Unique Peripheral Antennas in the Photosystems of the Streptophyte Alga Mesostigma Viride

Abstract

Land plants evolved from a single group of streptophyte algae. One of the key factors needed for adaptation to a land environment is the modification of the peripheral antenna systems of photosystems. Here, the photosystems of Mesostigma viride, an earliest-branched streptophyte alga, were analyzed to gain insight into their evolution.Iso-seq and phylogenetic analyses of Light-Harvesting Complexes (LHCs) revealed that M. viride possesses three algae-specific LHCs, including algae-type LHCA2, LHCA9, and LHCP; while the streptophyte-specific LHCB6 was not identified. These data suggest that the acquisition of LHCB6 and the loss of algae-type LHCs occurred after the M. viride lineage branched off from other streptophytes. Clear-native (CN)-PAGE [Results]Separation of photosystems by ClearNative (CN)-PAGE Clear-Native (CN)-PAGE is a powerful technique that enables one to separate protein complexes while retaining their structure. Here, the M. viride photosystems were separated using amphipol-based CN-PAGE (Furukawa et al., 2019) after solubilization with a mild detergent, dodecyl maltoside (α-DDM). As a result, the PSI-PSII megacomplex, the PSII-LHCII supercomplexes, the PSI-LHCI-LHCII bands, the PSI-LHCI, and the LHCII trimer were resolved (Fig. 1A). The identification of the separated bands was accomplished using 2D-CN/SDS-PAGE followed by immunoblot analysis (Fig. 1B) and silver-staining (Fig. 1C), as described in previous studies (Järvi et al., 2011; Takabayashi et al., 2011). The identification of two PSI-LHCI-LHCII bands were confirmed by further analysis described in a later section of this report. The overall band profile (Fig. 1A) was similar to the profile for P. patens presented by Furukawa et al. ( 2019), however, a substantial difference was evident for PSI-LHCI-LHCII. Two PSI-LHCI-LHCII bands were found in M. viride (Fig. 1A), whereas only one PSI-LHCI-LHCII band was found in the profile of P. patens presented by Furukawa et al.