Comparative Lipidomic Analysis Reveals Heat Stress Responses of Two Soybean Genotypes Differing in Temperature Sensitivity

Heat-induced changes in lipidome and their influence on stress adaptation are not well-defined in plants. We investigated if lipid metabolic changes contribute to differences in heat stress responses in a heat-tolerant soybean genotype DS25-1 and a heat-susceptible soybean genotype DT97-4290. Both genotypes were grown at optimal temperatures (OT; 30/20 °C) for 15 days. Subsequently, half of the plants were exposed to heat stress (38/28 °C) for 11 days, and the rest were kept at OT. Leaf samples were collected for lipid and RNA extractions on the 9th and 11th days of stress, respectively. We observed a decline in the lipid unsaturation level due to a decrease in the polyunsaturated linolenic acid (18:3) content in DS25-1. When examined under OT conditions, DS25-1 and DT97-4290 showed no significant differences in the expression pattern of the Fatty Acid Desaturase (FAD) 2-1A, FAD2-2B, FAD2-2C, FAD3A genes. Under heat stress conditions, substantial reductions in the expression levels of the FAD3A and FAD3B genes, which convert 18:2 lipids to 18:3, were observed in DS25-1. Our results suggest that decrease in levels of lipids containing 18:3 acyl chains under heat stress in DS25-1 is a likely consequence of reduced FAD3A and FAD3B expression, and the decrease in 18:3 contributes to DS25-1′s maintenance of membrane functionality and heat tolerance

Alterations in the leaf lipidome of \u3ci\u3eBrassica carinata\u3c/i\u3e under high-temperature stress

Background: Brassica carinata (A) Braun has recently gained increased attention across the world as a sustainable biofuel crop. B. carinata is grown as a summer crop in many regions where high temperature is a significant stress during the growing season. However, little research has been conducted to understand the mechanisms through which this crop responds to high temperatures. Understanding traits that improve the high-temperature adaption of this crop is essential for developing heat-tolerant varieties. This study investigated lipid remodeling in B. carinata in response to high-temperature stress. A commercial cultivar, Avanza 641, was grown under sunlit-controlled environmental conditions in Soil-Plant-Atmosphere-Research (SPAR) chambers under optimal temperature (OT; 23/ 15°C) conditions. At eight days after sowing, plants were exposed to one of the three temperature treatments [OT, high-temperature treatment-1 (HT-1; 33/25°C), and high-temperature treatment-2 (HT-2; 38/30°C)]. The temperature treatment period lasted until the final harvest at 84 days after sowing. Leaf samples were collected at 74 days after sowing to profile lipids using electrospray-ionization triple quadrupole mass spectrometry. Results: Temperature treatment significantly affected the growth and development of Avanza 641. Both hightemperature treatments caused alterations in the leaf lipidome. The alterations were primarily manifested in terms of decreases in unsaturation levels of membrane lipids, which was a cumulative effect of lipid remodeling. The decline in unsaturation index was driven by (a) decreases in lipids that contain the highly unsaturated linolenic (18: 3) acid and (b) increases in lipids containing less unsaturated fatty acids such as oleic (18:1) and linoleic (18:2) acids and/or saturated fatty acids such as palmitic (16:0) acid. A third mechanism that likely contributed to lowering unsaturation levels, particularly for chloroplast membrane lipids, is a shift toward lipids made by the eukaryotic pathway and the channeling of eukaryotic pathway-derived glycerolipids that are composed of less unsaturated fatty acids into chloroplasts. Conclusions: The lipid alterations appear to be acclimation mechanisms to maintain optimal membrane fluidity under high-temperature conditions. The lipid-related mechanisms contributing to heat stress response as identified in this study could be utilized to develop biomarkers for heat tolerance and ultimately heat-tolerant varieties

Physiological and Lipidomic Characterization of Heat Response in Peanut

Peanut (Arachis hypogea L.) is an important crop grown worldwide for its nutritional value and economic significance. Reducing the costs of production and improving profitability are major goals of the peanut industry. However, increasing global temperatures present a serious challenge to achieving these goals. Peanut plants are highly sensitive to heat stress during flowering stage due to poor pollen performance that results in reduced fruit-set and yield. The objective of this study was to evaluate the anther lipidome of peanut cultivars to identify specific lipid traits or species that are associated with better pollen performance under heat stress. Six peanut cultivars with varying degrees of drought and/or heat tolerance were evaluated in a field study under open field (control) and heat stress (HT) conditions in Summer 2018. Heat tents were used to impose heat stress when the last cultivar reached anthesis. Stress treatment lasted for 17 days. Peanut anthers were collected on the 13th day of stress. Anther lipid profiling was done using electrospray ionization-triple quadrupole mass spectrometry (ESI-MS/MS). Chlorophyll fluorescence, chlorophyll index, and pollen viability were also measured during the stress period. After the stress period ended, all plants were kept under open field conditions until final harvest at maturity. Preliminary results showed that significant effect of treatment and/or cultivar were found on chlorophyll index and maximum quantum yield of PSII. Based on these traits, Tifguard was the most stress-tolerant and Bailey was the most stress-susceptible cultivar. Heat stress decreased the unsaturation levels of polar lipids. Generally, Tifguard maintained a lower and Bailey a higher level of polar lipid unsaturation. Within the framework of the current knowledge on lipid metabolism, these results suggest that lowering the lipid unsaturation levels under HT conditions is a mechanism associated with the contrasting responses to HT of these cultivars

Head-Group Acylation of Chloroplast Membrane Lipids

Head group-acylated chloroplast lipids were discovered in the 1960s, but interest was renewed about 15 years ago with the discovery of Arabidopsides E and G, acylated monogalactosyldiacylglycerols with oxidized fatty acyl chains originally identified in Arabidopsis thaliana. Since then, plant biologists have applied the power of mass spectrometry to identify additional oxidized and non-oxidized chloroplast lipids and quantify their levels in response to biotic and abiotic stresses. The enzyme responsible for the head-group acylation of chloroplast lipids was identified as a cytosolic protein closely associated with the chloroplast outer membrane and christened acylated galactolipid-associated phospholipase 1 (AGAP1). Despite many advances, critical questions remain about the biological functions of AGAP1 and its head group-acylated products

Additional file 1 of Alterations in the leaf lipidome of Brassica carinata under high-temperature stress

Additional file 1: Table S1. Data on 105 lipid analytes as normalized intensity per milligrams of leaf dry weight. Table S2. Analysis of variance results on the effects of temperature treatments on lipid head-group unsaturation indices, lipid molecular species, and levels of head-group class sub-pools

Additional file 1 of Alterations in the leaf lipidome of Brassica carinata under high-temperature stress

Additional file 1: Table S1. Data on 105 lipid analytes as normalized intensity per milligrams of leaf dry weight. Table S2. Analysis of variance results on the effects of temperature treatments on lipid head-group unsaturation indices, lipid molecular species, and levels of head-group class sub-pools