Effect of High Temperature and Drought on the Fatty Acid Composition of Oil of Different Linseed Varieties and Its Association with Gene Expression

Flax is an important food and industrial crop. Linolenic acid (LIN) content of linseed oil differs greatly among varieties, ranging from 2% to 70%. In addition to genetic factors, environmental conditions can also significantly impact the fatty acid composition of linseed oil. Our study aimed to compare the effects of different temperature and watering conditions on the fatty acid composition of oil from nine flax varieties with diverse LIN content induced by genotype. Elevated temperature with reduced watering resulted in increased oleic acid (OLE) levels in all varieties. Decreases in linoleic acid (LIO) and LIN were also observed, though these trends were less pronounced in genotypes with low LIN content. Using our previously obtained transcriptomic data for seeds of the same flax varieties grown under the same conditions, we found that elevated temperature with reduced watering caused the maximum expression levels to shift to earlier development stages and shortened the period of high expression for the key fatty acid desaturase (FAD) genes: FAD2a-1, FAD2a-2, and FAD2b-2 (OLE to LIO desaturation) as well as FAD3a and FAD3b (LIO to LIN desaturation). However, low-LIN flax genotypes have inactivating mutations in FAD3a and FAD3b, so FAD3d-1, FAD3d-2, FAD3c-1, and FAD3c-2 were likely the major contributors to LIN synthesis in these varieties. These FAD3 genes had low but relatively stable expression levels during seed development compared to FAD3a and FAD3b, which may explain why growth conditions had less effect on LIN content in low-LIN genotypes. High temperature with optimal watering also led to a significant increase in OLE content in flax seeds. Thus, the fatty acid composition of linseed oil is significantly altered at high temperature, which is associated with a shift to earlier stages and narrowing of the expression peaks of key FAD genes in seeds. These findings should be considered when cultivating flax and producing pharmaceuticals, food, paints, and other products from its seeds.