Symbiosis modulates response to starvation in a model cnidarian
Mutualistic symbioses between cnidarians and photosynthetic algae (family Symbiodiniaceae) are modulated by complex interactions between host immunity and environmental conditions. The sequences submitted here are part of an investigation into how symbiosis and starvation interact to influence gene expression and stress response programming in the sea anemone Exaiptasia pallida (Aiptasia). Aposymbiotic Aiptasia exhibited stronger transcriptomic responses to starvation than symbiotic conspecifics, suggesting that symbiosis buffers starvation stress. Contrasting previous studies in the nonsymbiotic anemone Nematostella vectensis, starvation led to increased protein levels of transcription factor NF-kappaB, associated gene pathways, and putative target genes, but decreased expression of oxidative stress pathways, in symbiotic and aposymbiotic Aiptasia. Yet, the upregulated NF-kappaB pathway was not predictive of susceptibility to pathogen or ROS stress. Furthermore, starvation had differing effects on Aiptasia susceptibility to these two stressors. Finally, Aiptasia starvation responses were contrasted to those of a facultative coral (Oculina arbuscula) and N. vectensis. Aiptasia "defense" responses were regulated similarly to O. arbuscula, but not N. vectensis, suggesting that capacity for symbiosis influences starvation responses in cnidarians. In summary, expression of certain immune pathways - especially those previously associated with maintaining cnidarian-algal symbioses - does not necessarily reflect proportional susceptibility to stressors, highlighting the complexities of cnidarian immunity across symbiotic states and energetic priorities.