Identification of two plastid proteins in the dinoflagellate Alexandrium affine that are substantially down-regulated by nitrogen-depletion.
The formation of harmful algal blooms (HABs) by dinoflagellates has been correlated with the nitrogen load in coastal waters. Nitrogen is implicated as an important factor in the initiation and maintenance of phytoplankton blooms. To characterize the cellular response to nitrogen, 2DE was used to compare protein expressions from dinoflagellates grown under nitrogen depleted and nitrogen replete conditions. A total of 17 differentially expressed protein spots were found, nine of which showed a roughly 16-fold decrease in N-depleted conditions. Five of these nine spots were all identified as isoforms of the plastid Form II ribulose-1,5 bisphosphate carboxylase/oxygenase (Rubisco II), while an additional four protein spots with a molecular weight of 50 kDa were identified as isoforms of a novel protein named nitrogen-associated protein 50 (NAP50). NAP50 was located in the plastids as shown by the presence of an N-terminal plastid targeting leader sequence and by immunohistochemistry. Levels of both Rubisco II and NAP50 decrease sharply between 24 and 36 h following nitrogen depletion and the decrease can be blocked if the N source is replenished before degradation occurs. Both proteins are rapidly resynthesized if the nitrogen source is replenished after degradation has occurred. These results are a first step in the dissection of the behavior of the dinoflagellate proteome under nitrogen stress conditions and may provide new insights into the relationship between dinoflagellate blooms and the nitrogen budget.
Lee
Fred Wang-Fat
FW
The Proteomic Task Force, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong.
Morse
David
D
Lo
Samuel Chun-Lap
SC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004141:Dinoflagellida / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D015536:Down-Regulation; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D057097:Harmful Algal Bloom; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism*; D018087:Plastids / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020543:Proteome / Q000032:analysis; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D020033:Protein Isoforms; D020543:Proteome; D015800:Protozoan Proteins; D012333:RNA, Messenger; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen