Reason for non-aphid transmissibility in a strain of Kalanchoë mosaic potyvirus

Kalanchoë mosaic potyvirus (KMV) is transmitted by aphids in a nonpersistent manner. After multiple mechanical inoculations, a non-aphid-transmissible (NAT) variant appeared. Addition of purified helper component (HC) from potato virus Y-infected plants did not restore the aphid transmissibility of purified KMV-NAT. Comparison of the nucleotide sequence in the N-terminal half of the coat protein gene of KMV-NAT with that of an aphid-transmissible (AT) KMV strain revealed a single nucleotide difference (G to A). This nucleotide change turns a glycine residue (G) in the KMV-AT isolate into a glutamic acid residue (E) in the KMV-NAT isolate, abolishing the Asp-Ala-Gly (DAG) sequence, which has previously been shown to be essential for aphid transmission. The experiments show that non-aphid transmissibility is most likely caused by the change in the DAG sequence.