ABSTRACT: Phaffia rhodozyma is an ideal microbial astaxanthin resource. However, the low productivity of astaxanthin in this yeast obstructs the process of industrial production. Although P. rhodozyma is isolated from plant material and the phytohormone has proved to be an effective stimulator for microbial production, the effects and mechanisms of phytohormones on astaxanthin synthesis in P. rhodozyma have been rarely reported. In this study, a concentration of down to 0.5 mg/L exogenous salicylic acid (SA) could promote biomass, astaxanthin content and yield by 20.8%, 95.8% and 135.3% in P. rhodozyma, respectively. Further transcriptomic analysis showed that SA could discriminate well the transcriptomic profile of P. rhodozyma cells. The differently expressed genes (DEGs) in P. rhodozyma cells between the SA-treatment and the SA-free groups were identified, and involved in astaxanthin and its competitive metabolite synthesis, material supply, biomolecules metabolism and transportation, anti-stress and signal transductions at a global-cell level. A regulation mechanism of astaxanthin synthesis induced by SA, including perception and transduction of the SA signal, expression regulations of the downstream genes by transcription factors, and cellular stress response to the SA, is put forward in this study. The polyamine transporter gene (PT), as an up-regulated DEG, was overexpressed in the P. rhodozyma to obtain the transformant Prh-PT-006. It was found that biomass, astaxanthin content and yield of the Prh-PT-006 under 0.5 mg/L SA treatment could reach 6.6 g/L, 0.35 mg/g DCW and 2.3 mg/L, 24.5%, 143.1% and 199.0% higher than the wild strain at the SA-free condition, respectively. The result will provide the engineering targets for constructing strains with high-yield of astaxanthin, and help to accelerate the industrialization process of microbial astaxanthin.
