Abstract
During moderate drought stress, plants can adjust by changes in the protein profiles of the different organs. Plants transport and modulate extracellular stimuli local and systemically through commonly induced inter- and intracellular reactions. However, most proteins are frequently considered, cell and organelle specific. Hence, while signaling molecules and peptides can travel systemically throughout the whole plant, it is not clear, whether protein isoforms may exist ubiquitously across organs, and what function those may have during drought regulation. By applying shotgun proteomics, we extracted a core proteome of 92 identical protein isoforms, shared ubiquitously amongst several Medicago truncatula tissues, including roots, phloem sap, petioles, and leaves. We investigated their relative distribution across the different tissues and their response to moderate drought stress. In addition, we functionally compared this plant core stress responsive proteome with the organ-specific proteomes. Our study revealed plant ubiquitous protein isoforms, mainly related to redox homeostasis and signaling and involved in protein interaction networks across the whole plant. Furthermore, about 90% of these identified core protein isoforms were significantly involved in drought stress response, indicating a crucial role of the core stress responsive proteome (CSRP) in the plant organ cross-communication, important for a long-distance stress-responsive network. Besides, the data allowed for a comprehensive characterization of the phloem proteome, revealing new insights into its function. For instance, CSRP protein levels involved in stress and redox are relatively more abundant in the phloem compared to the other tissues already under control conditions. This suggests a major role of the phloem in stress protection and antioxidant activity enabling the plants metabolic maintenance and rapid response upon moderate stress. We anticipate our study to be a starting point for future investigations of the role of the core plant proteome. Under an evolutionary perspective, CSRP would enable communication of different cells with each other and the environment being crucial for coordinated stress response of multicellular organisms.
Highlights
Understanding the context in which long-distance signaling function, whole-plant organ and multicellular level processes must be investigated (Lough and Lucas, 2006)
Hahn and colleagues investigated gene expression profiles of Arabidopsis thaliana roots and leaves in response to various abiotic stresses and classified the plant core environmental stress response (PCESR) genes into three different categories: (1) genes regulated in the stressed tissue only, (2) Genes regulated in non-treated tissue only, and (3) Genes regulated in roots and leaves
During the water deficit study, control (C) plants were irrigated with water to avoid nutritional differences, while the water deficit stressed plants were irrigated with 50% of the evapotranspired water every 2 days to induce a progressive and moderate water deficit stress (MD) after 7 days when the leaf water potential ( w) reached the value w = −1.50 ± 0.02 MPa
Summary
Understanding the context in which long-distance signaling function, whole-plant organ and multicellular level processes must be investigated (Lough and Lucas, 2006). The phloem macromolecular translocation system contains small molecules such as phytohormones, small RNA, mRNA and proteins (Lucas et al, 2001; Aoki et al, 2005; Kehr and Buhtz, 2008; Guelette et al, 2012). Those studies disclosed interactions of several proteins or RNA and proteins to facilitate or regulate translocation through the phloem. Their study on phloem proteins from pumpkin (Cucurbita maxima) revealed that while the shoot-ward movement was carried passively by bulk flow, while protein-protein interaction (through specific phloem proteins, including eukaryotic initiation factor 5A, and a translationally controlled tumor protein) regulated the selective translocation of RNA binding proteins root-ward
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