Abstract
Linolenic acid (Ln) released from chloroplast membrane galactolipids is a precursor of the phytohormone jasmonic acid (JA). The involvement of this hormone in different plant biological processes, such as responses to biotic stress conditions, has been extensively studied. However, the role of Ln in the regulation of gene expression during abiotic stress situations mediated by cellular redox changes and/or by oxidative stress processes remains poorly understood. An RNA-seq approach has increased our knowledge of the interplay among Ln, oxidative stress and ROS signaling that mediates abiotic stress conditions. Transcriptome analysis with the aid of RNA-seq in the absence of oxidative stress revealed that the incubation of Arabidopsis thaliana cell suspension cultures (ACSC) with Ln resulted in the modulation of 7525 genes, of which 3034 genes had a 2-fold-change, being 533 up- and 2501 down-regulated genes, respectively. Thus, RNA-seq data analysis showed that an important set of these genes were associated with the jasmonic acid biosynthetic pathway including lypoxygenases (LOXs) and Allene oxide cyclases (AOCs). In addition, several transcription factor families involved in the response to biotic stress conditions (pathogen attacks or herbivore feeding), such as WRKY, JAZ, MYC, and LRR were also modified in response to Ln. However, this study also shows that Ln has the capacity to modulate the expression of genes involved in the response to abiotic stress conditions, particularly those mediated by ROS signaling. In this regard, we were able to identify new targets such as galactinol synthase 1 (GOLS1), methionine sulfoxide reductase (MSR) and alkenal reductase in ACSC. It is therefore possible to suggest that, in the absence of any oxidative stress, Ln is capable of modulating new sets of genes involved in the signaling mechanism mediated by additional abiotic stresses (salinity, UV and high light intensity) and especially in stresses mediated by ROS.
Highlights
The poly-unsaturated fatty acid α-Linolenic acid (Ln), with an 18-carbon chain and three cis double bonds, is an essential omega-3 fatty acid and organic compound found in seeds such as flaxseed, chia, soybean and various vegetable oils.Ln, which can be released from several complex fatty acids mainly located in the membranes of organelles such as chloroplast is a precursor of the jasmonic acid (JA) phytohormone and, of the oxylipin pathway
As Ln is the jasmonic acid precursor and the major fatty acid in A. thaliana cell suspension cultures (ACSC) and www.frontiersin.org given that Ln-treatment did not cause oxidative damage in ACSC, it was selected for this study
LINOLENIC ACID-RESPONSIVE GENES IN OXIDATIVE STRESS SITUATIONS With the aid of this transcriptomic analysis, we found a large amount of heat shock proteins (HSPs) and heat shock transcription factors (HSFs) associated with the responses to hydrogen peroxide (H2O2), accounting for 25.68% of total genes up-regulated (AT1G52560, AT2G26150, AT4G25200, AT2G20560, AT2G32120, AT1G74310, AT5G37670, AT4G21320, and AT1G16030) (Figure 5)
Summary
Ln, which can be released from several complex fatty acids mainly located in the membranes of organelles such as chloroplast is a precursor of the jasmonic acid (JA) phytohormone and, of the oxylipin pathway. The oxygenation of Ln is the initial step in JA biosynthesis which is carried out by plastid-located lipoxygenases (LOXs) at C-13 and is followed by the dehydration of 13-hydroperoxy-octadecatrienoic acid caused by allene oxide synthase (AOS). The unstable epoxide generated is cyclized stereospecifically and converted into 12-oxo-phytodienoic acid (OPDA) by allene oxide cyclase (AOC) followed by the reduction of OPDA to 3-oxo-2-(2 (Z)-pentenyl)-cyclopentane-1 octanoic acid by the Arabidopsis OPDA reductase (OPR3). The subsequent shortening of the carboxylic acid side chain is caused by the fatty acid β–oxidation machinery and is initiated by Acyl-CoA-oxydase (ACX1) (Wasternack and Hause, 2013; Wasternack, 2014b)
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