Rapid remodeling of lipids and transcriptome in the diatom Phaeodactylum tricornutum in response to defense related decadienal

Diatoms rapidly release extracellular oxylipins (oxygenated lipids) including polyunsaturated aldehydes (PUAs) upon cell damage, as a defense response to inhibit reproduction in many herbivores. PUAs are synthesized from membrane phospholipids. In diatoms, PUAs rapidly increase intracellular Ca²⁺ and nitric oxide (NO) levels and affect gene expression and physiology. Treatment of the marine diatom Phaeodacylum tricornutum, with the PUA, decadienal (DD, 10 μM) altered lipid compositions. In cells treated for 3 hr, nine out of ten measured saturated and unsaturated fatty acids declined (range of 0.5-0.7 fold of solvent control levels). At 6 hr, most fatty acid species 14:0, 18:0, 20:5 remained at lower levels while 18:1 and 18:2 increased (1.12 fold and 1.46 fold respectively). Phospholipids in DD treated cells at 3 hr showed decline in PG¹ (0.69 fold) and PS¹ (0.36 fold) whereas PE¹ increased (1.79 fold). At 6 hr, PI¹ (0.79 fold), PS¹ (0.28 fold) and LPG¹ (0.56 fold) declined whereas PC¹ (1.21 fold) and PE¹ (2.7 fold) increased. There were no effects on abundant chloroplast glycolipids (DGDG/MGDG)¹. Molecular species composition of phospholipids showed a greater decline in polyunsaturated fatty acids than monounsaturated fatty acids and saturated fatty acids, which indicates a shift towards saturated fatty acids that may protect membranes from oxidative stress. C-28 brassicasterol declined 0.86 fold at 3hr whereas there was no change at 6hr. Non-polar lipids increased by 1.16 fold and 1.38 fold at 3hr and 6hr. Decreased membrane permeability in DD treated cells was suggested by reduced uptake of cytological dyes. To our knowledge, this is the first report documenting novel rapid (within 6 hr) phospholipid changes in response to PUA suggesting early membrane lipid remodeling to aid in adaptation to PUA stress in algae. Transcriptome analysis at 3hr and 6hr of DD treatment indicated differential regulation of a subset of genes in fatty acid metabolism pathway in co-ordination with genes in multiple metabolic pathways. This suggests that rapid lipid remodeling may be regulated at transcriptome levels to help adapt to decadienal stress.Plant Biolog