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THB 1, a truncated hemoglobin, modulates nitric oxide levels and nitrate reductase activity
Author(s) -
SanzLuque Emanuel,
OcañaCalahorro Francisco,
Montaigu Amaury,
ChamizoAmpudia Alejandro,
Llamas Ángel,
Galván Aurora,
Fernández Emilio
Publication year - 2015
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.12744
Subject(s) - nitrate reductase , chlamydomonas reinhardtii , hemoglobin , nitric oxide , nitrogen assimilation , chlamydomonas , biochemistry , biology , transcription factor , microbiology and biotechnology , assimilation (phonology) , nitrate , cell signaling , chemistry , signal transduction , enzyme , gene , mutant , ecology , linguistics , philosophy , endocrinology
Summary Hemoglobins are ubiquitous proteins that sense, store and transport oxygen, but the physiological processes in which they are implicated is currently expanding. Recent examples of previously unknown hemoglobin functions, which include scavenging of the signaling molecule nitric oxide ( NO ), illustrate how the implication of hemoglobins in different cell signaling processes is only starting to be unraveled. The extent and diversity of the hemoglobin protein family suggest that hemoglobins have diverged and have potentially evolved specialized functions in certain organisms. A unique model organism to study this functional diversity at the cellular level is the green alga Chlamydomonas reinhardtii because, among other reasons, it contains an unusually high number of a particular type of hemoglobins known as truncated hemoglobins ( THB 1– THB 12). Here, we reveal a cell signaling function for a truncated hemoglobin of Chlamydomonas that affects the nitrogen assimilation pathway by simultaneously modulating NO levels and nitrate reductase ( NR ) activity. First, we found that THB 1 and THB 2 expression is modulated by the nitrogen source and depends on NIT 2, a transcription factor required for nitrate assimilation genes expression. Furthermore, THB 1 is highly expressed in the presence of NO and is able to convert NO into nitrate in vitro . Finally, THB 1 is maintained on its active and reduced form by NR , and in vivo lower expression of THB 1 results in increased NR activity. Thus, THB 1 plays a dual role in NO detoxification and in the modulation of NR activity. This mechanism can partly explain how NO inhibits NR post‐translationally.