Arginine is a component of the ammonium- CYG56 signalling cascade that represses genes of the nitrogen assimilation pathway in Chlamydomonas reinhardtii
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Autor
González-Ballester, David
Sanz-Luque, Emanuel
Galván Cejudo, Aurora
Fernández Reyes, Emilio
Montaigu, Amaury de
Editor
Public Library of ScienceFecha
2018Materia
Nitrogen metabolismNitrogen assimilation
Chlamydomonas
CYG56
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Nitrogen assimilation and metabolism are essential processes for all living organisms, yet
there is still much to be learnt on how they are regulated. The use of Chlamydomonas reinhardtii
as a model system has been instrumental not only in identifying conserved regulation
mechanisms that control the nitrogen assimilation pathway, but also in understanding how
the intracellular nitrogen status regulates metabolic processes of industrial interest such as
the synthesis of biolipids. While the genetic regulators that control the nitrogen pathway are
successfully being unravelled, other layers of regulation have received less attention. Amino
acids, for example, regulate nitrogen assimilation in certain organisms, but their role in Chlamydomonas
has not thoroughly been explored. Previous results had suggested that arginine
might repress key genes of the nitrogen assimilation pathway by acting within the
ammonium negative signalling cascade, upstream of the nitric oxide (NO) inducible guanylate
cyclase CYG56. We tested this hypothesis with a combination of genetic and chemical
approaches. Antagonising the effects of arginine with an arginine biosynthesis mutant or
with two chemical analogues released gene expression from ammonium mediated repression.
The cyg56 and related non1 mutants, which are partially insensitive to ammonium
repression, were also partially insensitive to repression by arginine. Finally, we show that
the addition of arginine to the medium leads to an increase in intracellular NO. Our data
reveal that arginine acts as a negative signal for the assimilation of nitrogen within the
ammonium-CYG56 negative signalling cascade, and provide a connection between amino
acid metabolism and nitrogen assimilation in microalgae.