Discovery and Characterization of the 3-Hydroxyacyl-ACP Dehydratase Component of the Plant Mitochondrial Fatty Acid Synthase System

Abstract

We report the characterization of the Arabidopsis (Arabidopsis thaliana) 3-hydroxyacyl-acyl carrier protein dehydratase (mtHD) component of the mitochondrial fatty acid synthase (mtFAS) system, encoded by AT5G60335. The mitochondrial localization and catalytic capability of mtHD were demonstrated with a green fluorescent protein transgenesis experiment and by in vivo complementation and in vitro enzymatic assays. RNA interference (RNAi) knockdown lines with reduced mtHD expression exhibit traits typically associated with mtFAS mutants, namely a miniaturized morphological appearance, reduced lipoylation of lipoylated proteins, and altered metabolomes consistent with the reduced catalytic activity of lipoylated enzymes. These alterations are reversed when mthd-rnai mutant plants are grown in a 1% CO 2 atmosphere, indicating the link between mtFAS and photorespiratory deficiency due to the reduced lipoylation of glycine decarboxylase. In vivo biochemical feeding experiments illustrate that sucrose and glycolate are the metabolic modulators that mediate the alterations in morphology and lipid accumulation. In addition, both mthd-rnai and mtkas mutants exhibit reduced accumulation of 3-hydroxytetradecanoic acid (i.e. a hallmark of lipid A-like molecules) and abnormal chloroplastic starch granules; these changes are not reversible by the 1% CO 2 atmosphere, demonstrating two novel mtFAS functions that are independent of photorespiration. Finally, RNA sequencing analysis revealed that mthd-rnai and mtkas mutants are nearly equivalent to each other in altering the transcriptome, and these analyses further identified genes whose expression is affected by a functional mtFAS system but independent of photorespiratory deficiency. These data demonstrate the nonredundant nature of the mtFAS system, which contributes unique lipid components needed to support plant cell structure and metabolism.

Regulation of fatty acid and flavonoid biosynthesis by miRNAs in Lonicera japonica

“…[27][28][29] ACP is involved in the pathway for fatty acid synthesis and export. 30,31 FAH could catalyse the synthesis of hydroxylated fatty acid moieties, absence of which could increase the salicylate levels and resistance towards obligate biotrophic fungal pathogens. 32 In contrast, the expression levels of U3938865 and U4351355 were higher in FLJ compared to those in rFLJ.…”

Identification and Phenotypic Characterization of ZEBRA LEAF16 Encoding a β-Hydroxyacyl-ACP Dehydratase in Rice

“…The central function of mitochondrial fatty acid synthesis is to maintain lipoic homeostasis, which is important for supporting photorespiration ( Ewald et al, 2007 ; Guan et al, 2015 ; Guan and Nikolau, 2016 ). Recently Guan et al (2017) showed that in both Arabidopsis mthad and mtkas mutants, the thylakoid membrane assembly is altered relative to their wild types, and is accompanied by the appearance of many small starch granules in the chloroplasts. The deformed chloroplasts are similar to those in the zl16 mutant here.…”

“…HAD homologs was difficult until the recent characterization of a mitochondrial HAD (mtHAD) in Arabidopsis . RNA interference (RNAi) mutants, with reduced mtHAD expression, exhibit traits such as a significantly reduced size of aerial organs, photorespiratory deficiency, altered chloroplastic starch granule morphology, and reduced catalytic activity of lipoylated enzymes ( Guan et al, 2017 ). Despite the clarification of the various HADs in the fatty acid biosynthesis of E. coli and Arabidopsis , the roles of HAD proteins in rice ( Oryza sativa ), a staple crop for over half of the world’s population and a monocot model plant, remain uncertain.…”

Proteomic analysis of differentially abundant proteins in the embryo and endosperm of Givotia moluccana (L.) Sreem

“…Hydroxyacyl-ACP dehydratase (spot 493D) (HAD), related to mitochondrial fatty acid synthesis, was specifically present in the endosperm and participates in the synthesis of unsaturated fatty acids and involved in the dehydration of long and short chain hydroxyl acyl-ACPS (Kastaniotis et al 2004). HAD also plays a key role in mitochondrial function and morphology in yeast and crucial for promoting photorespiration in plants (Guan et al 2017). Two protein spots identified as phenylalanine ammonia lyase (PAL) (spot 72A) and glutathione S-transferase DHAR2-like (GST) (spot 119a) were abundant in the embryo compared to the endosperm.…”