Hello darkness, my old friend: 3-Ketoacyl-Coenzyme A Synthase4 is a branch point in the regulation of triacylglycerol synthesis inArabidopsis thaliana

Abstract

Due to their sessile lifestyle, plants have evolved unique mechanisms to deal with environmental challenges. Under stress, plant lipids are important as alternative sources of carbon and energy when sugars or starch are limited. Here, we applied combined heat and darkness and extended darkness to a panel of ∼ 300 Arabidopsis accessions to study lipid remodeling under carbon starvation. Natural allelic variation at 3-KETOACYL-COENZYME A SYNTHASE4 (KCS4), a gene encoding for an enzyme involved fatty-acid elongation, underlies a differential accumulation of polyunsaturated triacylglycerols (TAGs) under stress. Ectopic expression in yeast and plants proved that KCS4 is a functional enzyme localized in the ER with specificity for C22 and C24 saturated acyl-CoA. Loss-of-function mutants and transient overexpression in planta revealed the role of KCS4 alleles in TAG synthesis and biomass accumulation. The region harboring KCS4 is under high selective pressure. Furthermore, allelic variation at KCS4 correlated with environmental parameters from the locales of Arabidopsis accessions. Our results provide evidence that KCS4 plays a decisive role in the subsequent fate of fatty acids released from chloroplast-membrane lipids under carbon starvation. This work sheds light on both plant response mechanisms to abiotic stress and the evolutionary events shaping the lipidome under carbon starvation.One sentence summaryNatural variation at KCS4 underlies a differential accumulation of polyunsaturated triacylglycerols, by acting as a regulatory branch point in the fate of fatty acids under carbon starvation.

Genome-wide association of the metabolic shifts underpinning dark-induced senescence in Arabidopsis

“…Membrane lipids are another alternative important C source for plant cells that are degraded to TAGs and subsequently degraded through β-oxidation to produce vital alternative respiration substrates ( Avin-Wittenberg et al, 2015 ). In this study, consistent with data presented previously ( Luzarowska et al, 2020) , we discovered a very strong association between 3-KETOACYL-COA SYNTHASE 4 ( KCS4 ) and unsaturated TAGs in the dark-related datasets, supporting the important role of KCS4 in lipid recycling upon darkness ( Supplemental Data Set S2 ). During recycling, transport of the compounds is also a crucial step for the transformation of metabolites.…”

“…In addition to these metabolites, TAGs, β-alanine, nicotinic acid, and some PCs also belonged in Cluster 5. As the loci associated with TAG 54:9, β-alanine levels as well as the involvement of the 3-hydroxyisobutyryl-CoA hydrolase CHY4 on leucine degradation have been previously reported ( Wu et al, 2016 ; Gipson et al, 2017 ; Luzarowska et al, 2020 ; Supplemental Figure S4 ; Supplemental Data Set S2 ) and corroborate the accuracy of our present analysis, we focused on two loci associated with tyrosine and threonine levels to illustrate their detailed genetic regulation.…”

“…The workflow included peak detection, retention time alignment, and removal of chemical noise. Isotopic peak detection from the MS data was performed as described in Luzarowska et al (2020) . Identified lipids were confirmed by manual verification of the chromatograms using Xcalibur (version 3.0, Thermo-Fisher, Bremen, Germany).…”

“…Despite the fact that microarray data have allowed a broad view of the transcriptional responses to dark-induced senescence, an understanding of the large scale metabolic shifts of the nutrient recycling (such as amino acids, lipids, and sugars) to guarantee plant survival, which can give some cues to biofortify crop quality and stress resistance, remains fragmentary. Indeed, most studies to date have either looked at the regulation of protein or lipid degradation independently ( Kunz et al, 2009 ; Araujo et al, 2011b ; Luzarowska et al, 2020) , while a comprehensive study to that of developmental-induced senescence has not yet been conducted ( Watanabe and Lam, 2004 ). However, fairly complete surveys of the transcriptional and metabolic changes in autophagy-deficient mutants of Arabidopsis ( Arabidopsis thaliana ) have recently been reported ( Avin-Wittenberg et al, 2015 ; Barros et al, 2017 ), with many shared metabolic features between these and the targeted studies described above.…”

Integrating multiomics data accelerates elucidation of plant primary and secondary metabolic pathways

“…In general, based on machine characteristics, an individual-specific LC-MS reference library is established by a lab, through integrating the retention times and mass spectra information for the standard components, useful mass spectra datasets (such as Lipid Maps, http://www.lipidmaps.org/index. html and ReSpect database, http://spectra.psc.riken.jp/ menta.cgi/respect/search/fragment) and information in the public domain (Luzarowska et al 2020;Wang et al 2019).…”