inclusions traffic along microfilaments, those associated with microtubules appear stationary. Additionally, inhibitor studies reveal that the intracellular movement of P6-GFP inclusions is sensitive to the actin inhibitor, latrunculin B, which also inhibits the formation of local lesions by CaMV in Nicotiana edwardsonii leaves. The motility of P6 along microfilaments represents an entirely new property for this protein, and these results imply a role for P6 in intracellular and cell-to-cell movement of CaMV.

Cauliflower mosaic virus gene VI product N-terminus contains regions involved in resistance-breakage, self-association and interactions with movement protein

Cauliflower mosaic virus (CaMV) gene VI encodes a multifunctional protein (P6) involved in the translation of viral RNA, the formation of inclusion bodies, and the determination of host range. Arabidopsis thaliana ecotype Tsu-0 prevents the systemic spread of most CaMV isolates, including CM1841. However, CaMV isolate W260 overcomes this resistance. In this paper, the N-terminal 110 amino acids of P6 (termed D1) were identified as the resistance-breaking region. D1 also bound full-length P6. Furthermore, binding of W260 D1 to P6 induced higher β-galactosidase activity and better leucine-independent growth in the yeast two-hybrid system than its CM1841 counterpart. Thus, W260 may evade Tsu-0 resistance by mediating P6 self-association in a manner different from that of CM1841. Because Tsu-0 resistance prevents virus movement, interaction of P6 with P1 (CaMV movement protein) was investigated. Both yeast two-hybrid analyses and maltose-binding protein pull-down experiments show that P6 interacts with P1. Although neither half of P1 interacts with P6, the N-terminus of P6 binds P1. Interestingly, D1 by itself does not interact with P1, indicating that different portions of the P6 N-terminus are involved in different activities. The P1–P6 interactions suggest a role for P6 in virus transport, possibly by regulating P1 tubule formation or the assembly of movement complexes.

Protist Homologs of the Meiotic Spo11 Gene and Topoisomerase VI reveal an Evolutionary History of Gene Duplication and Lineage-Specific Loss

Spo11 is a meiotic protein of fundamental importance as it is a conserved meiosis-specific transesterase required for meiotic recombination initiation in fungi, animals, and plants. Spo11 is homologous to the archaebacterial topoisomerase VIA (Top6A) gene, and its homologs are broadly distributed among eukaryotes, with some eukaryotes having more than one homolog. However, the evolutionary relationships among these genes are unclear, with some debate as to whether eukaryotic homologs originated by lateral gene transfer. We have identified and characterized protist Spo11 homologs by degenerate polymerase chain reaction (PCR) and sequencing and by analyses of sequences from public databases. Our phylogenetic analyses show that Spo11 homologs evolved by two ancient eukaryotic gene duplication events prior to the last common ancestor of extant eukaryotes, resulting in three eukaryotic paralogs: Spo11-1, Spo11-2, and Spo11-3. Spo11-1 orthologs encode meiosis-specific proteins and are distributed broadly among eukaryotic lineages, though Spo11-1 is absent from some protists. This absence coincides with the presence of Spo11-2 orthologs, which are meiosis-specific in Arabidopsis and are found in plants, red algae, and some protists but absent in animals and fungi. Spo11-3 encodes a Top6A subunit that interacts with topoisomerase VIB (Top6B) subunits, which together play a role in vegetative growth in Arabidopsis. We identified Spo11-3 (Top6A) and Top6B homologs in plants, red algae, and a few protists, establishing a broader distribution of these genes among eukaryotes, indicating their likely vertical descent followed by lineage-specific loss.

Arabidopsis mutants that suppress the phenotype induced by transgene-mediated expression of cauliflower mosaic virus (CaMV) gene VI are less susceptible to CaMV-infection and show reduced ethylene sensitivity

Protein P6 is the main symptom determinant of cauliflower mosaic virus (CaMV), and transgene-mediated expression in Arabidopsis induces a symptom-like phenotype in the absence of infection. Seeds of a P6-transgenic line, A7, were mutagenized by gamma-irradiation and M2 seedlings were screened for mutants that suppressed the phenotype of chlorosis and stunting. We identified four mutants that were larger and less chlorotic than the A7 parent but which contained an intact and transcriptionally active transgene. The two mutants with the strongest suppression phenotype, were recessive and allelic. The transgene was eliminated by back-crossing with wild-type Arabidopsis. In progeny lines that were homozygous for the putative suppressor mutation the proportion of plants becoming infected following inoculation with CaMV was 40% that of wild-type, although in plants that did become infected, levels of virus DNA in mutants and wild-type did not differ significantly. Symptoms in the mutants were milder and delayed although this was somewhat dependent on the virus isolate. This phenotype was inherited stably. Both mutant alleles showed a partially ethylene-insensitive phenotype in an ethylene triple response assay. P6-transgenic plants were also almost completely insensitive to ethylene in the triple response assay. We suggest that the chlorosis and stunting in P6-transgenic and CaMV-infected plants are dependent on interactions between P6 and components involved in ethylene signalling, and that the suppressor gene product may function to augment these interactions.

Differential induction of symptoms in Arabidopsis by P6 of Cauliflower mosaic virus.

The gene VI protein (P6) of Cauliflower mosaic virus (CaMV) functions as a virulence factor in crucifers by eliciting chlorotic symptoms in infected plants. The ability to induce chlorosis has been associated previously with P6 through gene-swapping experiments between strains and through the development of transgenic plants that express P6. The primary role that has been identified for P6 in the CaMV infection cycle is to modify the host translation machinery to facilitate the translation of the polycistronic CaMV 35S RNA. This function for P6 has been designated as the translational transactivator (TAV) function. In the present study, we have characterized an unusual variant of P6, derived from CaMV strain D4, that does not induce chlorosis upon transformation into Arabidopsis thaliana. The level of D4 P6 produced in transgenic Arabidopsis line D4-2 was comparable to the amount found in transgenic plants homozygous for W260 and CM1841 P6, two versions of P6 that induce strong chlorotic symptoms and stunting in Arabidopsis. A complementation assay proved that P6 expressed in the D4-2 line was functional, as it could support the systemic infection of a CM1841 mutant that contained a lethal frame-shift mutation within gene VI. This complementation assay allowed us to separately assess the contribution of CM1841 gene VI to symptom development versus the contribution of other CM1841 genes. Furthermore, a previous study had shown that the TAV activity of D4 P6 was comparable to that of W260 P6. That comparative analysis of TAV function, coupled with the characterization of the D4-2 transgenic line in the present paper, indicates that the TAV function of P6 may play only a minor role in the development of chlorotic symptoms.

Multiple domains within the Cauliflower mosaic virus gene VI product interact with the full-length protein.

The Cauliflower mosaic virus (CaMV) gene VI product (P6) is a multifunctional protein essential for viral propagation. It is likely that at least some of these functions require P6 self-association. The work described here was performed to confirm that P6 self-associates and to identify domains involved in this interaction. Yeast two-hybrid analyses indicated that full-length P6 self-associates and that this interaction is specific. Additional analyses indicated that at least four independent domains bind to full-length P6. When a central domain (termed domain D3) was removed, these interactions were abolished. However, this deleted P6 was able to bind to the full-length wild-type protein and to isolated domain D3. Viruses lacking domain D3 were incapable of producing a systemic infection. Isolated domain D3 was capable of binding to at least two of the other domains but was unable to self-associate. This suggests that domain D3 facilitates P6 self-association by binding to the other domains but not itself. The presence of multiple domains involved in P6 self-association may help explain the ability of this protein to form the intracellular inclusions characteristic of caulimoviruses.

A Comparative Analysis of the Avirulence and Translational Transactivator Functions of Gene VI of Cauliflower mosaic virus

The primary function associated at present with the gene VI product of Cauliflower mosaic virus (CaMV) is that of a translational transactivator (TAV). In this capacity, it alters the host translational machinery to allow reinitiation of translation of other CaMV genes on the polycistronic 35S RNA of CaMV. In addition, the gene VI protein can elicit a specific type of plant defense response called the hypersensitive response (HR) in Nicotiana edwardsonii. In this study, we have adapted the agroinfiltration technique to compare the sequences of CaMV gene VI required for TAV function and elicitation of HR. To measure the activity of the TAV, we coagroinfiltrated gene VI of CaMV strain W260 with a bicistronic GUS reporter plasmid. TAV function could be assayed 4 days postinfiltration, before the onset of HR in N. edwardsonii. Through the use of the TAV and HR assays, we could show that the TAV functions of gene VI of CaMV strains W260 and D4 were equivalent, but only W260 gene VI elicited HR. A mutational analysis of W260 gene VI showed that the structural requirements for elicitation of HR were much more stringent than those for TAV function. Small deletions from either the 5′ or 3′ end of W260 gene VI abolished its ability to elicit HR, although the TAV function was retained in the mutant. The TAV function could also tolerate a small insertion within gene VI; this insertion abolished the elicitor function. This study provides direct evidence that the TAV function of gene VI is separate from its role as an elicitor of HR.

The 5′ Third of Cauliflower mosaic virus Gene VI Conditions Resistance Breakage in Arabidopsis Ecotype Tsu-0

ABSTRACT Arabidopsis thaliana ecotypes vary in their responses to viruses. In this study, we analyzed the variation in response of A. thaliana ecotype Tsu-0 to Cauliflower mosaic virus (CaMV). This ecotype was previously reported to be resistant to two CaMV isolates (CM1841 and CM4-184), but susceptible to W260. In this study, we show that Tsu-0 is resistant to four additional CaMV isolates. CaMV propagated within the rosette leaves of Tsu-0 plants, but did not appear to spread systemically into the inflorescence. However, virus viability in rosette leaves of Tsu-0 plants apparently was not compromised because infectious CaMV could be recovered from these organs. W260 overcomes Tsu-0 resistance by a passive mechanism (i.e., this virus avoids activating plant defenses). The portion of the viral genome responsible for W260 resistance breakage was mapped to the 5' third of gene VI, which we have termed RBR-1. This region is also responsible for controlling the ability of CaMV to infect different types of solanaceous plants. Hence, the pathways by which plants of different families interact with CaMV may be conserved through evolution.

Precursor T-cell acute lymphoblastic leukemia in adults: age-related immunophenotypic, cytogenetic, and molecular subsets.

We analyzed the clinicopathologic and molecular findings in 26 adults (age 16-72 years) with T-cell acute lymphoblastic leukemia (T-ALL) and observed features that correlated with age. Patients older than 60 years (n = 5) had a low frequency of hepatosplenomegaly (0 [0%]), anterior mediastinal mass (1 [20%]), and lymphadenopathy (2 [40%]), and completely responded to chemotherapy (4 of 4). The T-ALL in this group commonly expressed myeloid antigens (4 [80%]), had lineage-inappropriate gene rearrangements (2/3 [67%]) and chromosome 2 deletion (3/4 [75%]), and exclusively used the V(III) or V(IV) families of the T-cell receptor (TCR) gamma gene. In comparison, patients 16 to 60 years old (n = 21) more commonly had an anterior mediastinal mass (8 [38%]), hepatosplenomegaly (10 [48%]), and lymphadenopathy (16 [76%]). The tumors in these patients commonly used the TCR gamma gene VI or V(II) families (17/25 total rearrangements [68%]). Myeloid antigen expression (5 [24%]) and lineage inappropriate gene rearrangements (4/15 [27%]) were uncommon. Within this group, CD1a expression correlated with age 28 to 60 years. These results illustrate considerable age-related heterogeneity in adult T-ALL, which may reflect differences in tumor cell maturation.

Agroinfiltration of Cauliflower mosaic virus gene VI elicits hypersensitive response in Nicotiana species.

Cauliflower mosaic virus strain W260 induces hypersensitive response (HR) in Nicotiana edwardsonii and systemic cell death in N. clevelandii. In contrast, the D4 strain of Cauliflower mosaic virus evades the host defenses in Nicotiana species; it induces chlorotic primary lesions and a systemic mosaic in both hosts. Previous studies with chimeric viruses had indicated that gene VI of W260 was responsible for elicitation of HR or cell death. To prove conclusively that W260 gene VI is responsible, we inserted gene VI of W260 and D4 into the Agrobacterium tumefaciens binary vector pKYLX7. Agroinfiltration of these constructs into the leaves of N. edwardsonii and N. clevelandii revealed that gene VI of W260 elicited HR in N. edwardsonii 4 to 5 days after infiltration and cell death in N. clevelandii approximately 9 to 12 days after infiltration. In contrast, gene VI of D4 did not elicit HR or cell death in either Nicotiana species. A frameshift mutation introduced into gene VI of W260 abolished its ability to elicit HR or cell death in both Nicotiana species, demonstrating that the elicitor is the gene VI protein.

Cauliflower mosaic virus infection stimulates lipid transfer protein gene expression in Arabidopsis

Lipid transfer proteins (LTPs), are encoded in plants by multi-gene families, and have been implicated in the defence response to bacterial and fungal infection. Levels of LTP transcripts in Arabidopsis systemically infected with either a mild or a severe isolate of CaMV, were elevated approximately 3-5-fold compared to uninfected controls. In CaMV-infected transgenic Arabidopsis containing a GUS reporter gene under the control of an LTP promoter from Brassica napus, high levels of GUS in the leaves, root hairs and lateral root were observed, whereas mock inoculated controls showed markedly lower expression. A second construct, with one of the Arabidopsis LTP promoters, did not show increased GUS expression following infection. CaMV gene VI is a major determinant of symptom phenotype and constitutive transgene-mediated expression induces a symptom-like phenotype. Levels of LTP mRNA were elevated in transgenic plants expressing high levels of gene VI protein, and double transgenics that contained the BnLTP::GUS transgene and expressed high levels of gene VI protein, stained intensely for GUS activity. These observations suggest that the response to systemic infection by CaMV includes transcription of some, but probably not all of the LTP genes. Expression of CaMV gene VI appears to be important in triggering this process.

Cauliflower mosaic virus infection stimulates lipid transfer protein gene expression in Arabidopsis

Lipid transfer proteins (LTPs), are encoded in plants by multi-gene families, and have been implicated in the defence response to bacterial and fungal infection. Levels of LTP transcripts in Arabidopsis systemically infected with either a mild or a severe isolate of CaMV, were elevated approximately 3-5-fold compared to uninfected controls. In CaMV-infected transgenic Arabidopsis containing a GUS reporter gene under the control of an LTP promoter from Brassica napus, high levels of GUS in the leaves, root hairs and lateral root were observed, whereas mock inoculated controls showed markedly lower expression. A second construct, with one of the Arabidopsis LTP promoters, did not show increased GUS expression following infection. CaMV gene VI is a major determinant of symptom phenotype and constitutive transgene-mediated expression induces a symptom-like phenotype. Levels of LTP mRNA were elevated in transgenic plants expressing high levels of gene VI protein, and double transgenics that contained the BnLTP::GUS transgene and expressed high levels of gene VI protein, stained intensely for GUS activity. These observations suggest that the response to systemic infection by CaMV includes transcription of some, but probably not all of the LTP genes. Expression of CaMV gene VI appears to be important in triggering this process.

Systemic Cell Death Is Elicited by the Interaction of a Single Gene in Nicotiana clevelandii and Gene VI of Cauliflower Mosaic Virus

Cauliflower mosaic virus (CaMV) strains D4 and W260 can be distinguished by the type of symptoms they induce in Nicotiana clevelandii and N. edwardsonii. W260 induces systemic cell death in addition to a mosaic symptom in N. clevelandii and a hypersensitive response (HR) in N. edwardsonii, whereas D4 induces a systemic mosaic in both hosts. To determine which W260 genes are responsible for systemic cell death, chimeric viruses were constructed between the D4 and W260 strains. It was found that W260 gene VI was responsible for the elicitation of systemic cell death; previous studies had shown that this same gene elicited HR in N. edwardsonii. An immunological analysis of plants infected with W260 or D4 indicated that the systemic cell death symptom was not associated with enhanced levels of either W260 virions or the W260 gene VI product. To investigate the inheritance of systemic cell death, crosses were made between N. clevelandii and N. bigelovii, a host that reacts with a systemic mosaic symptom upon infection with W260. All F1 plants developed a systemic mosaic after inoculation with W260, whereas the F2 generation segregated 3:1 for systemic mosaic versus cell death. The plant gene responsible for cell death was designated ccd1, for CaMV cell death gene. These results demonstrate that the systemic cell death symptom in N. clevelandii is induced by the interaction between a single host gene and gene VI of CaMV.