Metabolic symbiosis and the birth of the plant kingdom.
Eukaryotic cells are composed of a variety of membrane-bound organelles that are thought to derive from symbiotic associations involving bacteria, archaea, or other eukaryotes. In addition to acquiring the plastid, all Archaeplastida and some of their endosymbiotic derivatives can be distinguished from other organisms by the fact that they accumulate starch, a semicrystalline-storage polysaccharide distantly related to glycogen and never found elsewhere. We now provide the first evidence for the existence of starch in a particular species of single-cell diazotrophic cyanobacterium. We provide evidence for the existence in the eukaryotic host cell at the time of primary endosymbiosis of an uridine diphosphoglucose (UDP-glucose)-based pathway similar to that characterized in amoebas. Because of the monophyletic origin of plants, we can define the genetic makeup of the Archaeplastida ancestor with respect to storage polysaccharide metabolism. The most likely enzyme-partitioning scenario between the plastid's ancestor and its eukaryotic host immediately suggests the precise nature of the ancient metabolic symbiotic relationship. The latter consisted in the export of adenosine diphosphoglucose (ADP-glucose) from the cyanobiont in exchange for the import of reduced nitrogen from the host. We further speculate that the monophyletic origin of plastids may lie in an organism with close relatedness to present-day group V cyanobacteria.
Deschamps
Philippe
P
Université des Sciences et Technologies de Lille, Unité Mixte de Recherches 8576 du Centre National de la Recherche Scientifique, Cité Scientifique, Villeneuve d'Ascq, France.
Colleoni
Christophe
C
Nakamura
Yasunori
Y
Suzuki
Eiji
E
Putaux
Jean-Luc
JL
Buléon
Alain
A
Haebel
Sophie
S
Ritte
Gerhard
G
Steup
Martin
M
Falcón
Luisa I
LI
Moreira
David
D
Löffelhardt
Wolfgang
W
Raj
Jenifer Nirmal
JN
Plancke
Charlotte
C
d'Hulst
Christophe
C
Dauvillée
David
D
Ball
Steven
S
D000245:Adenosine Diphosphate Glucose / Q000378:metabolism; D005075:Biological Evolution; D002451:Cell Compartmentation / Q000235:genetics / Q000502:physiology; D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010802:Phylogeny; D010944:Plants / Q000235:genetics / Q000378:metabolism*; D013213:Starch / Q000378:metabolism*; D013559:Symbiosis / Q000235:genetics / Q000502:physiology*; D014532:Uridine Diphosphate Glucose / Q000378:metabolism
D000245:Adenosine Diphosphate Glucose; D013213:Starch; D005947:Glucose; D009584:Nitrogen; D014532:Uridine Diphosphate Glucose