Initiation of efficient <scp> C <sub>4</sub> </scp> pathway in response to low ambient <scp> CO <sub>2</sub> </scp> during the bloom period of a marine dinoflagellate
Hao Zhang, Youping Zhou, Tianqi Liu, Xijie Yin, Lin Lin, Qiang Lin, Da‐Zhi Wang
Abstract
Summary Dinoflagellates are important primary producers and major causative agents of harmful algal blooms in the global ocean. Despite the great ecological significance, the photosynthetic carbon acquisition by dinoflagellates is still poorly understood. The pathways of photosynthetic carbon assimilation in a marine dinoflagellate Prorocentrum donghaiense under both in situ and laboratory‐simulated bloom conditions were investigated using a combination of metaproteomics, qPCR, stable carbon isotope and targeted metabolomics approaches. A rapid consumption of dissolved CO 2 to generate high biomass was observed as the bloom proceeded. The carbon assimilation genes and proteins including intracellular carbonic anhydrase 2, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase and RubisCO as well as their enzyme activities were all highly expressed at the low CO 2 level, indicating that C 4 photosynthetic pathway functioned in the blooming P . donghaiense cells. Furthermore, δ 13 C values and content of C 4 compound (malate) significantly increased with the decreasing CO 2 concentration. The transition from C 3 to C 4 pathway minimizes the internal CO 2 leakage and guarantees efficient carbon fixation at the low CO 2 level. This study demonstrates the existence of C 4 photosynthetic pathway in a marine dinoflagellate and reveals its important complementary role to assist carbon assimilation for cell proliferation during the bloom period.