In silico and biochemical analysis of Physcomitrella patens photosynthetic antenna: Identification of subunits which evolved upon land adaptation

Abstract

Background: In eukaryotes the photosynthetic antenna system is composed of subunits encoded by the light harvesting complex (Lhg) 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. Principal Findings: In this study, we characterized the antenna protein multigene family in physcomitrella patens, by sequence analysis as well as biohemical 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 rolel in adaptation to the: sub-aerial environment. Our functional analysis which: showed that photo-protective mechanisms in Physcomitrella patens arevery similar to those in seed plants fits with this hypothesis In particular, In Physcomitrella patens also activates Non Photochemical Quenching Upon illumination, cosistent 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, fluorecence 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. © 2008 Alboresi et al.