Transcriptome-wide analysis of Chlorella reveals auxin-induced carotenogenesis pathway in green microalgae

Microalgae are a commercially viable route for the production of carotenoids. Chlorella sp. BR2 was treated with plant hormones indole-3-acetic acid, salicylic acid, abscisic acid and methyl jasmonate and screened for enhanced carotenoid production. Indole-3-acetic acid was the only hormone with an inductive effect on carotenoid accumulation. As such, transcriptome-wide changes following auxin treatment were profiled using RNA-Seq and expressed sequences reconstructed with de novo assembly. This revealed the active pathway components of auxin-induced carotenogenesis. Data analysis specified the differentially expressed genes involved in auxin biosynthesis and signal transduction, which hint at close, yet unique relationship to equivalent pathways in higher plants. Unlike in plants, the ancient ABP1/SCFSKP2A/IBR5-mediated pathways for auxin response likely acted as the primary signaling route in Chlorella. As carotenoids are precursors for abscisic acid and antagonists of reactive oxygen species, the findings suggest a potential link between auxin signaling and abiotic stress tolerance.