Helicoverpa armigera densovirus 1

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Classification

Higher order Taxa

Viruses (+ ssDNA virus); Shotokuvirae; Cossaviricota; Quintoviricetes; Piccovirales; Parvoviridae; Densovirus; Iteradensovirus

Species

NCBI: Helicoverpa armigera densovirus 1 Taxonomy [1]

Helicoverpa armigera densovirus (genus), HaDNV1 (species)

Image of the cotton bollworm eating a cotton plant by BioChemTech based in Chinisau Moldova.

Helicoverpa armigera densovirus (HaDNV-1) is a single stranded DNA virus that consists of the mutualism between the cotton bollworm (H. armigera) and a densovirus. A non-infected strain of H. armigera is a crop pest that feeds on agricultural resources, such as cotton, corn, rice, tomato, chickpea, etc. An infected strain of the cotton bollworm does the same, however at a greater effect. The densovirus directly increases the early growth rate of H. armigera and in effect, increases the overall fitness of the organism. In addition, densoviruses protect H. armigera from biopesticides like Bt toxin, which makes the cotton bollworm a more harmful organism to the environment as it can continue to feed on crops while being resistant to biological pesticides. This polyphagous, migratory species can be found in a number of areas, with its native home being Australia and Oceania, it can also be found in Brazil and the Caribbean. Since H. armigera depends on crops on survival, its habitat is based on largely horticultural areas where it can feed on more than 120 plant species in the appropriate climate.

Genome Structure

Helicoverpa armigera densovirus is a small icosahedral virus ranging from 4 to 6 kilobases. However, the size and organization of densovirus vary and given their structure, they can be classified into three different groups. The first group corresponds to densoviruses, like HaDNV-1 that have inverted terminal repeats on the DNA strand. Additionally, these viruses have an ambisense structure, meaning that both nonstructural (NS) and structural (VP) proteins are found on the starting 5' end of the DNA strand. On the other hand, viruses that belong to the Iteravirus or Brevidensovirus are monosense which suggests that the NS and VP proteins can be found at both the starting 5' end and the 3' end of the DNA strand.

Image of the ambisense and monosense DNA structure of the densovirus by Vivek Prasad and Shalini Srivastava (Ecofriendly Pest Management for Food Security).

Cell Structure, Metabolism and Life Cycle

HaDNV-1 is a novel member of the genus Iteradensovirus. It is 18-26nm in diameter, non enveloped, and has an Icosahedral shaped structure.

For the metabolism of H. armigera, it mainly utilizes the Cotton Bollworm larvae metabolic processes. This is a theoretical symbiosis although and more research needs to be done. The virus gets to use the product from metabolism and the larvae get the benefits. The virus does not shut down host metabolism like most pathogenic viruses do. H. armigera are O2 consumers and take part in aerobic respiration. They produce CO2, carbohydrates, and lipids.

The life cycle of the virus starts with a viron attaching itself to a host membrane. Next it disassemblies itself and enters the cell via endocytosis. It then undergoes a compliment, bilateral transcription in two different directions, then transcription, RCR, and finally gets sent to another cell or undergoes compliment and starts the cycle over again. The life cycle of H. armigera has four stages: egg stage, larva stage, pupa stage, and adult stage. The incubation time from egg to larva is 2-5 days. Development time from larva to pupa is 15-23 days. The pupal period is 6 days. The oviposition is 5-24 days. It relies on a S phase cell cycle and had autonomous replication taking place.

Image of the life cycle of a single-stranded DNA virus by Dr. Mikhail Pooggin. Myriapoda.

Ecology and Pathogenesis

Image of the bollworm moth larvae eating a cotton plant by Dr. Yanhui and Professor Wu from Lancaster University. Myriapoda.

The Helicoverpa armigera densovirus HaDNV-1 (HaDNV-1) lives within its mutualist symbiont, the cotton bollworm moth (Helicoverpa armigera) larvae and pupa. H. armigera resides on the cotton plant and other crops throughout Asia, Africa, and Australasia. HaDNV-1 provides the moth larvae and pupa with an increased development rate, female longevity and fecundity, and protects the larvae from the baculovirus biopesticide, Helicoverpa armigera nucleopolyhedrovirus (HaNPV). HaDNV-1 possibly aids in H. armigera's tolerance of the baculovirus Cry1Ac toxin in bollworm strains that are susceptible to biopesticide. Cry1Ac is responsible for forming pores in the cell membrane by interacting with APN and ABC transporters on the cell membrane surface. The pores formed ultimately result in the death of the insect. Farmers are now trying to utilize new techniques to limit bollworm moth infestation of various plants due to this rising resistance to biopesticides through an unknown mechanism at this time. The newly discovered symbiosis of HaDNV-1 and H. armigera poses new threats to the cotton industry.

References

1. Bravo, A., Gill, S. S., & Soberón, M. "Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control". Toxicon: official journal of the International Society on Toxinology. 2007. Volume 49. p. 423–435.

2. Xu P., Graham, R. I., Wilson, K., & Wu, K. "Structure and transcription of the Helicoverpa armigera densovirus (HaDV2) genome and its expression strategy in LD652 cells". Virology Journal. 2017. Volume 14.

3. Xu, P., Liu, Y., Graham, R. I., Wilson, K., & Wu, K. "Densovirus is a mutualistic symbiont of a global crop pest (helicoverpa armigera) and protects against a baculovirus and BT Biopesticide". PLoS Pathogens. 2014. Volume 10.

4. Ecosostenibile. (2021, June 30). (Italiano) helicoverpa armigera: Sistematica, habitat, Ciclo Biologico, lotta ... Un Mondo Ecosostenibile. Retrieved April 25, 2022, from https://antropocene.it/en/2021/06/30/helicoverpa-armigera/

5. ScienceDirect. (2016). Densovirus. Densovirus - an overview | ScienceDirect Topics. Retrieved April 25, 2022, from https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/densovirus#:~:text=Densoviruses%20(DNVs)%20are%20small%20icosahedral,counterparts%2C%20in%20the%20family%20Parvoviridae

6. Pooggin, M. How can plant DNA viruses evade Sirna-directed DNA methylation and silencing? International Journal of Molecular Sciences. 2013. Volume 14. p. 15233–15259.

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Author

Page authored by Abigael Frederick, David Duncan, and Bradley Enneking, students of Prof. Jay Lennon at Indiana University.