Physiological, transcriptomic and metabolomic responses of the marine diatom Phaeodactylum tricornutum to the auxin IAA

Abstract

Auxin, an essential phytohormone, is widely used to promote plant growth and development. However, the effect of auxin on diatoms and its mechanism remain underexplored. Here, we studied the impact of the auxin indole 3-acetic acid (IAA) on the marine diatom Phaeodactylum tricornutum and the underlying molecular mechanisms. We found that 5 μg L⁻¹ of IAA promotes the growth of P. tricornutum in a time-dependent manner, with the most pronounced effect observed after 96 h of treatment, resulting in a growth promotion rate of 10.6 %. Treatment with IAA increased the content of photosynthetic pigments, improved the photosynthetic efficiency, and decreased the activity of antioxidant enzymes. In addition, transcriptomics showed that IAA exposure leads to upregulation of a large number of differential genes (DEGs) in carbon fixation and porphyrin metabolism, several of which were verified by qPCR. Furthermore, corresponding metabolites of these pathways were also validated by metabolomic analysis. Thus, IAA exhibits growth-promotion effect on the diatom mainly through increasing photosynthetic carbon sequestration and the expression of genes in porphyrin synthesis. Our results provide key data on the action mechanism of IAA in promoting the growth of a diatom.