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Plant DNA virus can use host machinary to replicate in its insect vector

2020-07-20

Of 1,000-plus known plant viruses, over 75% are transmitted by aphids, whiteflies, leafhoppers and other insects. However, merely a minority of plant RNA viruses have been confirmed to replicate within their insect vectors in addition to their plant hosts so far. Whether plant DNA viruses have also evolved to replicate in their insect vectors has remained elusive. More importantly, there has been a paucity of research regarding the mechanisms employed by plant viruses to cross the kingdom barrier to duplicate themselves within insect vectors. This question is of immense significance to gaining a more insightful understanding of virus evolution and giving rise to novel approaches to interdicting virus transmission by identifying virus and vector components involved in replication.

Geminiviruses comprise a large family of plant-infecting, single-stranded DNA viruses that cause serious crop losses worldwide. Begomoviruses, which constitute the largest geminivirus genus, are exclusively transmitted by the whitefly Bemisia tabaci cryptic species complex in a persistent-circulative manner. They are generally believed to be unable to replicate in their insect vectors, with the tomato yellow leaf curl virus (TYLCV) as a notable exception. The possible replication of TYLCV in the whitefly vector has captured considerable attention since 1994. There has been disagreement as to whether TYLCV can replicate in the insect vector. Thus, there needs to be compelling evidence concerning whether and how TYLCV replicates within its insect vector.

Recently, the research team led by Prof. WANG Xiaowei from the Zhejiang University Institute of Insect Sciences published an article titled “A plant DNA virus replicates in the salivary glands of its insect vector via recruitment of host DNA synthesis machinery” in the PNAS.

This research offers solid evidence and provides new insight in terms of the replication of TYLCV in the whitefly vector, primarily in salivary glands. It confirms that TYLCV induces DNA synthesis machinery, proliferating cell nuclear antigens (PCNA) and DNA polymerase δ (Polδ), to establish a replication-competent environment in whiteflies. TYLCV replication-associated protein (Rep) interacts with whitefly PCNA, which recruits DNA Polδ for virus replication. In contrast, another geminivirus, the papaya leaf curl China virus (PaLCuCNV), does not replicate in the whitefly vector. PaLCuCNV does not induce DNA-synthesis machinery, and the Rep does not interact with whitefly PCNA.

These findings reveal crucial mechanisms by which a plant DNA virus replicates across the kingdom barrier in an insect and may help to explain the global spread of this devastating pathogen.