Аннотация:Lobosphaera incisa is a green microalga that accumulates high levels of the valuable omega-6 LC-PUFA
arachidonic acid (ARA, 20:4n-6) in triacylglycerols under nitrogen (N) starvation. LC-PUFA accumulation is a rare trait in photosynthetic microalgae with insufficiently understood physiological significance. In this study, RNAi wasattempted, for the first time in L. incisa, to produce knockdown lines for the Δ5 desaturase gene. Two lines, termed modified lines, which were isolated during screening for transgenic events, demonstrated alterations in their LC-PUFA profile, ARA-biosynthesis gene expression and lipid class distribution. In line M5-78, which appeared to
carry a mutation in the Δ6 elongase gene, LC-PUFA were substituted by 18:3n-6 in all glycerolipids. Line M2-35,for which the exact genetic background has not been established, displayed a dramatic reduction in 20:4n-6,concomitant with an augmented proportion of 18:1n-9, in particular in the extraplastidial membrane lipids and triacylglycerols. The physiological responses of the modified lines to stressful conditions were compared with the WT and the Δ5 desaturase mutant. In the N-replete cells of modified lines, the frequency of lipid droplets was reduced, while a number of starch grains increased, suggesting altered partitioning of assimilated carbon into reserve
products. Furthermore, both lines exhibited a reduction in triacylglycerol production under N deprivation and to recover from N starvation. Both lines demonstrated lower photosynthetic pigment contents, impairments in photosynthesis under a range of stressful conditions, and less efficient functioning of photoprotection under optimal conditions. Possible implications of FA modifications in the stress response of L. incisa are addressed.