Two Fatty Acid Desaturases, STEAROYL-ACYL CARRIER PROTEIN Δ⁹-DESATURASE6 and FATTY ACID DESATURASE3, Are Involved in Drought and Hypoxia Stress Signaling in Arabidopsis Crown Galls

Abstract

Agrobacterium tumefaciens-derived crown galls of Arabidopsis (Arabidopsis thaliana) contain elevated levels of unsaturated fatty acids and strongly express two fatty acid desaturase genes, v3 FATTY ACID DESATURASE3 (FAD3) and STEAROYL-ACYL CARRIER PROTEIN D 9-DESATURASE6 (SAD6). The fad3-2 mutant with impaired a-linolenic acid synthesis developed significantly smaller crown galls under normal, but not under high, relative humidity. This strongly suggests that FAD3 plays a role in increasing drought stress tolerance of crown galls. SAD6 is a member of the SAD family of as yet unknown function. Expression of the SAD6 gene is limited to hypoxia, a physiological condition found in crown galls. As no sad6 mutant exists and to link the function of SAD6 with fatty acid desaturation in crown galls, the lipid pattern was analyzed of plants with constitutive SAD6 overexpression (SAD6-OE). SAD6-OE plants contained lower stearic acid and higher oleic acid levels, which upon reduction of SAD6 overexpression by RNA interference (SAD6-OE-RNAi) regained wild-type-like levels. The development of crown galls was not affected either in SAD6-OE or SAD6-OE-RNAi or by RNA interference in crown galls. Since biochemical analysis of SAD6 in yeast (Saccharomyces cerevisiae) and Escherichia coli failed, SAD6 was ectopically expressed in the background of the well-known suppressor of salicylic acid-insensitive2 (ssi2-2) mutant to confirm the desaturase function of SAD6. All known ssi2-2 phenotypes were rescued, including the high stearic acid level. Thus, our findings suggest that SAD6 functions as a D 9-desaturase, and together with FAD3 it increases the levels of unsaturated fatty acids in crown galls under hypoxia and drought stress conditions.

The Nonspecific Lipid Transfer Protein AtLtpI-4 Is Involved in Suberin Formation of Arabidopsis thaliana Crown Galls

“…Hypoxic conditions and the phytohormones abscisic acid and ethylene induce drought stress-protective mechanisms, affecting the lipid composition in Arabidopsis (Arabidopsis thaliana) crown galls. For example, two desaturases, the stearoyl-acyl carrier protein desaturase SAD6 and the fatty acid desaturase FAD3, are highly expressed and enrich the unsaturated fatty acid pool, which helps in maintaining membrane integrity (Klinkenberg et al, 2014). Second, a suberin-containing periderm-like layer covers the surface of crown galls to minimize water loss and avoid pathogen invasion (Efetova et al, 2007).…”

Role of the Plasma Membrane in Saline Conditions: Lipids and Proteins

“…Further evidence supporting the involvement of the PM lipids in salt tolerance is that expression of genes coding for major membrane lipid biosynthetic enzymes and fatty acid desaturases demonstrate a possible relationship between the variations in membrane lipid composition and tolerance to stresses (Allakhverdiev et al, 1999;Huynh et al, 2012;Zhai et al, 2012). Moreover, the PM components have a pivotal role in cellular signal transduction under different stresses (Wang et al, 2008a;Lu et al, 2012;Klinkenberg et al, 2014;Ruelland et al, 2014). Salinity stress, like other stresses, is perceived at the PM, which then triggers intracellular-signaling cascades that modulate gene expression, and consequently responses leading to salt stress tolerance (Fig.…”

A Shoot-Specific Hypoxic Response of Arabidopsis Sheds Light on the Role of the Phosphate-Responsive Transcription Factor PHOSPHATE STARVATION RESPONSE1

“…Interestingly, a similar modification in fatty acid composition of phospholipids and galactolipids was reported for crown galls produced in Arabidopsis by infection with Agrobacterium tumefaciens. In this hypoxic tissue, the relative amounts of desaturated fatty acids accumulated, which was related to an increased expression of the STEAROYL-ACYL CARRIER PROTEIN D9-DESATURASE6 (SAD6; Klinkenberg et al, 2014). SAD6 belongs to the hypoxic core response (Mustroph et al, 2009), and the induction of its expression is most likely also the cause for the increased degree of lipid desaturation in our analysis (Supplemental Fig.…”