Arabidopsis lipid droplet‐associated protein (LDAP) – interacting protein (LDIP) influences lipid droplet size and neutral lipid homeostasis in both leaves and seeds

Abstract

Cytoplasmic lipid droplets (LDs) are found in all types of plant cells; they are derived from the endoplasmic reticulum and function as a repository for neutral lipids, as well as serving in lipid remodelling and signalling. However, the mechanisms underlying the formation, steady-state maintenance and turnover of plant LDs, particularly in non-seed tissues, are relatively unknown. Previously, we showed that the LD-associated proteins (LDAPs) are a family of plant-specific, LD surface-associated coat proteins that are required for proper biogenesis of LDs and neutral lipid homeostasis in vegetative tissues. Here, we screened a yeast two-hybrid library using the Arabidopsis LDAP3 isoform as 'bait' in an effort to identify other novel LD protein constituents. One of the candidate LDAP3-interacting proteins was Arabidopsis At5g16550, which is a plant-specific protein of unknown function that we termed LDIP (LDAP-interacting protein). Using a combination of biochemical and cellular approaches, we show that LDIP targets specifically to the LD surface, contains a discrete amphipathic α-helical targeting sequence, and participates in both homotypic and heterotypic associations with itself and LDAP3, respectively. Analysis of LDIP T-DNA knockdown and knockout mutants showed a decrease in LD abundance and an increase in variability of LD size in leaves, with concomitant increases in total neutral lipid content. Similar phenotypes were observed in plant seeds, which showed enlarged LDs and increases in total amounts of seed oil. Collectively, these data identify LDIP as a new player in LD biology that modulates both LD size and cellular neutral lipid homeostasis in both leaves and seeds.

PUX10 Is a CDC48A Adaptor Protein That Regulates the Extraction of Ubiquitinated Oleosins from Seed Lipid Droplets in Arabidopsis

“…The molecular machinery by which PUX10 is translocated to LDs is currently unknown. However, the translocation mechanism is probably distinct from the ARF1/COPI-mediated mechanism described in mammals (Wilfling et al, 2014), since proteins of the ARF family were not identified in the LD proteome of Arabidopsis seedlings (Pyc et al, 2017b). Unexpectedly, we observed a dramatic change of PUX10 localization during the transition between embryogenesis and seed maturation.…”

PUX10 Is a Lipid Droplet-Localized Scaffold Protein That Interacts with CELL DIVISION CYCLE48 and Is Involved in the Degradation of Lipid Droplet Proteins

“…These proteins, first discovered on LDs of avocado (Persea americana) mesocarp (Horn et al, 2013), are also present in Arabidopsis thaliana, where they are needed for the proper compartmentation of neutral lipids during postgerminative seedling growth and also in mature leaves, especially under drought stress conditions (Gidda et al, 2016;Kim et al, 2016). A similar role has been proposed for the LDAP interaction partner LDIP (LDAP-interacting protein; Pyc et al, 2017b).…”

Nonspecific phospholipase C6 increases seed oil production in oilseed Brassicaceae plants

“…Specific genes involved in lipid biosynthesis (Zhang et al , 2009; Aznar‐Moreno & Durrett, 2017), hydrolysis (Eastmond, 2006; Kelly et al , 2011) and transport (S. Kim et al , 2013; N. Li et al , 2015), as well as in glycolysis and transcriptional regulation (Cernac & Benning, 2004; Mu et al , 2008; Santos‐Mendoza et al , 2008; Kim et al , 2019), have been shown to influence seed oil accumulation. In addition, proteins involved in lipid droplet formation also affect lipid accumulation (Cai et al , 2015; Pyc et al , 2017). The polygenic and quantitative trait loci contributing to seed oil and yield result from accumulated minor effects from hundreds or thousands of years of crop selection and domestication of the target traits.…”