Abstract
Lettuce infectious yellows virus is the first crinivirus for which the retention of purified virions ingested into the whitefly (Bemisia tabaci New World (NW)) vector’s foregut, has been demonstrated to be a requisite for successful virus transmission. This key finding supports the hypothesis that the determinant of foregut retention and transmission is present on the virion itself. However, whether this is also true for other criniviruses has not been established. Here, we provide evidence that lettuce chlorosis virus (LCV) acquired from plants is retained in the foreguts of both the B. tabaci NW and Middle East–Asia Minor 1 (MEAM1) vector species and transmitted upon inoculation feeding. An association between foregut retention and transmission by NW vectors is also observed following the acquisition and inoculation feeding of LCV virions purified using a standard procedure involving 2% or 4% (v/v) Triton™ X-100 (TX-100). However, while virions purified with 2% or 4% TX-100 are also retained in the foreguts of MEAM1 vectors, transmission is observed with the 4% TX-100-purified virions or when more vectors are used for acquisition and inoculation feeding. These results suggest that an intrinsic difference exists between NW and MEAM1 vectors in their interactions with, and transmission of, LCV virions.
Highlights
Successful insect vector transmission of plant viruses requires a confluence of direct and indirect contributions from an insect, virus, and a plant [1,2,3]
In Planta Acquired GH-lettuce chlorosis virus (LCV) Is Retained in the Foreguts of B. tabaci New World (NW) and Middle East–Asia Minor 1 (MEAM1)
NW and MEAM1 vectors that were randomly sampled from the infected source plants both transmitted the virus to target lettuce plants, with two out of four and three out of six target plants developing infection, respectively, after they were exposed for an overnight inoculation access period (IAP) to each vector species (Table 1)
Summary
Successful insect vector transmission of plant viruses requires a confluence of direct and indirect contributions from an insect, virus, and a plant [1,2,3]. For emerging viruses in the genus Crinivirus (family Closteroviridae) [4], complexity is exemplified by their relatively large genome sizes and complicated biology associated with, but not limited to, phloem tropism and low titer infections. RNA 2 contains between 7 and 10 ORFs (depending on the crinivirus), the most conspicuous of which are those that make up the hallmark gene array of viruses in the family Closteroviridae: encoding for a hydrophobic protein, a heat shock protein 70 homolog (Hsp h), a 50–60 kDa protein (depending on the virus), a major coat protein (CP), and a minor coat protein (CPm) [6,7]. Proteins encoded by the ORFs on RNA 2 are associated with, or have been implicated in, different processes in the viral infection cycle, including virion assembly, long-distance movement, suppression of RNA silencing, and vector transmission [8,9,10,11,12,13]
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