Plants harvest light energy utilized for photosynthesis by light-harvesting complex I and II (LHCI and LHCII) surrounding photosystem I and II (PSI and PSII), respectively. During the evolution of green plants, moss is at an evolutionarily intermediate position from aquatic photosynthetic organisms to land plants, being the first photosynthetic organisms that landed. Here, we report the structure of the PSI–LHCI supercomplex from the moss Physcomitrella patens (Pp) at 3.23 Å resolution solved by cryo-electron microscopy. Our structure revealed that four Lhca subunits are associated with the PSI core in an order of Lhca1–Lhca5–Lhca2–Lhca3. This number is much decreased from 8 to 10, the number of subunits in most green algal PSI–LHCI, but the same as those of land plants. Although Pp PSI–LHCI has a similar structure as PSI–LHCI of land plants, it has Lhca5, instead of Lhca4, in the second position of Lhca, and several differences were found in the arrangement of chlorophylls among green algal, moss, and land plant PSI–LHCI. One chlorophyll, PsaF–Chl 305, which is found in the moss PSI–LHCI, is located at the gap region between the two middle Lhca subunits and the PSI core, and therefore may make the excitation energy transfer from LHCI to the core more efficient than that of land plants. On the other hand, energy-transfer paths at the two side Lhca subunits are relatively conserved. These results provide a structural basis for unravelling the mechanisms of light-energy harvesting and transfer in the moss PSI–LHCI, as well as important clues on the changes of PSI–LHCI after landing.

植物分别收集光系统I和II（PSI和PSII）周围的光合I和II（LHCI和LHCII）来收集用于光合作用的光能。在绿色植物的进化过程中，苔藓处于从水生光合生物到陆生植物的进化中间位置，是第一批降落的光合生物。在这里，我们报道了由低温电子显微镜解决的苔藓小立碗藓（Pp）的PSI-LHCI超复合物的结构，分辨率为3.23Å 。我们的结构表明，四个Lhca亚基以Lhca1–Lhca5–Lhca2–Lhca3的顺序与PSI核心相关。这个数目从8个减少到10个，这是大多数绿色藻类PSI-LHCI中的亚基数目，但与陆地植物相同。虽然Pp PSI–LHCI具有与陆地植物的PSI–LHCI类似的结构，在Lhca的第二位置具有Lhca5，而不是Lhca4，并且在绿色藻类，苔藓和陆地植物之间的叶绿素排列方式中发现了一些差异PSI–LHCI。在青苔的PSI–LHCI中发现一种叶绿素PsaF–Chl 305，位于两个中间Lhca亚基与PSI核心之间的间隙区域，因此可能使激发能从LHCI传递到核心更有效比陆地植物 另一方面，在两个Lhca亚基上的能量传递路径相对保守。这些结果为揭示苔藓PSI-LHCI中光能的收集和转移的机理提供了结构基础，以及着陆后PSI-LHCI变化的重要线索。