A Genome-Wide Comparison of Rice False Smut Fungus Villosiclava virens Albino Strain LN02 Reveals the Genetic Diversity of Secondary Metabolites and the Cause of Albinism.

Rice false smut (RFS) caused by Villosiclava virens (anamorph: Ustilaginoidea virens) has become one of the most destructive fungal diseases to decrease the yield and quality of rice grains. An albino strain LN02 was isolated from the white RFS balls collected in the Liaoning Province of China in 2019. The strain LN02 was considered as a natural albino mutant of V. virens by analyzing its phenotypes, internal transcribed spacer (ITS) conserved sequence, and biosynthesis gene clusters (BGCs) for secondary metabolites. The total assembled genome of strain LN02 was 38.81 Mb, which was comprised of seven nuclear chromosomes and one mitochondrial genome with an N50 value of 6,326,845 bp and 9339 protein-encoding genes. In addition, the genome of strain LN02 encoded 19 gene clusters for biosynthesis of secondary metabolites mainly including polyketides, terpenoids and non-ribosomal peptides (NRPs). Four sorbicillinoid metabolites were isolated from the cultures of strain LN02. It was found that the polyketide synthase (PKS)-encoding gene uspks1 for ustilaginoidin biosynthesis in strain LN02 was inactivated due to the deletion of four bases in the promoter sequence of uvpks1. The normal uvpks1 complementary mutant of strain LN02 could restore the ability to synthesize ustilaginoidins. It demonstrated that deficiency of ustilaginoidin biosynthesis is the cause of albinism for RFS albino strain LN02, and V. virens should be a non-melanin-producing fungus. This study further confirmed strain LN02 as a white phenotype mutant of V. virens. The albino strain LN02 will have a great potential in the development and application of secondary metabolites. The physiological and ecological functions of ustilaginoidins in RFS fungus are needed for further investigation.

CSTF2T facilitates pancreatic adenocarcinoma growth and metastasis by elevating H3K4Me1 methylation of CALB2 via ASH2L.

Pancreatic adenocarcinoma (PAAD) is a major cause of mortality related to cancer worldwide. This paper dissected the functions of the CSTF2T/ASH2L/CALB2 axis in PAAD progression. CALB2 expression was assessed in PAAD tissues and cells using RT-qPCR and western blot. Subsequent to gain- and loss-of-function experiments in PAAD cells, cell apoptosis, invasion, proliferation, and migration were examined using flow cytometry, Transwell, CCK-8, and Scratch assays. Additionally, the expression of proliferation markers and apoptotic and metastasis- and invasion-related proteins was measured using western blot. The relationship among CALB2, KMT2D, ASH2L, H3K4Me1, and CSTF2T was evaluated using ChIP, RNA pull-down, RIP, and Co-IP assays. A nude mouse transplantation tumor model was established, with observation of tumor growth and metastasis. CALB2 expression was high in PAAD tissues and cells. Mechanistically, KMT2D was enriched in the CALB2 promoter, and CSTF2T bound to and upregulated ASH2L as a RNA binding protein, which was a core component of the KMT2D complex to enhance CALB2 expression through H3K4Me1 upregulation. CALB2 knockdown diminished the viability, invasion, and migration but elevated the apoptosis of PAAD cells. Likewise, CSTF2T knockdown suppressed the growth and metastasis of PAAD cells and transplanted tumors in nude mice, which was counteracted by further CALB2 overexpression. CSTF2T knockdown blocked the ASH2L/CALB2 axis to protect against PAAD growth and metastasis.

Low SP1 SUMOylation-dependent SNHG17 upregulation promotes drug resistance of gastric cancer through impairing hsa-miR-23b-3p-induced Notch2 inhibition.

OBJECTIVE: Specificity protein 1 (SP1), a transcription factor mediated by SUMOylation modifiers, is upregulated in gastric cancer (GC) and shares negative correlation with patient prognosis. Here, we paid main attention to the role of SP1 SUMOylation in the drug resistance of GC cells and the possible long non-coding RNA (lncRNA) SNHG17/microRNA-23b-3p (miR-23b-3p)/Notch2 network engaged in this process. METHODS: Tumor tissues and non-tumor tissues were isolated from GC patients who received treatment with capecitabine and cisplatin (DDP). Co-immunoprecipitation was utilized to detect the SUMOylation level of SP1. Using gain- and loss-of-function approaches, we assessed the impacts of SNHG17/miR-23b-3p/Notch2 on sensitivity of DDP-resistant GC cells in vitro and in vivo. A series of assays such as luciferase activity detection and RNA pull-down were conducted for mechanistic exploration. RESULTS: SP1 expression was increased due to low SP1 SUMOylation level in the recurrent GC tissues. This increase led to upregulated SNHG17 expression and SP1 binding sites existed in the SNHG17 promoter. In addition, SNHG17 could bind to miR-23b-3p while miR-23b-3p targeted Notch2. Loss of SNHG17 reduced the resistance of DDP-resistant GC cells to DDP, which was achieved through miR-23b-3p-dependent Notch2 inhibition. Finally, SP1 silencing attenuated the resistance of GC to DDP in mice. CONCLUSION: Low SP1 SUMOylation induces SNHG17 upregulation and blocks miR-23b-3p-induced Notch2 inhibition, contributing to the resistance of GC to DDP. This study may aid in the development of therapeutic targets overcoming the chemoresistance of GC.

Ustilaginoidea virens: Insights into an Emerging Rice Pathogen.

False smut of rice, caused by Ustilaginoidea virens, has become one of the most important diseases in rice-growing regions worldwide. The disease causes a significant yield loss and imposes health threats to humans and animals by producing mycotoxins. In this review, we update our understanding of the pathogen, including the disease cycle and infection strategies, the decoding of the U. virens genome, comparative/functional genomics, and effector biology. Whereas the decoding of the U. virens genome unveils specific adaptations of the pathogen in successfully occupying rice flowers, progresses in comparative/functional genomics and effector biology have begun to uncover the molecular mechanisms underlying U. virens virulence and pathogenicity. We highlight the identification and characterization of the produced mycotoxins and their biosynthetic pathways in U. virens.The management strategies for this disease are also discussed. The flower-specific infection strategy makes the pathogen a unique tool to unveil novel mechanisms for the interactions between nonobligate biotrophic pathogens and their hosts.

The false smut pathogen Ustilaginoidea virens requires rice stamens for false smut ball formation.

Rice false smut has emerged as a serious grain disease in rice production worldwide. The disease is characterized by the transformation of individual rice florets into false smut balls, which is caused by the fungal pathogen Ustilaginoidea virens. To date, little is known about the host factors required for false smut ball formation by U. virens. In this study, we identified histological determinants for the formation of false smut balls by inoculating U. virens into rice floral mutants defective with respect to individual floral parts. The results showed that U. virens could form mature false smut balls in rice floral mutants with defective pistils, but failed to develop false smut balls in the superwoman mutant lacking stamens, identifying that U. virens requires rice stamens to complete its infection cycle. Comparative transcriptome analysis indicated a list of candidate host genes that may facilitate nutrient acquisition by U. virens from the rice stamens, such as SWEET11, SWEET14 and SUT5, and genes involved in the biosynthesis of trehalose and raffinose family sugars. These data pinpoint rice stamens as the key target organ of U. virens infection and provide a valuable starting point for dissecting the molecular mechanism of false smut ball formation.

Use of nested PCR for the detection of trichomonads in bronchoalveolar lavage fluid.

BACKGROUND: The methods routinely used to detect trichomonads in the lungs are not sensitive enough, and an effective method is urgently needed. METHOD: Primers were first designed to match the conserved area of the 18S rRNA gene of trichomonads. Then, nested PCR was carried out to detect trichomonads in bronchoalveolar lavage fluid (BALF). Finally, all positive specimens were subjected to DNA sequencing and phylogenetic analysis. RESULTS: Among 115 bronchoalveolar lavage fluid samples, ten samples tested positive in nested PCR (10/115), while no samples were positive in wet mount microscopy (0/115) (P < 0.01). Among the ten positive specimens, two were identified as Tetratrichomonas spp. and the other eight as Trichomonas tenax in phylogenetic analysis. CONCLUSIONS: Nested PCR is an effective way to detect trichomonads in bronchoalveolar lavage fluid.

Tetratrichomonas in pyopneumothorax.

Pleural trichomonosis is clinically rare, and very few cases of trichomonal empyema have been reported so far. A rare case of an 81-year-old woman with pyopeumothorax presenting with recurrent fever and macroscopic pyuria was present. Microscopic examination of the pleural effusion showed mobile flagellated protozoa which molecular methods identified as Tetratrichomonas. In addition, Streptococcus anginosus was discovered in pleural fluid cultures. Treatment with imipenem/cilastatin and metronidazole successfully eliminated the pathogens and led to relief of clinical symptoms. In the context of a review of the relevant literature, the clinical application of molecular methods in the diagnosis of pleural trichomonosis is underlined.

Cytological studies on the infection of rice root by Ustilaginoidea virens.

In recent years, false smut disease of rice has been one of the most important diseases of cultivated rice in China. Ustilaginoidea virens is an ascomycete fungal pathogen that causes false smut in rice. There is always controversy about whether the pathogen can infect the rice root and cause the occurrence of false smut, mainly due to lack direct cytological evidence. In our study, we observed the cytological structure of rice root invaded by U. virens. The results showed that U. virens could attach to the surface of young roots and penetrate into the intercellular space of the root epidermis. The cellulose microfibrils in root epidermal cell wall are very loose and soft, and their structural features are similar to filaments of rice. After the fungus infected the roots, a large number of fungal secretions were accumulated outside of the cell walls. At 40 days, the fungus began to degrade, but pathogens still had not infected the sclerenchyma, in which the cells are arranged densely and the cell walls are thicker. U. virens could not cross the sclerenchyma layer into the endodermis and phloem of the root. To some extent, the U. virens infection affected the leaf and root growth of the rice. After inoculation, there was no fungal mycelium found in transverse sections of the rice young stem. These results suggested that root colonization of U. virens does not lead to systemic invasion in rice.

Low expression lncRNA RPLP0P2 is associated with poor prognosis and decreased cell proliferation and adhesion ability in lung adenocarcinoma.

We investigated the clinical roles and biological function of long non-coding (lncRNA) RPLP0P2 in lung adenocarcinoma (LAD). The expression level of RPLP0P2 was estimated by quantitative reverse transcription-polymerase chain reaction (qPCR) in 57 pairs of LAD and NT samples and the relation of RPLP0P2 to clinical data of LAD patients was analyzed. We overexpressed RPLP0P2 based on the human LAD cell line A549 by lentivirus­mediated technology, then oncological behavior change was observed of A549 cells and the change of mRNA level of LRRC10B and RPLP0P2 by qPCR. We found that RPLP0P2 expression was lower while LRRC10B mRNA level was higher in LAD than NT by qPCR. RPLP0P2 expression level was negative correlated to LRRC10B mRNA level (Pearson correlation =­0.754, P=0.0021). The expression of RPLP0P2 in lymph node metastasis of LAD group was significantly lower than LAD without lymph node metastasis group. Survival analysis showed that survival time of high expression of RPLP0P2 was significantly longer than low RPLP0P2 level in LAD patients. After RPLP0P2 was overexpressed, the proliferation rate, adhesion ability, S phase and G2/M phase cells and LRRC10B mRNA significantly reduced, while apoptosis and G0/G1 phase cells obviously increased, but migration ability and invasion did not significantly change. Our study ascertained that low expression of RPLP0P2 in LAD is associated with poor prognosis and decreased proliferation and adhesion ability of tumor cells. LRRC10B may be a downstream gene regulated by RPLP0P2.

Villosiclava virens infects specifically rice and barley stamen filaments due to the unique host cell walls.

Rice false smut, caused by the fungal pathogen Villosiclava virens, is one of the most important rice diseases in the world. Previous studies reported that the pathogen has less number of cell wall-degraded genes and attacks dominantly rice stamen filaments and extends intercellularly. To reveal why the fungus infects plant stamen filaments, inoculation test on barley was carried out with the similar protocol to rice. The experimental results showed that the fungus could penetrate quickly into barley stamen filaments and extends both intracellularly and intercellularly, usually resulting in severe damage of the stamen filament tissues. It also attacked young barley lodicules and grew intercellularly by chance. The light microscopic observations found that the epidermal and cortex cells in barley stamen filaments arranged loosely with very thick cell walls and large cell gaps. Cellulose microfibrils in barley stamen filament cell walls arranged very sparsely so that the cell walls looked like transparent. The cell walls were very soft and flexible, and often folded. However, V. virens extended dominantly in the noncellulose regions and seemed never to degrade microfibrils in barley and rice cell walls. This suggested that the unique structures of rice and barley stamen filaments should be fit for their function of elongation in anthesis, and also endow with the susceptibility to the fungus, V. virens.

Distinctive origin of artemisinin-resistant Plasmodium falciparum on the China-Myanmar border.

The artemisinin (ART), discovered in China, has been widely used against malaria in China over the last 30 years. Understanding the emergence and origin of ART resistance in China is therefore of great interest. We analyzed 111 culture-adapted isolates of P. falciparum from China-Myanmar (CM) border for their susceptibility to dihydroartemisinin using the ring stage survival assay (RSA0-3h) and genotyped their K13 genes. Of the isolates, 59 had a wild type of the K13 marker and a median ring survival rate of 0.26% (P95 = 1.005%). Among the remaining isolates harboring single mutations in the K13 marker, 26 survived at >P95(median survival rate = 2.95%). Further, we genotyped the K13 gene of 693 isolates collected from different regions in China and China-Myanmar/Thai-Cambodia/Thai-Myanmar (CM/TC/TM) borders, 308 (44.4%) had K13 mutations and marked differences in the patterns of K13 mutations were observed between the CM and the TC/TM borders. A network diagram showed that majority of the K13 mutant alleles from the CM border clustered together including those harboring the high resistant-associated R539T mutations. The resistant parasites carrying distinct halplotypes suggested the multiple indigenous origins of the resistant alleles, which highlight the importance of surveillance of resistance in all malaria endemic areas where ART has been introduced.

Specific adaptation of Ustilaginoidea virens in occupying host florets revealed by comparative and functional genomics.

Ustilaginoidea virens (Cooke) Takah is an ascomycetous fungus that causes rice false smut, a devastating emerging disease worldwide. Here we report a 39.4 Mb draft genome sequence of U. virens that encodes 8,426 predicted genes. The genome has ~25% repetitive sequences that have been affected by repeat-induced point mutations. Evolutionarily, U. virens is close to the entomopathogenic Metarhizium spp., suggesting potential host jumping across kingdoms. U. virens possesses reduced gene inventories for polysaccharide degradation, nutrient uptake and secondary metabolism, which may result from adaptations to the specific floret infection and biotrophic lifestyles. Consistent with their potential roles in pathogenicity, genes for secreted proteins and secondary metabolism and the pathogen-host interaction database genes are highly enriched in the transcriptome during early infection. We further show that 18 candidate effectors can suppress plant hypersensitive responses. Together, our analyses offer new insights into molecular mechanisms of evolution, biotrophy and pathogenesis of U. virens.

Co-expression of RCH10 and AGLU1 confers rice resistance to fungal sheath blight Rhizoctonia solani and blast Magnorpathe oryzae and reveals impact on seed germination.

Rice sheath blight and blast caused by Rhizoctonia solani Kühn and Magnorpathe oryzae respectively, are the two most destructive fungal diseases in rice. With no genetic natural traits conferring resistance to sheath blight, transgenic manipulation provides an obvious approach. In this study, the rice basic chitinase gene (RCH10) and the alfalfa ß-1,3-glucanase gene (AGLU1) were tandemly inserted into transformation vector pBI101 under the control of 35S promoter with its enhancer sequence to generate a double-defense gene expression cassette pZ100. The pZ100 cassette was transformed into rice (cv. Taipei 309) by Agrobacterium-mediated transformation. More than 160 independent transformants were obtained and confirmed by PCR. Northern analysis of inheritable progenies revealed similar levels of both RCH10 and AGLU1 transcripts in the same individuals. Disease resistance to both sheath blight and blast was challenged in open field inoculation. Immunogold detection revealed that RCH10 and AGLU1 proteins were initially located mainly in the chloroplasts and were delivered to the vacuole and cell wall upon infection, suggesting that these subcellular compartments act as the gathering and execution site for these anti-fungal proteins. We also observed that transgenic seeds display lower germination rate and seedling vigor, indicating that defense enhancement might be achieved at the expense of development.

Wheat gene TaS3 contributes to powdery mildew susceptibility.

KEY MESSAGE: Identification of TaS3 as a potential susceptibility gene encoding a protein homologous to ULP1 protease in wheat, which may regulate SUMO function facilitating powdery mildew attack. Some plant genes that are required for susceptibilities to certain pathogens are known as susceptibility genes or susceptibility factors, whose loss-of-function mutations can confer the plants resistances. To identify potential susceptibility genes to powdery mildew in wheat, differentially expressed genes in compatible and incompatible interactions between wheat and powdery mildew were examined by the cDNA chip assay. The genes exclusively expressed in the susceptible cultivar were interfered using biolistic transient transformation in wheat epidermal cells. The suppression of gene TaS3 (Triticum aestivum susceptibility) decreased the pathogen penetration by 19%, and its over-expression increased the disease susceptibility. The deduced protein from TaS3 belongs to the putative ubiquitin-like protease 1 peptidase domain family. Subcellular localization studies revealed that its protein was accumulated in the nucleus. Quantitative real-time polymerase chain reaction analysis revealed that TaS3 transcript was significantly induced in the compatible host. This suggests that TaS3 is a potential susceptible gene and its function may be related to regulate SUMO functions.

Genetic transformation of cotton with a harpin-encoding gene hpaXoo confers an enhanced defense response against different pathogens through a priming mechanism.

BACKGROUND: The soil-borne fungal pathogen Verticillium dahliae Kleb causes Verticillium wilt in a wide range of crops including cotton (Gossypium hirsutum). To date, most upland cotton varieties are susceptible to V. dahliae and the breeding for cotton varieties with the resistance to Verticillium wilt has not been successful. RESULTS: Hpa1Xoo is a harpin protein from Xanthomonas oryzae pv. oryzae which induces the hypersensitive cell death in plants. When hpa1Xoo was transformed into the susceptible cotton line Z35 through Agrobacterium-mediated transformation, the transgenic cotton line (T-34) with an improved resistance to Verticillium dahliae was obtained. Cells of the transgenic T-34, when mixed with the conidia suspension of V. dahliae, had a higher tolerance to V. dahliae compared to cells of untransformed Z35. Cells of T-34 were more viable 12 h after mixing with V. dahliae conidia suspension. Immunocytological analysis showed that Hpa1Xoo, expressed in T-34, accumulated as clustered particles along the cell walls of T-34. In response to the infection caused by V. dahliae, the microscopic cell death and the generation of reactive oxygen intermediates were observed in leaves of T-34 and these responses were absent in leaves of Z35 inoculated with V. dahliae. Quantitative RT-PCR analysis indicated that five defense-related genes, ghAOX1, hin1, npr1, ghdhg-OMT, and hsr203J, were up-regulated in T-34 inoculated with V. dahliae. The up-regulations of these defense-relate genes were not observed or in a less extent in leaves of Z-35 after the inoculation. CONCLUSIONS: Hpa1Xoo accumulates along the cell walls of the transgenic T-34, where it triggers the generation of H2O2 as an endogenous elicitor. T-34 is thus in a primed state, ready to protect the host from the pathogen. The results of this study suggest that the transformation of cotton with hpa1Xoo could be an effective approach for the development of cotton varieties with the improved resistance against soil-borne pathogens.

Identification of Colletotrichum spp. isolated from strawberry in Zhejiang Province and Shanghai City, China.

Strawberry anthracnose, caused by Colletotrichum spp., is a major disease of cultivated strawberry. This study identifies 31 isolates of Colletotrichum spp. which cause strawberry anthracnose in Zhejiang Province and Shanghai City, China. Eleven isolates were identified as C. acutatum, 10 as C. gloeosporioides and 10 as C. fragariae based on morphological characteristics, phylogenetic and sequence analyses. Species-specific polymerase chain reaction (PCR) and enzyme digestion further confirmed the identification of the Colletotrichum spp., demonstrating that these three species are currently the causal agents of strawberry anthracnose in the studied regions. Based on analysis of rDNA internal transcribed spacers (ITS) sequences, sequences of all C. acutatum were identical, and little genetic variability was observed between C. fragariae and C. gloeosporioides. However, the conservative nature of the MvnI specific site from isolates of C. gloeosporioides was confirmed, and this site could be used to differentiate C. gloeosporioides from C. fragariae.

[Ultrastructural observation related to cell-to-cell movement and long-distance systemic transport on the hosts infected with BBWV 2].

The alteration of ultrastructure in Pisum sativum and Vicia faba leaf cells infected with B935 isolate of BBWV 2 were investigated by electron microscopy, immunogold-labeling technique. The results showed that the membranous proliferation, virus-formed crystals and tubular structures were found in leaf cells of two hosts. At early stages of infection, the tubules containing virus-like particles associate with plasmodesmata in mesophyll cell. Immunogold particles anti-BBWV 2 were localized to the plasmodesmata modified by tubules passing through them. The membranous proliferation and virus-formed tubules were also found in the parenchyma cells, companion cells and transfer cells of vascular bundle. Some virus-like particles located within sieve tube can be labeled immunogold particles anti-BBWV 2. These suggest that BBWV 2, similar CPMV, produce tubules extending into the plasmodesmata. Virions assembled in the cytoplasm are escorted to the tubular structures through interactions with their MP and are then transported to the adjacent cell. Many 160 nm in diameter virus-formed tubules in the cytoplasm, as a special aggregate, not directly relate to cell-to-cell movement; Intact virions are long-distance sustemic transported possibly through sieve elements.

A Begomovirus DNAbeta-encoded protein binds DNA, functions as a suppressor of RNA silencing, and targets the cell nucleus.

Our previous results demonstrated that the DNAbeta satellite (Y10beta) associated with Tomato yellow leaf curl China virus Y10 isolate (TYLCCNV-Y10) is essential for induction of leaf curl symptoms in plants and that transgenic expression of its betaC1 gene in Nicotiana plants induces virus-like symptoms. In the present study, in vitro DNA binding activity of the betaC1 proteins of Y10beta and DNAbeta (Y35beta) found in the Tobacco curly shoot virus Y35 isolate (TbCSV-Y35) were studied following their expression as six-His fusion proteins in Escherichia coli. Electrophoretic mobility shift assays and UV cross-linking experiments revealed that betaC1 proteins could bind both single-stranded and double-stranded DNA without size or sequence specificity. Suppression of green fluorescent protein (GFP) transgene silencing was observed with the new leaves of GFP-expressing Nicotiana benthamiana plants coinoculated by TYLCCNV-Y10 plus Y10beta or by TbCSV-Y35 plus Y35beta. In a patch agroinfiltration assay, the transiently expressed betaC1 gene of Y10beta or Y35beta was able to suppress host RNA silencing activities and permitted the accumulation of high levels of GFP mRNA in the infiltrated leaf patches of GFP transgenic N. benthamiana plants. The betaC1 protein of Y10beta accumulated primarily in the nuclei of plant and insect cells when fused with beta-glucuronidase or GFP and immunogold labeling showed that the betaC1 protein is present in the nuclei of infected N. benthamiana plants. A mutant version of Y10beta carrying the mutations within the putative nuclear localization sequence of the Y10 betaC1 protein failed to induce disease symptoms, suppress RNA silencing, or accumulate in the nucleus, suggesting that nuclear localization of the betaC1 protein is a key requirement for symptom induction and silencing suppression.

Expression of a begomoviral DNAbeta gene in transgenic Nicotiana plants induced abnormal cell division.

An increasing number of monopartite begomoviruses are being identified that a satellite molecule (DNAbeta) is required to induce typical symptoms in host plants. DNAbeta encodes a single gene (termed betaC1) encoded in the complementary-sense. We have produced transgenic Nicotiana benthamiana and N. tabacum plants expressing the betaC1 gene of a DNAbeta associated with Tomato yellow leaf curl China virus (TYLCCNV), under the control of the Cauliflower mosaic virus 35S promoter. Transgenic plants expressing betaC1 showed severe developmental abnormalities in both species. Microscopic analysis of sections of both transgenic and non-transgenic N. tabacum leaves showed abnormal outgrowths of transgenic N. tabacum to be due to disorganized cell division (hyperplasia) of spongy and palisade parenchyma. Immuno-gold labeling of sections with a polyclonal antibody against the betaC1 protein showed that the betaC1 protein accumulated in the nuclei of cells. The possible biological function of the betaC1 protein was discussed.

The symptom difference induced by tobacco mosaic virus and tomato mosaic virus in tobacco plants containing the N gene is determined by movement protein gene.

Tobacco mosaic virus (TMV) and Tomato mosaic virus (ToMV) are two closely related viruses in the genus Tobamovirus, but they induce obviously different sizes of necrotic lesions in tobacco plants containing the N gene. Comparison of the symptoms produced by TMV, ToMV and a chimaeric virus (T/OMP), in which the TMV movement protein (MP) gene was replaced by the ToMV MP gene, showed T/OMP caused necrotic lesions that were similar in size to those of ToMV in tobacco plants containing the N gene. The coat protein and MP of the three viruses accumulated in planta with similar levels, and the replication level of TMV and T/OMP in protoplasts also had no difference. Comparison of the activities of defense-related enzymes (PAL, POD and PPO) induced by the three viruses also showed that the variability of enzyme activity induced by T/OMP was similar to that induced by TMV, but different from that induced by ToMV. The results indicate that the size difference of necrotic lesions induced by TMV and ToMV in tobacco plants containing the N gene results from the functional difference of their MP genes.