Immunological detection of glassy-winged sharpshooter saliva in grapevines

Glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is a major vector for transmission of Xylella fastidiosa (Xf) , the causative agent of Pierce’s Disease in grapevine. During the feeding process of stylet penetration and xylem fluid ingestion, GWSS inject saliva into the plant. Inoculation and initial establishment of Xf may be aided by the presence of GWSS saliva. To better understand movement of GWSS saliva at the grapevine feeding site, an antibody to detect a dominant protein from GWSS salivary glands was developed. Beta 1,4-glucanase was isolated from GWSS salivary glands, and antibodies raised in guinea pigs. The resulting antiserum was applied to sectioned petioles from grapevines from which GWSS had fed for a limited period of time, allowing for penetration of GWSS stylets and establishment of an ingestion site in xylem cells. GWSS sheath saliva is strongly auto-fluorescent when viewed by confocal microscopy; however watery saliva does not emit auto-fluorescence. Watery saliva was visualized using anti-glucanase primary antibody and Alexa Fluor 647-conjugated goat anti-guinea pig IgG secondary antibody for confocal microscopy. Watery saliva was detected in close relation to sheath saliva and also associated with xylem and parenchyma cells along the sheath path. Movement of watery saliva through the plant matrix may assist in early establishment of Xf cells through cell wall degradation, facilitating systemic infection by Xf.