In a new literature review published in the Trends in Plant Science journal, VIRTIGATION partner CSIC unveils the secrets of success of whitefly-transmitted begomoviruses like ToLCNDV and TYLCV.
A very successful group of emerging plant viruses
Begomoviruses, which belong to the Geminiviridae family, are an extremely successful group of emerging plant viruses that have wreaked havoc on tomato and cucurbit crops worldwide. The International Committee on Taxonomy of Viruses recognises 445 species of begomoviruses – the largest in the entire Virosphere. They are transmitted by the Bemisia tabaci sensu lato, a complex of more than 40 morphologically indistinguishable whitefly species. Begomoviruses are responsible for a wide variety of symptoms in the hosts, including mosaics, mottles, yellowing, leaf curling and/or deformation, reduction in plant growth, and deformation in a decreased number of fruits. They can cause total loss of crop production, thus devastating both open field and greenhouse crops across the globe. Not only tomatoes and cucurbits, but also root and fiber crops fall victim to Begomoviruses and the diseases they cause. For tomato and cucurbit crops, especially begomoviruses like ToLCNDV, but also TYLCV constitute a major threat.
Recombination & DNA satellites as key success factors
The genomes of begomoviruses, like all other geminiviruses, are encapsidated in twinned (geminate) virions. Genomes are composed of one (i.e. monopartite) or two (i.e. bipartite, DNA-A and DNA-B) circular single-stranded DNA (ssDNA) molecules. The genomes of begomoviruses can be associated with circular ssDNA satellite molecules, i.e. alphasatellites, betasatellites, and deltasatellites. Begomoviruses are typically replicated via a rolling-circle replication mechanism, but also via a recombination-dependent replication mechanism. As for other viruses and all living things, begomoviruses benefit in their evolution from three major forces: mutation, recombination, and pseudo-recombination (reassortment).
The CSIC researchers highlight in particular the key role of recombination in particular in the generation and emergence of new variants, strains, and species. Moreover, recombination increases the potential of begomoviruses to adapt to different host plants and environmental conditions, thus favoring their emergence. A well-known example presented by the CSIC scientists is the tomato yellow leaf curl disease in the Mediterranean basin, which is caused by recombinant viruses that continue to emerge in the field.
In addition to this, DNA satellites are another key success factor mentioned by the CSIC authors in the evolution of begomoviruses. Circular ssDNA satellite molecules often accompany begomovirus infections, which seems to be the result of an intricate interplay in their evolution. Begomoviruses could have recruited the DNA satellites to give them an evolutionary advantage. Alternatively, the satellites could have been able to use helper (begomo-)viruses for their benefit. Especially betasatellites play a key role in the pathogenesis and success of the helper begomoviruses. Most betasatellites enhance the accumulation of the helper viruses, and in some cases they are necessary to induce symptoms.
Whiteflies as supervectors of begomoviruses
The Bemisia tabaci whitefly is able to feed on plants of more than 1000 species belonging to over 100 botanical families. It is included in a list of ‘100 of the world’s worst invasive alien species’. Not only is the Bemisia tabaci whitefly a global plant pest, but also a supervector, as it can transmit viruses belonging to almost 500 species, including begomoviruses. As concerns TYLCV, the role of Bemisia tabaci as supervectors of begomoviruses is even more prominent, according to the VIRTIGATION CSIC investigators. They cite recent findings which show that TYLCV can replicate within the whitefly.
Furthermore, after a Bemisia tabaci has acquired TYLCV, it retains it for its entire lifespan. The lifetime infectivity persistence of TYLCV in the insect could help explain the global spread of this virus in crops like tomatoes. However, according to the CSIC authors, it still remains to be seen whether the phenomenon of replication in the insect is a unique characteristic of TYLCV, or whether it is a more common feature at work also in other begomoviruses.
More info about VIRTIGATION partner CSIC's research
The full version of CSIC’s literature review in the Trends in Plant Science journal titled “Begomoviruses: what is the secret(s) of their success?” is available online here since 15 February 2023. It has been authored by CSIC’s leading scientists in VIRTIGATION, Jesús Navas-Castillo and Elvira Fiallo-Olivé.
Find out more about VIRTIGATION’s scientific publications on our website here.
Disclaimer: There are no underlying datasets for this literature review.
