Transcriptomic and proteomic analyses reveal mechanisms of long-term warming acclimation in Phaeocystis globosa

Phaeocystis globosa is a harmful algal bloom species with a heteromorphic life cycle. Nevertheless, the long-term adaptive responses of P. globosa to ocean warming remain poorly understood. In this study, we examined the responses of P. globosa to short-term (1 month) and long-term (2 years) warming. Under short-term warming, the life cycle shifted significantly, with the proportion of solitary cells increasing by ∼90% and colony numbers decreasing by ∼10%. While colony diameter remained unchanged, extracellular polysaccharide content and photosynthetic efficiency decreased significantly. Transcriptomic analysis revealed a significant downregulation of genes associated with photosynthesis and polysaccharide synthesis. In contrast, the long-term warming group exhibited a continued increase in solitary cells, a 3.5-fold increase in colony numbers accompanied by a ∼32% reduction in their diameter. Notably, while photosynthetic activity recovered to control levels, extracellular polysaccharide content did not fully recover and remained significantly lower than the control. Integrated omics analyses indicated that cells redirected energy allocation from extracellular polysaccharide production towards the synthesis of amino acids and fatty acids. These findings demonstrate that a strategic shift in carbon and energy investment from structural components to metabolic precursors is a key adaptive strategy of P. globosa to warming.