Rapid accumulation and low degradation: key parameters of Tomato yellow leaf curl virus persistence in its insect vector Bemisia tabaci

Abstract

Of worldwide economic importance, Tomato yellow leaf curl virus (TYLCV, Begomovirus) is responsible for one of the most devastating plant diseases in warm and temperate regions. The DNA begomoviruses (Geminiviridae) are transmitted by the whitefly species complex Bemisia tabaci. Although geminiviruses have long been described as circulative non-propagative viruses, observations such as long persistence of TYLCV in B. tabaci raised the question of their possible replication in the vector. We monitored two major TYLCV strains, Mild (Mld) and Israel (IL), in the invasive B. tabaci Middle East-Asia Minor 1 cryptic species, during and after the viral acquisition, within two timeframes (0–144 hours or 0–20 days). TYLCV DNA was quantified using real-time PCR, and the complementary DNA strand of TYLCV involved in viral replication was specifically quantified using anchored real-time PCR. The DNA of both TYLCV strains accumulated exponentially during acquisition but remained stable after viral acquisition had stopped. Neither replication nor vertical transmission were observed. In conclusion, our quantification of the viral loads and complementary strands of both Mld and IL strains of TYLCV in B. tabaci point to an efficient accumulation and preservation mechanism, rather than to a dynamic equilibrium between replication and degradation.

Vector development and vitellogenin determine the transovarial transmission of begomoviruses

“…However, whether begomoviruses can be transmitted transovarially is still in great controversy. Although most of the studies reported absence of transovarial transmission (35)(36)(37)(38)(39), several studies reported the presence of transovarial transmission, but the efficiencies varied considerably between studies (40-42) (Table S1). Our study proved that TYLCV can be effectively transmitted via ovary of whitefly adults of elder age, but not by whitefly adults of very young age (Fig.…”

Tomato yellow leaf curl virus: No evidence for replication in the insect vector Bemisia tabaci

“…TYLCV purified virions were acquired by whiteflies on an artificial sucrose diet in an attempt to provide them only encapsidated virus VS forms. Thus, acquisition from plants as done in previous studies 10 15 17 was not performed to diminish or prevent the acquisition of CS forms and/or viral transcription and/or replication complexes that could be present in infected plants. Also, previous to virus acquisition, purified virions were treated with DNase I to eliminate or reduce the presence of non-encapsidated viral nucleic acids.…”

“…Also, previous to virus acquisition, purified virions were treated with DNase I to eliminate or reduce the presence of non-encapsidated viral nucleic acids. Moreover, after AAP and until analysis, whiteflies were maintained on an artificial diet and not on a virus non-host plants as done in previous studies 16 17 to eliminate plant factors that could help to complete the virus life cycle within the whiteflies. The infectivity of purified-DNase I-treated virions was confirmed through B. tabaci transmission to tomato plants.…”

“…Thus, results obtained by Pakkianathan et al 16 seem to support replication of an Israeli isolate of TYLCV (a strain not specified but presumably belonging to the strain Israel, IL) within the insect vector. In contrast, no such replication was observed by Becker et al 17 for isolates of the Mild (TYLC-Mld) and IL (TYLCV-IL) strains of TYLCV.…”

“…In the present study we contribute to the debate on whether TYLCV can replicate in B. tabaci by providing data from direct quantitative analysis of viral CS and VS DNA strands accumulation within B. tabaci individuals using a recently developed sensitive and strand-specific amplification procedure 18 . Analyses conducted by Pakkianathan et al 16 and Becker et al 17 were performed on B. tabaci individuals maintained on TYLCV non-host plants until they were analyzed after the virus acquisition access period (AAP). Here, we assess the ability of TYLCV to replicate in the insect in the absence of plant factors that could complement virus replication by feeding the whiteflies on preparations of purified virions during the virus AAP and maintaining them on an artificial diet after the AAP.…”