Vascular Sap Proteomics: Providing Insight into Long-Distance Signaling during Stress

Abstract

The plant vascular system, composed of the xylem and phloem, is important for the transport of water, mineral nutrients, and photosynthate throughout the plant body. The vasculature is also the primary means by which developmental and stress signals move from one organ to another. Due to practical and technological limitations, proteomics analysis of xylem and phloem sap has been understudied in comparison to accessible sample types such as leaves and roots. However, recent advances in sample collection techniques and mass spectrometry technology are making it possible to comprehensively analyze vascular sap proteomes. In this mini-review, we discuss the emerging field of vascular sap proteomics, with a focus on recent comparative studies to identify vascular proteins that may play roles in long-distance signaling and other processes during stress responses in plants.

Effects of Fe and Mn deficiencies on the protein profiles of tomato ( Solanum lycopersicum ) xylem sap as revealed by shotgun analyses

“…The exact role that this lipase plays in the Fe deficiency response is not clear. However, the presence of four more proteins related to lipid metabolism (two increasing and two decreasing), and especially the 3-fold increase of a lipid transfer protein (K4BFV4) could support the existence of a lipid-based signaling system in the xylem sap [2]. Interestingly, upon Mn shortage, significant decreases were measured in all six proteins related to lipid metabolism, including a GDSL motif lipase and two lipid transfer proteins.…”

“…A C C E P T E D M A N U S C R I P T tomato (see [7] for a review). A comprehensive analysis of these proteomes, which included between 100 and 500 proteins, indicated that the major functional category in the xylem is polysaccharide metabolism, including mainly cell wall hydrolases [2,7,12]. The xylem proteome, as it also occurs in other plant fluids, contains a battery of proteins related to redox homeostasis, plant defense and proteases, which are thought to constitute a local defense barrier against biotic and abiotic stresses [7,[16][17][18][19].…”

“…Interestingly, the xylem sap proteome also contains a small number of proteins involved in regulatory processes that could participate in root to shoot signaling, including transcription factors, fasciclin-like arabinogalactan proteins and kinases [2,7,[29][30][31].…”

Citrus vascular proteomics highlights the role of peroxidases and serine proteases during Huanglongbing disease progression

“…Homologs of citrus proteins identified by mass spectrometry were identified using BLAST analyses (version 2.2.18) against Arabidopsis thaliana (49,50) and Cucumis sativus (51) phloem proteins with an E-value of 1e−10 required for protein identification. The Venn diagram was generated using the vennueler R package (52).…”

“…Therefore, we centrifuged the outer bark to extract vascular exudates and enrich for phloem proteins. We compared the overlap in protein identifications between our study with studies performed in Cucumis sativus and Arabidopsis (49)(50)(51). Citrus homologs for 62% and 64% of the Arabidopsis and Cucumis sativus proteins were identified, respectively (Fig.…”