With these thoughts in mind, the three cysteines in the CP or RTP of CYDV-RPV may provide some clues (Fig. S2 ) as to why sodium sulfite treatment would affect the virus-plant interactome. Two of the cysteines are flanked by at least one basic amino acid. These are likely the most reactive cysteines in the CP or RTP with respect to the formation of S-sulfonates and would readily participate in thiol-disulfide exchange reactions initiated by the sulfolysis of other disulfide bonds. Blocking the critical thiol by converting it to a thiosulfonate or otherwise modifying critical interactions via the formation of a non-native disulfide could have negative consequences for the internalization of RPV into aphid cells, as is observed for a wide range of other viruses (enveloped and non-enveloped) that rely on disulfide bond formation for internalization into and transport through host cells [48, 49, 50] . In contrast to the sodium sulfite treatment, EDTA treatment did not prevent entry of virus into aphid cells or transmissibility, but it did appear to reduce the long term stability of the virus inside the aphid. Hence, in vivo interactions between divalent cations and the virus capsid may be required for long-term virion stability. Indeed, other icosahedral plant viruses such as rice yellow mottle virus, tomato bushy stunt virus, southern bean mosaic virus and cowpea chlorotic mottle virus are stabilized by divalent cations such as Ca 2+ and Mg 2+ , [40, 51, 52, 53, 54] .