Phytohormones as stimulators to improve arachidonic acid biosynthesis in Mortierella alpina

Phytohormones are chemical messengers that have a positive effect at low concentrations on the biosynthesis of high-value compounds. Therefore, the effects of phytohormones on lipid and arachidonic acid (ARA) biosynthesis in Mortierella alpina were investigated in this study. At proper concentrations, the stimulatory effects of phytohormones on lipid production were determined to be as follows: 6-benzyl adenine (BA) > indole-3-acetic acid (IAA) > furfuryl adenine (KT) > gibberellin (GA) > indole-3-butyric acid (IBA) > abscisic acid (ABA). The results show that in the presence of 15 mg L-1 BA, the best positive effect was obtained, in which the lipid and ARA yields of M. alpina increased by 20.34% and 29.17%, respectively. Surprisingly, there was no synergy between the addition of two cytokinins (KT and BA), while adding cytokinins (KT or BA) and auxin (IAA) inhibited the growth of M. alpina and the ARA yield decreased by approximately 64%. Additional studies, such as those involving enzyme activity detection and quantitative real time polymerase chain reaction were carried out to check the fatty acid and lipid biosynthesis when the phytohormones were present. The activity of the main NADPH-supplying enzyme, 6-phosphoglucose dehydrogenase (G6PDH), increased by 19.52%. Moreover, the transcription levels of fatty acid synthase (FAS), Delta 9-desaturase, and diacylglycerolacyltransferase (DGAT) increased by 9.3, 9.6 and 7.7 times, respectively, when only one type of phytohormone was present, indicating the enhancement of fatty acid and lipid biosynthesis in M. alpina. This study demonstrates the potential application of phytohormones for improving ARA yields of M. alpina.