Proteomic Response Of Alexandrium Catenella To Ambient Phosphorus Depletion And Resupplement

Alexandrium catenella is a worldwide distributed dinoflagellate species.Studies have shown that phosphorus(P)is a limiting nutrient for cell growth and bloom formation of A.catenella.Much effort has been devoted to eco-physiological responses of A.catenella to ambient P-depletion,however,little is known about the molecular mechanism,particularly at the protein level.This study,applied the quantitative proteomic approach:Isobaric tags for relative and absolute quantitation(iTRAQ)to compare protein expression profiles of A.catenella under different P consitions,characterized the differentially expressed proteins,analyzed their functions and biological processes,identified proteins related to P metabolism and discussed the adaptative strategies of A.catenellato P-depletion and the response mechanism to the resupplement of different P sources,combined with physiological parameter analysis.The main results were as follows:(1)A.catenella cells were able to utilize the intracellular "stored P" to maintain cell growth when ambient P became depletion.After resupplement of different P sources,A.catenella cells rapidly absorbed both inorganic and organic P.Compared with organic P,glucose-6-phosphate(G-6-P),the uptake of inorganic P,Na2HPO4 was faster,but no significant difference on cell growth between the two species.(2)Cell density of A.catenella maintained relatively stable under P-depleted condition,and alkaline phosphatase activity(APA)increased rapidly.After resupplement of P,A.catenella cells recovered growth rapidly and APA decreased.Compared with Na2HPO4,the effect of G-6-P on APA took more time.In Na2HPO4 resupplement group,APA decreased immediately,while in G-6-P resupplement group,APA increased firstly,then decreased,suggesting that the different utilization strategies of A.catenella to Na2HPO4 and G-6-P.(3)A total of 6,577 high-confidence proteins were identified from A.catenella,among them,proteins involved in ribosome,glycolysis/gluconeogenesis,purine metabolism and two-component system were more abundant.In P-depleted condition,A.catenella could induce or up-regulate the expressions of acid phosphatase and other phosphoesterase,utilize organic phosphorus and non-phospholipids-sphingolipids instead of phospholipids to reduce cell demand for P.In addition,protein translations,carbon fixation,nitrogen metabolism,sulfur metabolism and other important biological processes were down-regulated to adjust energy allocation to adapt to ambient P-depletion.(4)A.catenella could quickly recover the growth after addition of Na2HPO4 or G-6-P,but a great difference was observed between the two treatments.A.catenella absorbed Na2HPO4 rapidly compare to G-6-P,but more biological processes changed in DOP-resupplement cells than that in DIP-resupplement cells.Nucleic acid metabolism and other biological processes were significantly up-regulated in DOP-resupplement cells.A.catenella might possess special mechanism to utilize G-6-P:it might directly utlize G-6-P for the synthesis of nucleic acid through the pentose phosphate pathway.(5)P metabolism related proteins,such as acid phosphatase,5'-nucleotidase,were identified in A.catenella.These proteins played a vital role in adaption to ambient P-depletion and in response to the resupplement of different P species.