Analysis of Xylem Tissue and Xylem Sap Proteome Reveal Disease Tolerance Mechanisms Among Grape Species

Pierce’s disease (PD), caused by bacterium Xylella fastidiosa, seriously hampers the cultivation of grape. The bacterium is transmitted by the xylem sap-feeding sharpshooter, which clogs xylem vessels causing the plant to wilt. Most vinifera are susceptible to PD, and exhibit genetic diversity for the disease responses. Muscadine grapes are known to be tolerant to most diseases, while Florida hybrid bunch (FH) cultivars exhibit PD tolerance. Plants respond to infection by up-regulating the expression or by inducing some unique proteins for protection against pathogens. Hence, the comparative proteome analysis of xylem tissue and xylem sap of vinifera, muscadine (Vitis rotundifolia), and FH was carried out for better understanding the metabolic pathways involved in tolerance mechanisms. We used LC MS/MS approach and identified 1,971 and 377 proteins from xylem tissue and xylem sap respectively. Further functional analysis revealed that Muscadine and FH possesses 9 unique proteins in xylem tissue, and 48 in xylem sap, which are absent in vinifera. These proteins are involved in contributing to the plant defense against bacterium and also for oxygen generation. Novel proteins, such as receptor-like protein kinase feronia-like, peroxidase, glucan endo-1, 3-beta-glucosidase 4-like proteins are involved in metabolic process, defense response, and peroxidase activity.  Among the differentially expressed proteins, stress and defense activity related proteins are more abundant in Florida hybrid bunch and muscadine xylem and xylem sap when compared to their levels in V. vinifera tissue and sap.