In silico and biochemical analysis of Physcomitrella patens photosynthetic antenna: identification of subunits which evolved upon land adaptation.
BACKGROUND
In eukaryotes the photosynthetic antenna system is composed of subunits encoded by the light harvesting complex (Lhc) multigene family. These proteins play a key role in photosynthesis and are involved in both light harvesting and photoprotection. The moss Physcomitrella patens is a member of a lineage that diverged from seed plants early after land colonization and therefore by studying this organism, we may gain insight into adaptations to the aerial environment.


RESULTS
In this study, we characterized the antenna protein multigene family in Physcomitrella patens, by sequence analysis as well as biochemical and functional investigations. Sequence identification and analysis showed that some antenna polypeptides, such as Lhcb3 and Lhcb6, are present only in land organisms, suggesting they play a role in adaptation to the sub-aerial environment. Our functional analysis which showed that photo-protective mechanisms in Physcomitrella patens are very similar to those in seed plants fits with this hypothesis. In particular, Physcomitrella patens also activates Non Photochemical Quenching upon illumination, consistent with the detection of an ortholog of the PsbS protein. As a further adaptation to terrestrial conditions, the content of Photosystem I low energy absorbing chlorophylls also increased, as demonstrated by differences in Lhca3 and Lhca4 polypeptide sequences, in vitro reconstitution experiments and low temperature fluorescence spectra.


CONCLUSIONS
This study highlights the role of Lhc family members in environmental adaptation and allowed proteins associated with mechanisms of stress resistance to be identified within this large family.
Alboresi
Alessandro
A
Laboratoire de Génétique et Biophysique des Plantes-UMR 6191 CEA-CNRS-Université de la Méditerranée, Marseille, France.
Caffarri
Stefano
S
Nogue
Fabien
F
Bassi
Roberto
R
Morosinotto
Tomas
T
D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D019068:Bryopsida / Q000737:chemistry*; D019295:Computational Biology; D017124:Conserved Sequence; D019143:Evolution, Molecular; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry; D008954:Models, Biological; D008969:Molecular Sequence Data; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry; D010802:Phylogeny; D021122:Protein Subunits / Q000378:metabolism*; D020539:Sequence Analysis, Protein; D020524:Thylakoids; D024341:Xanthophylls
D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D021122:Protein Subunits; D024341:Xanthophylls