International team shows how newly identified alphasatellite affects aphid transmission of lethal banana virus
Banana bunchy top virus, (BBTV) spread by banana aphids, is the most serious disease affecting bananas and plantains. In areas where bananas are grown, the disease can be devastating to the local economy as once infected, the plants don't recover.
Banana bunchy top virus, (BBTV) spread by banana aphids, is the most serious disease affecting bananas and plantains. In areas where bananas are grown, the disease can be devastating to the local economy as once infected, the plants don't recover.
An international group of scientists studying banana bunchy top disease (BBTD) looked in detail at a newly emerging alphasatellite, a single-stranded part of DNA that requires a helper virus for disease transmission.
Their work appears in the peer-reviewed open-access medical journal PLOS Pathogens, April 12.
The researchers identified a new alphasatellite in BBTV from the Democratic Republic of the Congo (DRC). In a series of experiments, they identified special features of this alphasatellite, suggesting that it is a new genus. "The impacts of alphasatellites on BBTV infection and disease transmission by aphids have not been studied so far," they write.
BBTD was first recorded in 1889 in Fiji, in the South Pacific, and is thought to have originated in Southeast Asia. The disease is though to have been exported between 7,000 and 10,000 years ago, when banana domestication occurred in tropical areas. The researchers note that the BBTV isolates from Southeast Asia "are frequently associated with alphasatellites." These alphasatellites depend upon the BBTV as a helper virus to infect plants.
The DRC was one of the first sub-Saharan countries where BBTD was introduced, and was first reported there in 1958.
Special features
One of the special features of this alphasatellite is that although the aphids that transmit BBTV have so far been restricted to infecting monocots, the new genus they found was related to alphasatellites of nanoviruses that infect dicots. Monocots, such as grasses, and dicots, such as many fruits, have distinctly different leaves, stems, roots and flowers. They say, “we demonstrate that BBTV and alphasatellite clones can infect the dicot N. benthamiana, followed by recovery and symptomless persistence of the alphasatellite.”
The researchers also report that the new alphasatellite DNA was enclosed by BBTV coat protein and accumulated at high levels in plants and aphids. This had an interesting effect. They observed that the alphasatellite reduces BBTC accumulation in banana plants and aphids and interferes with virus transmission by aphids.
Molecular analysis of the virus-infected banana plants "revealed new features of viral DNA transcription and siRNA biogenesis, both affected by alphasatellite," they report.
Results and more questions
The experiments evaluated the effect of the new alphasatellite on on BBTV disease development. The researchers found that "median loads of all BBTV components were reduced in the presence of alphasatellite, thereby resulting in a ~25% decrease of the median load of total helper virus DNA." The median loads of BBTV components were also reduced when alphasatellite was present in aphids, resulting in a ~40% decrease of total helper DNA.
The researchers raise many questions for further investigation regarding the costs and benefits of alphasatellites and the possibility that alphasatellites can move from one helper virus to another in order to expand their range of host plants.
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V. Guyot et al. "A newly emerging alphasatellite affects banana bunchy top virus replication, transcription, siRNA production and transmission by aphids." PLOS Pathogens, April 12, 2022.
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