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Antenna arrangement and energy-transfer pathways of PSI-LHCI from the moss Physcomitrella patens.

ABSTRACT: 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.

SUBMITTER: Yan Q

PROVIDER: S-EPMC7884438 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature

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Antenna arrangement and energy-transfer pathways of PSI-LHCI from the moss Physcomitrella patens.

Yan Qiujing Q Zhao Liang L Wang Wenda W Pi Xiong X Han Guangye G Wang Jie J Cheng Lingpeng L He Yi-Kun YK Kuang Tingyun T Qin Xiaochun X Sui Sen-Fang SF Shen Jian-Ren JR

Cell discovery 20210216 1

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 ...[more]

PMID: 33589616

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Project description:BACKGROUND: Hexokinase catalyzes the phosphorylation of glucose and fructose, but it is also involved in sugar sensing in both fungi and plants. We have previously described two types of hexokinases in the moss Physcomitrella. Type A, exemplified by PpHxk1, the major hexokinase in Physcomitrella, is a soluble protein that localizes to the chloroplast stroma. Type B, exemplified by PpHxk2, has an N-terminal membrane anchor. Both types are found also in vascular plants, and localize to the chloroplast stroma and mitochondrial membranes, respectively. RESULTS: We have now characterized all 11 hexokinase encoding genes in Physcomitrella. Based on their N-terminal sequences and intracellular localizations, three of the encoded proteins are type A hexokinases and four are type B hexokinases. One of the type B hexokinases has a splice variant without a membrane anchor, that localizes to the cytosol and the nucleus. However, we also found two new types of hexokinases with no obvious orthologs in vascular plants. Type C, encoded by a single gene, has neither transit peptide nor membrane anchor, and is found in the cytosol and in the nucleus. Type D hexokinases, encoded by three genes, have membrane anchors and localize to mitochondrial membranes, but their sequences differ from those of the type B hexokinases. Interestingly, all moss hexokinases are more similar to each other in overall sequence than to hexokinases from other plants, even though characteristic sequence motifs such as the membrane anchor of the type B hexokinases are highly conserved between moss and vascular plants, indicating a common origin for hexokinases of the same type. CONCLUSIONS: We conclude that the hexokinase gene family is more diverse in Physcomitrella, encoding two additional types of hexokinases that are absent in vascular plants. In particular, the presence of a cytosolic and nuclear hexokinase (type C) sets Physcomitrella apart from vascular plants, and instead resembles yeast, where all hexokinases localize to the cytosol. The fact that all moss hexokinases are more similar to each other than to hexokinases from vascular plants, even though both type A and type B hexokinases are present in all plants, further suggests that the hexokinase gene family in Physcomitrella has undergone concerted evolution.

Dataset Information

Antenna arrangement and energy-transfer pathways of PSI-LHCI from the moss Physcomitrella patens.

Publications

Antenna arrangement and energy-transfer pathways of PSI-LHCI from the moss Physcomitrella patens.

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