Overexpression of medium-chain-length polyhydroxyalkanoates induces significant salt tolerance and fungal resistance in flax

Climate changes and human population growth force us to develop of the new crops exhibiting improved tolerance to salinity, drought, high temperatures. Polyhydroxyalkanoates are synthesized in bacteria in response to stress conditions. Thus, the purpose of this study was to evaluate the impact of medium-chain-length polyhydroxyalkanoates (mcl-PHA) in transgenic flax Linum usitatissimum L. on plant growth, physiology and resistance to biotic and abiotic stresses. Flax is a valuable crop plant cultivated in a temperate climate. The subjects of this study were flax plants obtained via overexpression of the medium-chain-length polyhydroxyalkanoate (mcl-PHA) synthase gene from Pseudomonas aeruginosa. Modified flax plants grown in salt stress conditions showed higher biomass in comparison to wild-type plants. Salt stress did not cause the degradation of chlorophylls and carotenoids in transgenic flax plants in comparison to wild-type plants. The tested engineered plants also showed twofold higher resistance to diseases caused by Fusarium oxysporum, the main flax pathogen. Synthesis of mcl-PHA influenced amino acids profile, thus reduced the contents of glutamate and slightly elevated proline and arginine level were determined especially in a selected line (#11), exhibiting the highest mcl-PHA level and the highest measured resistance to pathogenic fungi and salinity. Performed biochemical analyses did not indicate the statistically important changes in the level of metabolites with antioxidant properties as flavonoids and phenolic compounds. Finally, synthesis of mcl-PHAs, and accompanying enhanced reactive oxygen species (ROS) scavenging ability caused improvement of salt tolerance and fungal resistance in genetically modified flax plants. Because soil salinization remains a real problem in many areas of the world and Fusarium is the main pathogen for flax, the analyzed flax plants with overexpression of mcl-PHA synthase have high potential for agriculture, especially from an economic point of view.