PNNL

Abstract

Drought is the leading cause of agricultural crop productivity loss among all biotic and abiotic stresses, and the link between water deficiency and phloem protein contents is relatively unexplored. Here we employed the EDTA-facilitated phloem exudate collection method from Solanum lycopersicum leaves during a period of drought stress and recovery. Our analysis identified 2,558 proteins, the most abundant of which were previously localized to the phloem. Independent of drought, enrichment analysis of the total phloem exudate protein profiles from all samples suggest that the exchange of proteins into the phloem is complex, and includes proteins that function in chaperone systems, branched-chain amino acid synthesis, trehalose metabolism, and RNA silencing. During the experiment we observed 169 proteins whose abundance changed significantly within the phloem sap. Proteins that became more significantly more abundant include members of lipid metabolism, chaperone-mediated protein folding, carboxylic acid metabolism, abscisic acid signaling, cytokinin biosynthesis, and amino acid metabolism. Conversely, proteins involved in lipid signaling, sphingolipid metabolism, cell wall organization, carbohydrate metabolism, and a mitogen-activated protein kinase are downregulated in response to drought. Many of these observations support previous literature findings but have not been localized to the tomato vasculature, suggesting phloem is critical for adaptation to drought stress.