Cucumber mosaic virus 2b proteins inhibit virus‐induced aphid resistance in tobacco

Abstract

Cucumber mosaic virus (CMV), which is vectored by aphids, has a tripartite RNA genome encoding five proteins. In tobacco (Nicotiana tabacum), a subgroup IA CMV strain, Fny-CMV, increases plant susceptibility to aphid infestation but a viral mutant unable to express the 2b protein (Fny-CMV∆2b) induces aphid resistance. We hypothesized that in tobacco, one or more of the four other Fny-CMV gene products (the 1a or 2a replication proteins, the movement protein, or the coat protein) are potential aphid resistance elicitors, whilst the 2b protein counteracts induction of aphid resistance. Mutation of the Fny-CMV 2b protein indicated that inhibition of virusinduced resistance to aphids (Myzus persicae) depends on amino acid sequences known to control nucleus-to-cytoplasm shuttling. LS-CMV (subgroup II) also increased susceptibility to aphid infestation but the LS-CMV∆2b mutant did not induce aphid resistance. Using reassortant viruses comprising different combinations of LS and Fny genomic RNAs, we showed that Fny-CMV RNA 1 but not LS-CMV RNA 1 conditions aphid resistance in tobacco, suggesting that the Fny-CMV 1a protein triggers resistance. However, the 2b proteins of both strains suppress aphid resistance, suggesting that the ability of 2b proteins to inhibit aphid resistance is conserved among divergent CMV strains.

Manipulation of Jasmonate Signaling by Plant Viruses and Their Insect Vectors

“…Plant viral diseases are one of the most important pathogens causing agricultural losses. Currently, the emergence and reemergence of insect-transmitted plant viruses in the past decades have been mainly driven by planthoppers, whiteflies, aphids and thrips [116][117][118][119][120]. We and many other groups in the world have developed several biotechnological methods to improve crop resistance against these vector-borne viruses with the expression of virus-targeting RNA interference [121][122][123].…”

Effects of the cucumber mosaic virus 2a protein on aphid–plant interactions in Arabidopsis thaliana

“…Infectious RNA mixtures for these reassortant and recombinant viruses were used to inoculate Nicotiana benthamiana plants for preparation of virions to use as inocula for experiments with A. thaliana (Palukaitis, 2019). We recently used a similar approach with Fny-CMV/LS-CMV reassortants to successfully identify the viral RNA conditioning antibiosis (strong resistance) against aphids in Nicotiana tabacum (Tungadi et al, 2020). RNA was isolated from systemically infected leaves, subjected to reverse transcription-PCR (RT-PCR) to amplify RNA 2-specific sequences and these amplicons sequenced to confirm that all recombinant RNA 2 molecules were genetically stable and did not undergo further mutation during replication and movement through the plant.…”

“…The recombinant RNA 2 used to constitute this reassortant virus possesses the ORF for the Fny-CMV 2b protein (Figure 1b). The Fny-CMV 2b protein can induce a variety of effects on performance of aphids on tobacco plants infected with Fny-CMV (Ziebell et al, 2011;Tungadi et al, 2020) and in 2b-transgenic A. thaliana plants (Westwood et al, 2013). However, because infection with F1-L 1-300 F-F3 did not induce F I G U R E 1 Design of recombinant CMV RNA 2 molecules to identify CMV 2a protein sequences that influence plant-aphid interactions.…”

“…One-day-old aphid nymphs (10-12 aphids per treatment per experiment) were weighed using a microbalance, placed on plants, reweighed 5 days later, and the mean relative growth rate (MRGR) calculated as previously described (Leather and Dixon, 1984;Stewart et al, 2009;Ziebell et al, 2011;Westwood et al, 2013) (histograms on left). Ten days later the offspring produced by each aphid were counted and the mean colony size calculated (Ziebell et al, 2011;Westwood et al, 2013;Tungadi et al, 2020) (histograms on right). Plants were mock-inoculated (Mock) with sterile water or inoculated with purified virions of reconstituted Fny-CMV (F1-F2-F3), the reassortant Fny-CMV/LS-CMV virus F1-L2-F3, or viruses possessing RNAs F1, F3, and one of the indicated Fny-CMV(F)/ LS-CMV(L) recombinant RNA 2 molecules (described in Figure 1b).…”

Molecular Insights into Host and Vector Manipulation by Plant Viruses

“…However, tobacco plants infected with CMV∆2b showed a dramatic reduction in aphid populations, indicating that the 2b protein was able to repress resistance to aphid infestation in tobacco. By using viral reassortants created by shuffling the genomic RNAs from Fny-CMV and LS-CMV strains, Tungadi et al [34] showed that in tobacco, Fny-CMV but not LS-CMV RNA 1 (or its 1a protein, a replication-associated factor) triggers resistance to aphids, while the 2b protein of both strains suppressed aphid resistance. In contrast, in arabidopsis aphid antibiosis is induced by Fny-CMV 2b protein and 1a prevents 2b's effect [35].…”