DTH1-dependent remodeling of the lipid and protein environment of lipid droplets during nutrient recovery in Chlamydomonas

This is the authors' abstract. We don't add key points for this paper.

Lipid droplets (LDs) play a central role in cellular carbon and energy homeostasis, in particular through the roles played by numerous LD-associated proteins. A long-standing question concerns how these proteins are molecularly organized at the seemingly overcrowded LD surface. Delayed in TAG Hydrolysis 1 (DTH1) has been identified as a key protein for efficient LD degradation in Chlamydomonas reinhardtii , however the underlying molecular mechanism remains unknown. DTH1 contains several structural features – including a coiled-coil domain, a phosphatidylethanolamine (PE) specific lipid-binding domain, intrinsically disordered regions, and an α-helical C-terminal domain, that make it a compelling candidate for acting as a molecular scaffold in protein recruitment and/or organelle tethering. In this study, we used the Chlamydomonas knock-out mutant dth1 as an entry point to begin dissecting the molecular organization of proteins at the LD surface. Comparative lipidomic and proteomic analyses of isolated LDs from both WT and dth1 mutants revealed several key features associated with LD degradation during nutrient recovery. First, PE emerged as an important lipid species involved in LD degradation. Second, active communication occurs among multiple subcellular organelles particularly between LDs, peroxisomes and mitochondria. Third, DTH1 was found to play a critical role in remodeling both the LD proteome and lipidome. Furthermore, detailed analyses of LD degradation during nitrogen recovery uncovered the formation of micro-LDs, a phenomenon not yet reported in microalgae. Collectively, these results highlight the tight coordination of metabolic activities across subcellular compartments and emphasize the importance of intracellular carbon trafficking during stress recovery. Significance statement Lipid droplets are central hubs of cellular carbon storage and mobilization, yet how their protein and lipid composition is organized during turnover remains poorly understood. Using Chlamydomonas reinhardtii , we show that DTH1-dependent remodeling of the lipid droplet proteome and lipidome is associated with coordinated carbon mobilization involving peroxisomes and mitochondria, and identify micro-LD formation as a previously unreported feature of nutrient recovery.