Abstract
Acyl carrier proteins (ACPs) are a group of small acidic proteins functioning as important cofactors in the de novo synthesis of fatty acids. In Arabidopsis, ACPs are encoded by a small gene family comprising five plastid members, AtACP1 to AtACP5, and three mitochondrial members. The biological functions and the transcriptional responses to abiotic stresses of most AtACPs have yet to be elucidated. The present study extends previous findings and provides new knowledge on the function of ACPs by examining the responses of AtACP-encoding genes to several abiotic stresses and, in particular, the role of AtACP5 in the adaptation to salt stress. Phylogenetic analysis showed that AtACP1, AtACP2, AtACP3, and AtACP5 can be classified into one group and separated from a group comprising AtACP4 and ACP homologs from related species. Quantitative RT-PCR analysis revealed that the expression of AtACP1, AtACP2, and AtACP3 was induced by drought. Both iron deficiency and nitrogen starvation resulted in down-regulation of AtACP4. The most pronounced response was observed for AtACP5, the expression of which was dramatically decreased by salt stress. Knock-out of AtACP5 showed increased sensitivity to NaCl stress, whereas transgenic lines overexpressing AtACP5 displayed increased salt tolerance relative to the wild-type. Overexpression of AtACP5 further led to an altered composition of fatty acids, mainly a decrease of oleic acid (C18:1) and an increase of palmitic acid (C16:0), and to a lower Na+/K+ ratio when compared to the salt stressed wild-type. The comprehensive transcriptional information on the small plastid AtACP gene family in response to various abiotic stresses and the further investigation of the AtACP5 indicate that AtACP5 might be critical for salt tolerance through alterations of the composition of fatty acids and, subsequently, the Na+/K+ ratio.
Highlights
Due to their sessile life style, plants are unavoidably exposed to environmental stresses throughout their life cycle
This analysis subdivided the proteins into two clades with AtACP1, AtACP2, AtACP3, AtACP5 and most Acyl carrier proteins (ACPs) from Brassicaceae species comprising one clade, and AtACP4 and ACPs from species unrelated to Brassicaceae forming a second clade, suggesting that the divergence between AtACP4 and the other four AtACPs appeared early in evolution
We found that Arabidopsis plastidial ACPs are a highly conserved family of Fatty acid synthases (FASs) system proteins, which respond disparately to different stresses
Summary
Due to their sessile life style, plants are unavoidably exposed to environmental stresses throughout their life cycle. To deal with such constraints, plants have evolved mechanisms that allow for efficient adaption to an ever-changing environment. Acyl carrier proteins (ACPs) play a central role in de novo FA synthesis. Fatty acid synthases (FASs) can be separated into two distinct classes. Plant ACPs are small (9 kD) separated polypeptides with 70–80 mostly acidic residues, modified by the covalent attachment of 4 phosphopantetheine to a centrally localized serine (Wakil et al, 1983; Marrakchi et al, 2002). ACPs are central components of FASs, which covalently bind all fatty acyl intermediates. The synthetic cycle is repeated multiple times until saturated C16 or C18 acyl-ACPs are produced for utilization in membrane biosynthesis (Chan and Vogel, 2010)
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