Molecular characterization of two recombinant isolates of telosma mosaic virus infecting Passiflora edulis from Fujian Province in China

Mutating the arginine residue within the FRNK motif of telosma mosaic virus (TelMV) HC-Pro protein attenuates viral infection and confers effective protection against TelMV in passion fruit (Passiflora edulis)

BACKGROUND

Telosma mosaic virus (TelMV, Potyvirus, Potyviridae) is an emerging viral pathogen that threatens passion fruit plantations worldwide. However, an efficient strategy for controlling such a virus is not yet available. Cross protection is a phenomenon in which pre-infection of a plant with one mild strain prevents or delays subsequent infection by the same or closely related virus. HC-Pro is the potyviral encoded multifunctional protein involved in several steps of viral infection, including multiplication, movement, transmission and RNA silencing suppression. In this study, we tested whether it is possible to generate attenuated viral strains capable of conferring protection against severe TelMV infection by manipulating the HC-Pro gene.

RESULTS

By introducing point mutation into the conserved motif FRNK of HC-Pro that is essential for RNA silencing suppression, we have successfully obtained three attenuated mutants of TelMV (R181K, R181D, and R181E, respectively). These attenuated TelMV mutants could systemically infect passion fruit plants without noticeable symptoms. Pre-inoculation of one of these attenuated mutants confers efficient protection against subsequent infection by severe TelMV strain. Moreover, we demonstrated that the HC-Pros harbored by the attenuated mutants exhibit reduced RNA silencing suppression activity in Nicotiana benthamiana leaves.

CONCLUSION

The attenuated TelMV mutants developed in this study that are suitable for cross protection offer a practical, powerful tool to fight against TelMV for sustainable passion fruit production. © 2024 Society of Chemical Industry.

Synthesis and Screening of Chemical Agents Targeting Viral Protein Genome-Linked Protein of Telosma Mosaic Virus

The viral protein genome-linked protein (VPg) of telosma mosaic virus (TeMV) plays an important role in viral reproduction. In this study, the expression conditions of TeMV VPg were explored. A series of novel benzenesulfonamide derivatives were synthesized. The binding sites of the target compounds and TeMV VPg were studied by molecular docking, and the interaction was verified by microscale thermophoresis. The study revealed that the optimal expression conditions for TeMV VPg were in Escherichia coli Rosetta with IPTG concentration of 0.8 mM and induction temperature of 25 °C. Compounds A4, A6, A9, A16, and A17 exhibited excellent binding affinity to TeMV VPg, with Kd values of 0.23, 0.034, 0.19, 0.086, and 0.22 μM, respectively. LYS 121 is the key amino acid site. Compounds A9 inhibited the expression of TeMV VPg in Nicotiana benthamiana. The results suggested that TeMV VPg is a potential antiviral target to screen anti-TeMV compounds.

Occurrence and Distribution of Major Viruses Infecting Passion Fruit in Guizhou Province, China, and Molecular Characterization of Two Potyviruses

The planting of passion fruit (Passiflora edulis) in Guizhou Province has gradually increased, and the area under cultivation ranks third in China. However, the cultivation and production of passion fruit is severely affected by viral diseases. In 2021 and 2022, we investigated the occurrence of multiple viral diseases in major cultivation areas, identified the main viruses and conducted field surveys in different growing areas of passion fruit in Guizhou Province, China. In total, 308 samples were randomly collected from 10 different passion fruit cultivation areas, and seven viral diseases were identified using electron microscopy, small RNA sequencing, and reverse-transcription polymerase chain reaction. Among them, the infection rate of Telosma mosaic virus (TeMV) was the highest (50%), followed by East Asian Passiflora virus (EAPV) (19%), and cucumber mosaic virus (CMV) (15%). The detection rates of the other four viruses were lower: Passiflora latent virus (PLV) (1%), turnip mosaic virus (TuMV) (0.6%), Passiflora virus Y (PaVY) (0.3%), and Euphorbia leaf curl virus (ELCV) (6%). In addition, high rates of mixed TeMV + CMV + EAPV infections were found in the province. Notably, 79% of EAPV-infected plants were also infected with TeMV. Finally, the molecular characteristics of the two highly detected potyviruses, TeMV and EAPV, were analyzed. To our knowledge, this study is the first systematic survey of viral diseases of passion fruit in Guizhou Province, China.

Passion fruit plants alter the soil microbial community with continuous cropping and improve plant disease resistance by recruiting beneficial microorganisms

Passion fruit (Passiflora edulis) is widely grown in tropical and subtropical regions, showing high economic and ornamental value. Microorganisms are indicators for the stability and health of the soil ecosystem, which can affect the yield and quality of passion fruit under continuous cropping. High-throughput sequencing and interactive analysis were used to analyse the variation of microbial communities in the noncultivated soil (NCS), cultivated soil (CS), and the rhizosphere soil of purple passion fruit (Passiflora edulis f. edulis ×Passiflora edulis f. flavicarpa, RP) and yellow passion fruit (Passiflora edulis f. flavicarpa, RY). An average of 98,001 high-quality fungal internal transcribed spacer (ITS) sequences, mainly from Ascomycota, Basidiomycota, Mortierellomycota, Mucoromycota and Glomeromycota, as well as an average of 71,299 high-quality bacterial 16S rRNA sequences, mainly from Proteobacteria, Actinobacteria, Acidobacteria, Firmicutes and Chloroflexi, were obtained per sample. It was found that the continuous cropping of passion fruit increased the richness but reduced the diversity of soil fungi, while it dramatically increased the richness and diversity of soil bacteria. In addition, during the continuous cropping, grafting different scions in the same rootstock contributed to the aggregation of differential rhizosphere microbial communities. Among fungal genera, Trichoderma showed higher abundance in RY than in RP and CS, while the opposite was observed in the pathogen Fusarium. Moreover, the co-occurrence network and potential function analyses also showed that the appearance of Trichoderma was related to Fusarium and its contribution to plant metabolism was significantly greater in RY than in RP and CS. In conclusion, the rhizosphere of yellow passion fruit may be beneficial for the enrichment of disease-resistant microbes, such as Trichoderma, which may be an important factor inducing stronger resistance to stem rot. It will help to form a potential strategy for overcoming the pathogen-mediated obstacles in passion fruit and improve its yield and quality.

Characterization and Detection of Passiflora Mottle Virus and Two Other Potyviruses Causing Passionfruit Woodiness Disease in Vietnam

Passionfruit plantings in Vietnam increased to 10,000 ha in 2019. However, outbreaks of passionfruit woodiness disease (PWD) have become a serious threat to production. In this study, five virus isolates (DN1, DN4, NA1, GL1, and GL2) were collected from different areas of Vietnam. Their causal roles in PWD were verified by back-inoculation to passionfruit. Analyses of coat protein (CP) and genomic sequences revealed that the GL1 isolate is closely related to East Asia Passiflora virus (EAPV) AO strain of Japan (polyprotein nt and aa identities of 98.1 and 98.2%, respectively), and the GL2 isolate is related to Telosma mosaic virus (TelMV) isolate PasFru, China (polyprotein nt and aa identities of 87.1 and 90.9%, respectively). CP comparison, host range, and cytological characterization indicated that DN1, DN4, and NA1 are potyviruses but are different from EAPV and TelMV. Phylogenic analyses of their CP and genome sequences indicated that these three isolates and the passionfruit severe mottle-associated virus Fujian isolate of China belong to a distinct clade, which does not meet the threshold (76% nt identity of polyprotein) to be regarded as any of potyviral species. Thus, a new species name, Passiflora mottle virus, (PaMoV), has been proposed by the International Committee on Taxonomy of Viruses. A rabbit antiserum was produced against the CP of DN1, and it can distinguish PaMoV from TelMV and EAPV in western blotting and enzyme-linked immunosorbent assay (ELISA) without cross-reactions. Field surveys of 240 samples by ELISA and reverse transcription PCR found that PWD in Vietnam is caused mainly by PaMoV, followed by EAPV, mixed infection of PaMoV and EAPV, and rare cases of TelMV.

Complete genome sequence of passiflora virus Y infecting passion fruit in China

The complete genome sequence of passiflora virus Y (PaVY) from passion fruit growing in Guangdong province, China, was determined. The entire positive single-strand RNA genome comprises 9681 nucleotides (nt) excluding the poly(A) tail and encodes a polyprotein of 3084 amino acids flanked by 5' and 3' untranslated regions of 169 and 257 nt, respectively. In sequence comparisons and phylogenetic analysis, PaVY appears to represent a new species in the bean common mosaic virus subgroup of the genus Potyvirus. This is the first report of the complete genome sequence of PaVY and the first report of this virus in China.