Lipid remodeling regulator 1 (LRL1) is differently involved in the phosphorus‐depletion response from PSR1 in Chlamydomonas reinhardtii

Abstract

Summary The elucidation of lipid metabolism in microalgae has attracted broad interest, as their storage lipid, triacylglycerol (TAG), can be readily converted into biofuel via transesterification. TAG accumulates in the form of oil droplets, especially when cells undergo nutrient deprivation, such as for nitrogen (N), phosphorus (P), or sulfur (S). TAG biosynthesis under N‐deprivation has been comprehensively studied in the model microalga Chlamydomonas reinhardtii, during which TAG accumulates dramatically. However, the resulting rapid breakdown of chlorophyll restricts overall oil yield productivity and causes cessation of cell growth. In contrast, P‐deprivation results in oil accumulation without disrupting chloroplast integrity. We used a reverse genetics approach based on co‐expression analysis to identify a transcription factor (TF) that is upregulated under P‐depleted conditions. Transcriptomic analysis revealed that the mutants showed repression of genes typically associated with lipid remodeling under P‐depleted conditions, such as sulfoquinovosyl diacylglycerol 2 (SQD2), diacylglycerol acyltransferase (DGTT1), and major lipid droplet protein (MLDP). As accumulation of sulfoquinovosyl diacylglycerol and TAG were suppressed in P‐depleted mutants, we designated the protein as lipid remodeling regulator 1 (LRL1). LRL1 mutants showed slower growth under P‐depletion. Moreover, cell size in the mutant was significantly reduced, and TAG and starch accumulation per cell were decreased. Transcriptomic analysis also suggested the repression of several genes typically upregulated in adaptation to P‐depletion that are associated with the cell cycle and P and lipid metabolism. Thus, our analysis of LRL1 provides insights into P‐allocation and lipid remodeling under P‐depleted conditions in C. reinhardtii. Open Research Badges This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The sequencing data were made publicly available under the BioProject Accession number PRJDB6733 and an accession number LC488724 at the DNA Data Bank of Japan (DDBJ). The data is available at https://trace.ddbj.nig.ac.jp/BPSearch/bioproject?acc=PRJDB6733; http://getentry.ddbj.nig.ac.jp/getentry/na/LC488724. The metabolome data were made publicly available and can be accessed at http://metabolonote.kazusa.or.jp/SE195:/; http://webs2.kazusa.or.jp/data/nur/.

Stresses as First-Line Tools for Enhancing Lipid and Carotenoid Production in Microalgae

“…When PSR1 was overexpressed in C. reinhardtii , TAG accumulation was increased ( Ngan et al, 2015 ). Recently, the transcription factor lipid remodeling regulator 1 (LRL1) was found in C. reinhardtii by transcriptomic analysis, which is a regulator of both membrane remodeling and TAG biosynthesis under phosphorus-limitation ( Hidayati et al, 2019 ). In the future, LRL1 could be a potential target of engineering for improving lipid accumulation in microalgae.…”

Fixing the Broken Phosphorus Cycle: Wastewater Remediation by Microalgal Polyphosphates

“…This is probably an indication that rates of fatty acid synthesis under nutrient-replete conditions are adequate to support the level of TAG synthesis seen with nutrient-stress in this species; either with or without the sta6 mutation, which prevents starch synthesis and boosts flux to TAG ( Blaby et al, 2013 ). A further MYB TF gene, LRL1 appears to be influential for maximizing some of the late-response P-deprivation responses ( Figure 6 ) ( Hidayati et al, 2019 ).…”

CO2 supply modulates lipid remodelling, photosynthetic and respiratory activities in Chlorella species

“…Phospholipids were reduced whereas the betaine lipid DGTS were increased in both species by high CO 2 level. Betaine lipid, a non-phospholipid, has been observed often increased during phosphate limitation, presumably replacing the function of phospholipids in cell membranes (Riekhof et al, 2014; Murakami et al, 2018; Hidayati et al, 2019). For still unknown reasons, a similar response between P limitation and high CO 2 was observed.…”