Contribution of omega-3 fatty acid desaturase and 3-ketoacyl-ACP synthase II (KASII) genes in the modulation of glycerolipid fatty acid composition during cold acclimation in birch leaves

Abstract

Temperate and boreal tree species respond to low positive temperatures (LT) or a shortening of the photoperiod (SD) by inducing cold acclimation. One of the metabolic consequences of cold acclimation is an increase in fatty acid (FA) desaturation in membrane lipids, which allows functional membrane fluidity to be maintained at LT. The molecular mechanisms of FA desaturation were investigated in leaves of birch seedlings (Betula pendula) during cold acclimation. Four genes involved in FA biosynthesis were isolated: a 3-ketoacyl-ACP synthase II gene (BpKASII) involved in the elongation of palmitoyl-ACP to stearoyl-ACP, and three omega-3 FA desaturase genes (BpFAD3, BpFAD7, and BpFAD8) involved in the desaturation of linoleic acid (18:2) to alpha-linolenic acid (18:3). BpFAD7 was the main omega-3 FAD gene expressed in birch leaves, and it was down-regulated by LT under SD conditions. LT induced the expression of BpFAD3 and BpFAD8 and a synchronous increase in 18:3 occurred in glycerolipids. Changes in the photoperiod did not affect the LT-induced increase in 18:3 in chloroplast lipids (MGDG, DGDG, PG), but it modulated the LT response detected in extra-chloroplastic lipids (PC, PE, PI, PS). A decrease in the proportion of the 16-carbon FAs in lipids occurred at LT, possibly in relation to the regulation of BpKASII expression at LT. These results suggest that LT affects the whole FA biosynthesis pathway. They support a co-ordinated action of microsomal (BpFAD3) and chloroplast enzymes (BpFAD7, BpFAD8) in determining the level of 18:3 in extra-chloroplastic membranes, and they highlight the importance of dynamic lipid trafficking.

Temperature-sensitive Post-translational Regulation of Plant Omega-3 Fatty-acid Desaturases Is Mediated by the Endoplasmic Reticulum-associated Degradation Pathway

“…In plant cells, for instance, cooler temperatures are often associated with an increase in the production of polyunsaturated fatty acids (PUFAs) 4 such as linoleic and ␣-linolenic acids, both of which are thought to help maintain membrane fluidity because of their lower melting temperatures (2). In addition, cooler temperatures often result in changes in the type of glycerolipids present in plant membranes, as well as the content and position of fatty acids attached to the glycerol backbone (3)(4)(5). Collectively, these changes to the type and amount of glycerolipids and their associated fatty acid components represent a central part of the molecular adaptations of plants to temperature.…”

Cold-Induced Accumulation of ω-3 Polyunsaturated Fatty Acid in a Liverwort,Marchantia polymorphaL.

“…In higher plants, desaturation of fatty acids occurs for adaptation to low temperature. 23,24) In the liverwort, the content of unsaturated fatty acids was 82:3 AE 0:4% of total lipids at 5 C after 3 weeks, higher than at 25 C, 77:7 AE 1:7%. This suggests that desaturation of fatty acids was taking place in the liverwort for adaptation to low temperature, as in higher plants.…”

“…This coincides with reports that the ER !-3 desaturase (FAD3) activities of higher plants are coldinducible. 24,25) Enhanced accumulation of this mRNA can promote the desaturation of LA to ALA generally in Time ( plants. However, since the liverwort has a C20 PUFA biosynthesis pathway, the increase in MpFAD3 mRNA led to enhancement of EPA accumulation.…”

Soybean Fatty Acid Desaturation Pathway: Responses to Temperature Changes and Pathogen Infection

“…In birch (Betula pendula) seedlings exposed to low temperatures (+ 4 to -24 o C) increased 18:3 in the chloroplast membrane lipids (MGDG, DGDG and PG) were found in the leaves at colder temperatures. The higher 18:3 levels were associated with upregulated expression of the birch ω-3 desaturases, BpFAD3, BpFAD7 and BpFAD8 (Martz et al 2006). Transgenic tomato plants in which the microsomal omega-3 desaturases have been silenced have greatly reduced LeFAD3 transcripts, contain low levels of 18:3, higher levels of 18:2, and exhibit long-term heat tolerance at 36 o C (Wang et al 2010).…”