Regulation of Blackbeard expression. (A) Effect of nitrate limitation on the expression of the pLTRbkb-GUS-FcpA construct in transgenic P. tricornutum cells. Data represent the average with standard error from seven independent cultures after two weeks nitrate limitation (50 μM NO3-) compared to standard growth medium (882 μM NO3-). (B) Verification of Blackbeard transcriptional activation by semi-quantitative RT PCR in the cultures used for McrPCR. (C) McrPCR on Blackbeard and H4 and RPS controls using DNA extracted from P. tricornutum cells grown under normal and nitrate-limited conditions.