Physiological and molecular responses of Prorocentrum donghaiense to dissolved inorganic phosphorus limitation

Prorocentrum donghaiense is an important dinoflagellate as it frequently forms harmful algal blooms that cause serious damage to marine ecosystems and fisheries in the coast of East China Sea. Previous studies showed that phosphorus acquisition (especially inorganic phosphorus) was the limiting factor for P. donghaiense growth. However, the responsive mechanism of this microalga under dissolved inorganic phosphorus (DIP) limitation is poorly understood. In this work, the physiological parameters and differentially expressed genes in P. donghaiense response to DIP limitation were comparatively analyzed. DIP-depleted P. donghaiense displayed decreased growth rate, enlarged cell size, decreased cellular phosphorus content, and high AP activities. A forward suppression subtractive hybridization (SSH) library representing differentially upregulated genes in P. donghaiense under DIP-depleted conditions was constructed, and 134 ESTs were finally identified, with a significant identity (E values < 1 x 10(-4)) to the deposited genes (proteins) in the corresponding databases. Five representative genes, namely, NAD-dependent deacetylase, phosphoglycolate phosphatase, heat shock protein (HSP) 90, rhodopsin, and HSP40 were investigated through real-time quantitative PCR to verify the effectiveness of the established SSH library. Results showed that all the selected genes were differentially expressed and thus indicated that the established SSH library generally represented differentially expressed genes. These genes were classified into 11 categories according to their gene ontology annotations of biological processes. The members involved in functional responses such as cell defense/homeostasis, phosphorus metabolism, and cellular cycles were specially discussed. This study is the first to perform a global analysis of differentially expressed functional genes in P. donghaiense under DIP-depleted condition. It provided new insights into the molecular adaptive mechanisms of dinoflagellate in response to phosphorous limitation and elucidating the formation mechanism of algal blooms.