Genome-wide transcriptome analysis of gametophyte development in Physcomitrella patens

<p>Abstract</p> <p>Background</p> <p>Regulation of gene expression plays a pivotal role in controlling the development of multicellular plants. To explore the molecular mechanism of plant developmental-stage transition and cell-fate determination, a genome-wide analysis was undertaken of sequential developmental time-points and individual tissue types in the model moss <it>Physcomitrella patens </it>because of the short life cycle and relative structural simplicity of this plant.</p> <p>Results</p> <p>Gene expression was analyzed by digital gene expression tag profiling of samples taken from <it>P. patens </it>protonema at 3, 14 and 24 days, and from leafy shoot tissues at 30 days, after protoplast isolation, and from 14-day-old caulonemal and chloronemal tissues. In total, 4333 genes were identified as differentially displayed. Among these genes, 4129 were developmental-stage specific and 423 were preferentially expressed in either chloronemal or caulonemal tissues. Most of the differentially displayed genes were assigned to functions in organic substance and energy metabolism or macromolecule biosynthetic and catabolic processes based on gene ontology descriptions. In addition, some regulatory genes identified as candidates might be involved in controlling the developmental-stage transition and cell differentiation, namely MYB-like, HB-8, AL3, zinc finger family proteins, bHLH superfamily, GATA superfamily, GATA and bZIP transcription factors, protein kinases, genes related to protein/amino acid methylation, and auxin, ethylene, and cytokinin signaling pathways.</p> <p>Conclusions</p> <p>These genes that show highly dynamic changes in expression during development in <it>P. patens </it>are potential targets for further functional characterization and evolutionary developmental biology studies.</p

Structure and energy transfer pathways of the plant photosystem I-LHCI supercomplex

Photosystem I (PSI) is one of the two photosystems in oxygenic photosynthesis, and absorbs light energy to generate reducing power for the reduction of NADP+ to NADPH with a quantum efficiency close to 100%. The plant PSI core forms a supercomplex with light-harvesting complex I (LHCI) with a total molecular weight of over 600 kDa. Recent X-ray structure analysis of the PSI-LHCI membrane-protein supercomplex has revealed detailed arrangement of the light-harvesting pigments and other cofactors especially within LHCI. Here we introduce the overall structure of the PSI-LHCI supercomplex, and then focus on the excited energy transfer (EET) pathways from LHCI to the PSI core and photoprotection mechanisms based on the structure obtained

No Detectable Maternal Effects of Elevated CO2 on Arabidopsis thaliana Over 15 Generations

Maternal environment has been demonstrated to produce considerable impact on offspring growth. However, few studies have been carried out to investigate multi-generational maternal effects of elevated CO2 on plant growth and development. Here we present the first report on the responses of plant reproductive, photosynthetic, and cellular characteristics to elevated CO2 over 15 generations using Arabidopsis thaliana as a model system. We found that within an individual generation, elevated CO2 significantly advanced plant flowering, increased photosynthetic rate, increased the size and number of starch grains per chloroplast, reduced stomatal density, stomatal conductance, and transpiration rate, and resulted in a higher reproductive mass. Elevated CO2 did not significantly influence silique length and number of seeds per silique. Across 15 generations grown at elevated CO2 concentrations, however, there were no significant differences in these traits. In addition, a reciprocal sowing experiment demonstrated that elevated CO2 did not produce detectable maternal effects on the offspring after fifteen generations. Taken together, these results suggested that the maternal effects of elevated CO2 failed to extend to the offspring due to the potential lack of genetic variation for CO2 responsiveness, and future plants may not evolve specific adaptations to elevated CO2 concentrations

Structure of photosystem I-LHCI-LHCII from the green alga Chlamydomonas reinhardtii in State 2

Photosystem I (PSI) and II (PSII) balance their light energy distribution absorbed by their light-harvesting complexes (LHCs) through state transition to maintain the maximum photosynthetic performance and to avoid photodamage. In state 2, a part of LHCII moves to PSI, forming a PSI-LHCI-LHCII supercomplex. The green alga Chlamydomonas reinhardtii exhibits state transition to a far larger extent than higher plants. Here we report the cryo-electron microscopy structure of a PSI-LHCI-LHCII supercomplex in state 2 from C. reinhardtii at 3.42 Å resolution. The result reveals that the PSI-LHCI-LHCII of C. reinhardtii binds two LHCII trimers in addition to ten LHCI subunits. The PSI core subunits PsaO and PsaH, which were missed or not well-resolved in previous Cr-PSI-LHCI structures, are observed. The present results reveal the organization and assembly of PSI core subunits, LHCI and LHCII, pigment arrangement, and possible pathways of energy transfer from peripheral antennae to the PSI core

Structure and distinct supramolecular organization of a PSII-ACPII dimer from a cryptophyte alga Chroomonas placoidea

Cryptophyte algae are an evolutionarily distinct and ecologically important group of photosynthetic unicellular eukaryotes. Photosystem II (PSII) of cryptophyte algae associates with alloxanthin chlorophyll a/c-binding proteins (ACPs) to act as the peripheral light-harvesting system, whose supramolecular organization is unknown. Here, we purify the PSII-ACPII supercomplex from a cryptophyte alga Chroomonas placoidea (C. placoidea), and analyze its structure at a resolution of 2.47 & Aring; using cryo-electron microscopy. This structure reveals a dimeric organization of PSII-ACPII containing two PSII core monomers flanked by six symmetrically arranged ACPII subunits. The PSII core is conserved whereas the organization of ACPII subunits exhibits a distinct pattern, different from those observed so far in PSII of other algae and higher plants. Furthermore, we find a Chl a-binding antenna subunit, CCPII-S, which mediates interaction of ACPII with the PSII core. These results provide a structural basis for the assembly of antennas within the supercomplex and possible excitation energy transfer pathways in cryptophyte algal PSII, shedding light on the diversity of supramolecular organization of photosynthetic machinery

Structural basis for energy transfer in a huge diatom PSI-FCPI supercomplex

Diatom is an important group of marine algae and contributes to around 20% of the global photosynthetic carbon fixation. Photosystem I (PSI) of diatoms is associated with a large number of fucoxanthin-chlorophyll a/c proteins (FCPIs). We report the structure of PSI-FCPI from a diatom Chaetoceros gracilis at 2.38 Å resolution by single-particle cryo-electron microscopy. PSI-FCPI is a monomeric supercomplex consisting of 12 core and 24 antenna subunits (FCPIs), and 326 chlorophylls a, 34 chlorophylls c, 102 fucoxanthins, 35 diadinoxanthins, 18 β-carotenes and some electron transfer cofactors. Two subunits designated PsaR and PsaS were found in the core, whereas several subunits were lost. The large number of pigments constitute a unique and huge network ensuring efficient energy harvesting, transfer and dissipation. These results provide a firm structural basis for unraveling the mechanisms of light-energy harvesting, transfer and quenching in the diatom PSI-FCPI, and also important clues to evolutionary changes of PSI-LHCI

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

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 angstrom 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

LHCA4 residues surrounding red chlorophylls allow for fine-tuning of the spectral region for photosynthesis in Arabidopsis thaliana

Improving far-red light utilization could be an approach to increasing crop production under suboptimal conditions. In land plants, only a small part of far-red light can be used for photosynthesis, which is captured by the antenna proteins LHCAs of photosystem I (PSI) through the chlorophyll (Chl) pair a603 and a609. However, it is unknown how the energy level of Chls a603–a609 is fine-tuned by the local protein environment in vivo. In this study, we investigated how changing the amino acid ligand for Chl a603 in LHCA4, the most red-shifted LHCA in Arabidopsis thaliana, or one amino acid near Chl a609, affected the energy level of the resulting PSI-LHCI complexes in situ and in vitro. Substitutions of the Chl a603 ligand N99 caused a blue shift in fluorescence emission, whereas the E146Q substitution near Chl a609 expanded the emission range to the red. Purified PSI-LHCI complexes with N99 substitutions exhibited the same fluorescence emission maxima as their respective transgenic lines, while the extent of red shift in purified PSI-LHCI with the E146Q substitution was weaker than in the corresponding transgenic lines. We propose that substituting amino acids surrounding red Chls can tune their energy level higher or lower in vivo, while shifting the absorption spectrum more to the red could prove more difficult than shifting to the blue end of the spectrum. Here, we report the first in vivo exploration of changing the local protein environment on the energy level of the red Chls, providing new clues for engineering red/blue-shifted crops