Diatom acclimation to elevated CO 2 via cAMP signalling and coordinated gene expression

Abstract

© 2015 Macmillan Publishers Limited. Diatoms are responsible for â 1/440% of marine primary productivity, fuelling the oceanic carbon cycle and contributing to natural carbon sequestration in the deep ocean. Diatoms rely on energetically expensive carbon concentrating mechanisms (CCMs) to fix carbon efficiently at modern levels of CO 2 (refs). How diatoms may respond over the short and long term to rising atmospheric CO 2 remains an open question. Here we use nitrate-limited chemostats to show that the model diatom Thalassiosira pseudonana rapidly responds to increasing CO 2 by differentially expressing gene clusters that regulate transcription and chromosome folding, and subsequently reduces transcription of photosynthesis and respiration gene clusters under steady-state elevated CO 2. These results suggest that exposure to elevated CO 2 first causes a shift in regulation, and then a metabolic rearrangement. Genes in one CO 2 -responsive cluster included CCM and photorespiration genes that share a putative cAMP-responsive cis-regulatory sequence, implying these genes are co-regulated in response to CO 2, with cAMP as an intermediate messenger. We verified cAMP-induced downregulation of CCM gene-CA3 in nutrient-replete diatom cultures by inhibiting the hydrolysis of cAMP. These results indicate an important role for cAMP in downregulating CCM and photorespiration genes under elevated CO 2 and provide insights into mechanisms of diatom acclimation in response to climate change