Viral Systemic Movement Is Enhanced by Alteration of a Structural Phloem Protein by the Insect Vector.

The ability to access and exploit the vascular system is essential for viral systemic spread within plant hosts. Insect-borne viruses can be released from the vector's stylets into plant phloem together with saliva components that facilitate viral systemic spread. This study found that Myzus persicae released abundant salivary protein glucose dehydrogenase (GLD) into the phloem, establishing an oxidizing environment during feeding, which oxidized cysteine residues in the C-terminal motif of sieve element occlusion (SEO) proteins. This modification promotes SEO aggregation and directly facilitates interactions between aggregated SEOs and the coat protein of cucumber mosaic virus (CMV), thereby facilitating virus systemic movement in the phloem. When the four cysteine residues of SEO are replaced by serines, aphid GLD can no longer initiate SEO aggregation or accelerate virus systemic infection. These findings reveal a novel function of aphid GLD in accelerating systemic movement of CMV in the plant via oxidizing plant SEO proteins. This biochemical cascade allows viruses to exploit the host vascular system for systemic movement. This work identifies a crucial target in the phloem for mitigating virus infection efficiency after aphid inoculation.