Severe Stunting Symptoms upon Nepovirus Infection Are Reminiscent of a Chronic Hypersensitive-Like Response in a Perennial Woody Fruit Crop

Virus infection of plants can result in various degrees of detrimental impacts and disparate symptom types and severities. Although great strides have been made in our understanding of the virus–host interactions in herbaceous model plants, the mechanisms underlying symptom development are poorly understood in perennial fruit crops. Grapevine fanleaf virus (GFLV) causes variable symptoms in most vineyards worldwide. To better understand GFLV-grapevine interactions in relation to symptom development, field and greenhouse trials were conducted with a grapevine genotype that exhibits distinct symptoms in response to a severe and a mild strain of GFLV. After validation of the infection status of the experimental vines by high-throughput sequencing, the transcriptomic and metabolomic profiles in plants infected with the two viral strains were tested and compared by RNA-Seq and LC-MS, respectively, in the differentiating grapevine genotype. In vines infected with the severe GFLV strain, 1023 genes, among which some are implicated in the regulation of the hypersensitive-type response, were specifically deregulated, and a higher accumulation of resveratrol and phytohormones was observed. Interestingly, some experimental vines restricted the virus to the rootstock and remained symptomless. Our results suggest that GFLV induces a strain- and cultivar-specific defense reaction similar to a hypersensitive reaction. This type of defense leads to a severe stunting phenotype in some grapevines, whereas others are resistant. This work is the first evidence of a hypersensitive-like reaction in grapevine during virus infection.

Generation of mild recombinants of papaya ringspot virus to minimize the problem of strain-specific cross protection

Papaya ringspot virus (PRSV) causes severe damage to papaya (Carica papaya L.) and is the primary limiting factor for papaya production worldwide. A nitrous acid-induced mild strain PRSV HA 5-1, derived from Hawaii strain HA, has been applied to control PRSV by cross protection for decades. However, the problem of strain-specific protection hampers its application in Taiwan and other geographic regions outside Hawaii. Here, sequence comparison of the genomic sequence of HA 5-1 with that of HA revealed 69 nucleotide changes, resulting in 31 aa changes in which 16 aa are structurally different. The multiple mutations of HA 5-1 are considered resulting from nitrous-acid induction since 86% of nucleotide changes are transition mutations. The stable HA 5-1 was used as a backbone to generate recombinants carrying individual 3’ fragments of Vietnam severe strain TG5, including NIa, NIb, and CP3’ regions, individually or in combination. Our results indicated that the best heterologous fragment for the recombinant is the region of CP3’, with which symptom attenuation of the recombinant is like that of HA 5-1. This mild recombinant HA51/TG5-CP3’ retained high levels of protection against the homologous HA in papaya plants and significantly increased the protection against the heterologous TG-5. Similarly, HA 5-1 recombinants carrying individual CP3’ fragments from Thailand SMK, Taiwan YK, and Vietnam ST2 severe strains also significantly increase the protection against the corresponding heterologous strains in papaya plants. Thus, our recombinant approach for mild strain generation is a fast and effective way to minimize the problem of strain-specific protection.

Complete Genome Sequence of Isolate Bari 1, a Mild Strain of Cauliflower Mosaic Virus

We present here the complete genome sequence of isolate Bari 1, a mild strain of Cauliflower mosaic virus (CaMV). The isolate was collected from Diplotaxis tenuifolia (perennial wall-rocket) in Bari, Italy. The genome was 8,020 nucleotides long and shared ≤85.4% nucleotide identity to other CaMV isolates.

DIAGNOSIS OF THE FUNCTIONAL STATE OF AUTONOMIC REGULATION AND PROGNOSIS OF MALADAPTATION DEVELOPMENT

It was demonstrated that medical students with vagotonia and sympathicotonia had a mild strain of their regulation mechanisms. The considerable signs of autonomic regulation inefficiency were found out in conditions of physical exercising. The adaptation of individuals with vagotonia to the physical loading was going mainly due to the excessive elevation of heart rate along with the increase in diastolic blood pressure. In contrast, abnormal elevation of pulse pressure after physical loading was observed in young people with sympathicotonia, which is concerned as a negative prognosis and also a predictor of arterial hypertension. Some physiological aspects of the recovery period confirmed the insufficiency of autonomic regulation as well as discoordination of the reciprocal departments of autonomic nervous system in examined persons. The unfavorable range of increase in hemodynamic parameters after physical loading was to pioneer. The following ranges of cardiovascular indexes indicated the mild level of maladaptation: in individuals with vagotonia – Mean Arterial Pressure by 6-30%, heart rate by 80-120%, endurance coefficient – 5-27%, and Robinson’s index – 121–200%; in persons with sympathicotonia – endurance coefficient – 5-27%, and Pulse Pressure – 75-105%. These changes have to be corrected in advance for the prophylactics of specific and nonspecific complications of visceral systems functioning. The economical effectiveness of this research is accomplished by the reduction of financial expenses because of prophylactics and/or diagnosis of autonomic deregulation development

A Double Mutation in the Conserved Motifs of the Helper Component Protease of Papaya Leaf Distortion Mosaic Virus for the Generation of a Cross-Protective Attenuated Strain

Potyviral helper component protease (HC-Pro), as a major determinant of symptom expression in susceptible plants, is a likely target candidate in the production of attenuated strains for cross-protection. In this study, single or double mutations of Lys (K) to Glu (E) in the Lys-Ile-Thr-Cys motif and Arg (R) to Ile (I) in the Phe-Arg-Asn-Lys motif of the HC-Pro from the severe papaya leaf distortion mosaic virus strain DF (PLDMV-DF) reduced symptom expression and virus accumulation in infected papaya (Carica papaya) plants. The papaya plants infected with the attenuated double mutant of PLDMV-EI presented as symptomless. PLDMV-EI provided effective protection against PLDMV-DF infection in three papaya cultivars and had no effect on plant growth and development. Our result showed that PLDMV-EI is a promising mild strain for the practical use of cross-protection in the field.

Spatiotemporal Spread of Cacao Swollen Shoot Virus Severe Strain 1A in Mixed Hybrid Cacao Pre-inoculated With Mild Strain N1

The spatiotemporal spread of cocoa swollen shoot virus disease (CSSVD), which is caused by cacao swollen shoot virus (CSSV) severe strain 1A in mixed hybrid cacao pre-inoculated with CSSV mild strain N1 (CSSV-N1), was investigated during a field experiment from 2006 to 2017, at the Cocoa Research Institute of Ghana. The development of disease epidemics has been described by the use of statistical modeling. Protecting all cacao plants with CSSV-N1 reduced the rate of CSSV-1A symptom appearance by 43% (P = 0.05) compared with the nonprotected control and by 33% compared with plots where cacao plants in the outer three or five rows were protected with CSSV-N1. Similarly, creating the protective outer rings three or five rows deep reduced the rate of CSSV-1A symptoms by 14% (P = 0.05) compared with the nonprotected control. CSSV-1A epidemics increased approximately 18% faster (P = 0.05) in transects oriented from the north and east compared with those oriented from the south and west. During the last 2 years of the study, CSSVD spread decreased significantly (P = 0.05) faster in plots where all test cacao plants were inoculated with CSSV-N1 compared with other treatments. The growth of cacao did not differ significantly among the treatments over the 9-year assessment period. Similarly, differences in the cumulative yield among the treatments over the 8-year assessment period were not significant.

Identification of Key Residues Required for RNA Silencing Suppressor Activity of p23 Protein from a Mild Strain of Citrus Tristeza Virus

The severe strain of citrus tristeza virus (CTV) causes quick decline of citrus trees. However, the CTV mild strain causes no symptoms and commonly presents in citrus trees. Viral suppressor of RNA silencing (VSR) plays an important role in the successful invasion of viruses into plants. For CTV, VSR has mostly been studied in severe strains. In this study, the N4 mild strain in China was sequenced and found to have high sequence identity with the T30 strain. Furthermore, we verified the functions of three VSRs in the N4 strain, and p23 was found to be the most effective in terms of local silencing suppressor activity among the three CTV VSRs and localized to both nucleus and plasmodesmata, which is similar to CTV T36 strain. Several conserved amino acids were identified in p23. Mutation of E95A/V96A and M99A/L100AA impaired p23 protein stability. Consequently, these two mutants lost most of its suppressor activity and their protein levels could not be rescued by co-expressing p19. Q93A and R143A/E144A abolished p23 suppressor activity only and their protein levels increased to wild type level when co-expressed with p19. This work may facilitate a better understanding of the pathogenic mechanism of CTV mild strains.

A New Era for Mild Strain Cross-Protection

Societal and environmental pressures demand high-quality and resilient cropping plants and plant-based foods grown with the use of low or no synthetic chemical inputs. Mild strain cross-protection (MSCP), the pre-immunization of a plant using a mild strain of a virus to protect against subsequent infection by a severe strain of the virus, fits with future-proofing of production systems. New examples of MSCP use have occurred recently. New technologies are converging to support the discovery and mechanism(s) of action of MSCP strains thereby accelerating the popularity of their use.