Arabidopsis thaliana EARLY RESPONSIVE TO DEHYDRATION 7 localizes to lipid droplets via its senescence domain

Authors: DONER, NATHAN - University Of Guelph; Seay, Damien Chris; Mehling, Marina; SUN, SIQI - University Of Gottingen; GIDDA, SATINDER - University Of Guelph; SCHMITT, KERSTIN - University Of Gottingen; BRAUS, GERHARD - University Of Gottingen; ISCHEBECK, TILL - University Of Gottingen; CHAPMAN, KENT - University Of North Texas; Dyer, John; MULLEN, ROBERT - University Of Guelph

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2021
Publication Date: 4/14/2021
Citation: Doner, N.M., Seay, D., Mehling, M.E., Sun, S., Gidda, S.K., Schmitt, K., Braus, G.H., Ischebeck, T., Chapman, K.D., Dyer, J.M., Mullen, R.T. 2021. Arabidopsis thaliana EARLY RESPONSIVE TO DEHYDRATION 7 localizes to lipid droplets via its senescence domain. Frontiers in Plant Science. 12. Article 658961. https://doi.org/10.3389/fpls.2021.658961.
DOI: https://doi.org/10.3389/fpls.2021.658961

Interpretive Summary: Plants are sessile organisms that must adapt to environmental challenges in order to survive, and knowledge of the underlying molecular mechanisms provides important insight that is useful for crop improvement using molecular breeding approaches. One of the common cellular features of plant stress response is a proliferation of subcellular organelles called “lipid droplets” (LDs), which contain neutral lipids and other lipids that are presumed to be important for stress adaptation. However, how these organelles participate in the stress adaption process is poorly understood, due in part to the limited numbers of proteins known to be associated with LDs. In a collaborative effort between scientists at the ARS lab in Maricopa, Arizona, the University of North Texas, University of Guelph, and University of Göttingen, a protein called ERD7 (EARLY RESPONSIVE TO DEHYDRATION 7) was shown to localize specifically to LDs in drought-stressed plant leaves. ERD7 is known to be strongly upregulated at the gene expression level in response to drought and other abiotic stresses, but its subcellular location was previously unknown. ERD7 was further shown to be a member of a small gene family in plants that contains two distinct types of proteins, with one group targeting to LDs, and another to mitochondria. The closest ERD7-like protein in mammals, called spartin, is known to localize to either LDs or mitochondria under various conditions. These findings describe a new gene family in plants and establish clear linkages between a known stress-response protein, ERD7, and targeting to organelles (LDs) that are known to proliferate during the stress response process. These observations open new avenues of research for further exploring the functional mechanisms of stress adaptation in plants, and will be valuable to other scientists studying plant mechanistic processes with an eye towards improving the drought and stress tolerance in crops.

Technical Abstract: Lipid droplets (LDs) are neutral-lipid-containing organelles found in all kingdoms of life and are coated with proteins that carry out a vast array of functions. Compared to mammals and yeast, relatively few LD proteins have been identified in plants, particularly those associated with LDs in vegetative (non-seed) cell types. Thus, to better understand the cellular roles of LDs in plants, a more comprehensive inventory and characterization of LD proteins is required. Here we performed a proteomics analysis of LDs isolated from drought-stressed Arabidopsis leaves and identified EARLY RESPONSIVE TO DEHYDRATION 7 (ERD7) as a putative LD protein. mCherry-tagged ERD7 localized to both LDs and the cytosol when ectopically expressed in plant cells, and the protein’s C-terminal senescence domain (SD) was both necessary and sufficient for LD targeting. Phylogenetic analysis revealed that ERD7 belongs to a six-member family in Arabidopsis that, along with homologs in other plant species, is separated into two distinct clades. Notably, the SDs of proteins from each clade conferred targeting to either LDs or mitochondria. Further, the SD from the ERD7 homolog in humans, spartin, localized to LDs in plant cells, similar to its localization in mammals; although, in mammalian cells, spartin also conditionally localizes to other subcellular compartments, including mitochondria. Disruption of ERD7 gene expression in Arabidopsis revealed no obvious changes in LD numbers or morphology, suggesting the protein is not essential for maintaining plant LD homeostasis. However, a yeast two-hybrid screen using ERD7 as bait identified numerous proteins involved in stress response. Collectively, these observations provide new insight to ERD7 and the SD-containing family of proteins in plants and suggest that ERD7 is involved in functional aspects of plant stress response that also include localization to the LD surface.