Asst. Prof.; Director of BMB Undergraduate Education; Associate Director of Genetics and Genome Sciences Graduate Program Michigan State University
To survive fluctuating environmental conditions, plants must adjust their development. While there are many known local signals that respond to environmental stresses, systemic coordination via long-distance signaling mechanisms is essential for a rapid distal response. Long-distance transport in plants occurs in the vascular bundles. One component, the phloem is a dynamic tissue that not only to transports photoassimilates from source to sink but also traffics metabolites, nucleic acids, proteins, and even lipids. We identified a number of predicted lipid-binding proteins (LBPs) in the phloem and examined their lipid-binding properties, their localization, and their expression in response to environmental factors. Interestingly, lipids such as oxylipins and phosphatidic acid are found in the phloem sap as well. We propose that phloem LBPs act in long-distance, lipid-mediated signaling to systemically coordinate the plant’s response to stress. We have shown that one of these proteins, PHLOEM LIPID-ASSOCIATED FAMILY PROTEIN (PLAFP) specifically binds phosphatidic acid (PA) and that PLAFP is induced by the same abiotic stresses that induce production of PA. More importantly, changes in PLAFP expression also affect the phloem PA content. We are investigating the PLAFP-PA movement and the biochemical mechanism by which PLAFP interacts with PA in the phloem. A pull down approach revealed putative PLAFP-interacting proteins, including a receptor-like kinase, which could mediate downstream signaling. Y2H and confocal microscopy of tagged proteins were used to confirm interaction. To better understand the PLAFP-PA interaction, computational alignment and modeling of the ligand-binding sites, crystallography and site-directed mutagenesis is followed by lipid binding assays. Lipid movement is studied using radiolabeled PA. We will employ optogenetics to investigate PLAFP systemic movement and the role of PA in the mobile complex.
This project was funded in part by USDA grant #MICL04147 and NSF grants #1144391/1841251 to SHB and USDA-NIFA NNF 2015-38420-23697 to AK.
Coauthors: Amanda Koenig – Michigan State University