Roberto Bassi - Academia.edu (original) (raw)

Papers by Roberto Bassi

The Plant Cell, Jun 1, 2001

We have characterized the biochemical nature and the function of PsbZ, the protein product of a u... more We have characterized the biochemical nature and the function of PsbZ, the protein product of a ubiquitous open reading frame, which is known as ycf9 in Chlamydomonas and ORF 62 in tobacco, that is present in chloroplast and cyanobacterial genomes. After raising specific antibodies to PsbZ from Chlamydomonas and tobacco, we demonstrated that it is a bona fide photosystem II (PSII) subunit. PsbZ copurifies with PSII cores in Chlamydomonas as well as in tobacco. Accordingly, PSII mutants from Chlamydomonas and tobacco are deficient in PsbZ. Using psbZ-targeted gene inactivation in tobacco and Chlamydomonas, we show that this protein controls the interaction of PSII cores with the light-harvesting antenna; in particular, PSII-LHCII supercomplexes no longer could be isolated from PsbZ-deficient tobacco plants. The content of the minor chlorophyll binding protein CP26, and to a lesser extent that of CP29, also was altered substantially under most growth conditions in the tobacco mutant and in Chlamydomonas mutant cells grown under photoautotrophic conditions. These PsbZ-dependent changes in the supramolecular organization of the PSII cores with their peripheral antennas cause two distinct phenotypes in tobacco and are accompanied by considerable modifications in (1) the pattern of protein phosphorylation within PSII units, (2) the deepoxidation of xanthophylls, and (3) the kinetics and amplitude of nonphotochemical quenching. The role of PsbZ in excitation energy dissipation within PSII is discussed in light of its proximity to CP43, in agreement with the most recent structural data on PSII.

Proceedings of the National Academy of Sciences of the United States of America, May 26, 2010

Nature plants, 2016

Author(s): Dall'Ostoa, L; Cazzanigaa, S; Bressana, M; Zigmantas, D; Palecekb, D; Zidekb, K; N... more Author(s): Dall'Ostoa, L; Cazzanigaa, S; Bressana, M; Zigmantas, D; Palecekb, D; Zidekb, K; Niyogi, KK; Fleming, GR; Bassi, R

Cell Death & Disease, 2019

Plant Physiology

Photosynthetic light-harvesting antennae are pigment-binding proteins that perform one of the mos... more Photosynthetic light-harvesting antennae are pigment-binding proteins that perform one of the most fundamental tasks on Earth, capturing light and transferring energy that enables life in our biosphere. Adaptation to different light environments led to the evolution of an astonishing diversity of light-harvesting systems. At the same time, several strategies have been developed to optimize the light energy input into photosynthetic membranes in response to fluctuating conditions. The basic feature of these prompt responses is the dynamic nature of antenna complexes, whose function readily adapts to the light available. High-resolution microscopy and spectroscopic studies on membrane dynamics demonstrate the crosstalk between antennae and other thylakoid membrane components. With the increased understanding of light-harvesting mechanisms and their regulation, efforts are focusing on the development of sustainable processes for effective conversion of sunlight into functional bio-prod...

International Conference on Ultrafast Phenomena, 2016

We present two-dimensional electronic-vibrational spectra of the chlorophyll (Chl) binding protei... more We present two-dimensional electronic-vibrational spectra of the chlorophyll (Chl) binding protein light harvesting complex II (LHCII) from spinach, and of isolated Chl a and Chl b. We show how energy transfer from Chl b to Chl a and subsequent relaxation can be directly observed in LHCII using this multidimensional technique.

Frontiers in Optics / Laser Science, 2020

We demonstrate an ultrabroadband two-dimensional electronic spectrometer that maps energy flow ac... more We demonstrate an ultrabroadband two-dimensional electronic spectrometer that maps energy flow across the visible range. This apparatus enables observation of previously unexplored carotenoid-mediated light-harvesting dynamics in plants, including identification of a debated carotenoid dark state.

Photosynthesis Research, 2007

Epj Web of Conferences, 2019

We utilise ultrabroadband two-dimensional electronic spectroscopy to map out pathways of energy f... more We utilise ultrabroadband two-dimensional electronic spectroscopy to map out pathways of energy flow in LHCII across the entire visible region. In addition to the well-established, low-lying chlorophyll Qy bands, our results reveal additional pathways of energy relaxation on the higher-lying excited states involving the S2 energy levels of carotenoids, including ultrafast carotenoid-to-chlorophyll energy transfer on 90-150 fs timescales.

Photosynthesis Research, Sep 1, 2021

Photosynthetic organisms have evolved photoprotective mechanisms to acclimate to light intensity ... more Photosynthetic organisms have evolved photoprotective mechanisms to acclimate to light intensity fluctuations in their natural growth environments. Photosystem (PS) II subunit S (PsbS) and light-harvesting complex (LHC) stress-related proteins (LhcSR) are essential for triggering photoprotection in vascular plants and green algae, respectively. The activity of both proteins is strongly enhanced in the moss Physcomitrella patens under high-light conditions. However, their role in regulating photosynthesis acclimation in P. patens under fluctuating light (FL) conditions is still unknown. Here, we compare the responses of wild-type (WT) P. patens and mutants lacking PsbS ( psbs KO) or LhcSR1 and 2 ( lhcsr KO) to FL conditions in which the low-light phases were periodically interrupted with high-light pulses. lhcsr KO mutant showed a strong reduction in growth with respect to WT and psbs KO under FL conditions. The lack of LhcSR not only decreased the level of non-photochemical quenching, resulting in an over-reduced plastoquinone pool, but also significantly increased the PSI acceptor limitation values with respect to WT and psbs KO under FL conditions. Moreover, in lhcsr KO mutant, the abundance of PSI core and PSI–LHCI complex decreased greatly under FL conditions compared with the WT and psbs KO. We proposed that LhcSR in P. patens play a crucial role in moss acclimation to dynamic light changes.

Journal of Biological Chemistry, Oct 1, 2015

Background: LHCSR protein in algae and mosses is essential for NPQ. Results: Expression and chara... more Background: LHCSR protein in algae and mosses is essential for NPQ. Results: Expression and characterization of Physcomitrella patens LHCSR1 protein upon heterologous expression in N. benthamiana and N. tabacum was obtained. Conclusion: LHCSR1 is the first member of LHC protein family lacking Chlorophyll b. It is active in NPQ. Significance: LHCSR1 isolation is crucial for the elucidation of the NPQ mechanism.

Chem, Mar 1, 2019

In green plants, carotenoids (Cars) are bound within chlorophyll-containing proteins to serve lig... more In green plants, carotenoids (Cars) are bound within chlorophyll-containing proteins to serve light-harvesting, photoprotective, and structural roles. The major light-harvesting complex of green plants (LHCII) contains four Cars, each within its own protein pocket with distinct structure and energetics. The photophysics of the Cars, including the balance of their diverse roles, remain unresolved because of the complexity of their electronic structure. We performed ultrabroadband two-dimensional electronic spectroscopy on LHCII with the spectral bandwidth and temporal resolution to map the energy transfer dynamics and electronic structure of the Cars. We found that one Car, lutein 2, provides a nexus for light harvesting, collecting energy from higher-lying states and funneling it downhill, partially via a debated dark state observed exclusively on lutein 2. These results show that the protein pocket can tune Car electronic structure via tuning the geometry, a mechanism by which plants control the photophysics of solar energy capture.

Journal of Physical Chemistry Letters, Oct 10, 2016

Light-harvesting complex II (LHCII) serves a central role in light harvesting for oxygenic photos... more Light-harvesting complex II (LHCII) serves a central role in light harvesting for oxygenic photosynthesis and is arguably the most important photosynthetic antenna complex. In this work, we present two-dimensional electronic-vibrational (2DEV) spectra of LHCII isolated from spinach, demonstrating the possibility of using this technique to track the transfer of electronic excitation energy between specific pigments within the complex. We assign the spectral bands via comparison with the 2DEV spectra of the isolated chromophores, chlorophyll a and b, and present evidence that excitation energy between the pigments of the complex are observed in these spectra. Finally, we analyze the essential components of the 2DEV spectra using singular value decomposition, which makes it possible to reveal the relaxation pathways within this complex.

This book introduces the basic physical, chemical, and biological principles underlying the first... more This book introduces the basic physical, chemical, and biological principles underlying the first steps in photosynthesis: light absorption, excitation energy transfer, and charge separation. In Part 1, we introduce pigments and their spectroscopic/ redox properties. In Part 2, pigment-proteins as they occur in various natural systems (plants, algae, photosynthetic bacteria) are described, including the regulation of light harvesting. Part 3 deals with the physics underlying light harvesting: energy transfer and electron transport. Part 4 introduces basic and advanced spectroscopic methods, including data analysis. In Part 5, we discuss artificial and natural photosynthetic systems, how they are assembled, and what the energy transfer properties are

Green plants prevent photodamage under high light conditions by dissipating excess energy as heat... more Green plants prevent photodamage under high light conditions by dissipating excess energy as heat. Conformational changes of the photosynthetic antenna complexes activate dissipation by leveraging the sensitivity of the photophysics of the chlorophyll and carotenoids to their surrounding protein. However, the mechanisms and site of dissipation are still debated, largely due to two challenges. First, experiments have been performed in detergent, which can induce non-native conformations, or in vivo, where contributions from the multiple complexes cannot be disentangled and are further obfuscated by laser-induced artifacts. Second, because of the ultrafast timescales and large energy gaps involved, measurements lacked the temporal or spectral requirements. Here, we overcome both challenges by applying ultrabroadband two-dimensional electronic spectroscopy to the principal antenna complex, light-harvesting complex II, in a near-native membrane. The spectra show that the membrane enhances two dissipative pathways, one of which was hypothesized yet previously uncharacterized. Our results suggest a resting level of dissipation that may protect against sudden solar fluctuations, and highlight that this level can even be fine-tuned by the membrane environment. File list (2) download file view on ChemRxiv MainText_052019.pdf (4.02 MiB) download file view on ChemRxiv SuppInfo.pdf (6.69 MiB)

Proceedings of the National Academy of Sciences of the United States of America, May 17, 2019

Nature Chemistry, Jul 17, 2017

In oxygenic photosynthesis, light harvesting is regulated to safely dissipate excess energy and p... more In oxygenic photosynthesis, light harvesting is regulated to safely dissipate excess energy and prevent the formation of harmful photoproducts. Regulation is known to be necessary for fitness, but the molecular mechanisms are not understood. One challenge has been that ensemble experiments average over active and dissipative behaviours, preventing identification of distinct states. Here, we use single-molecule spectroscopy to uncover the photoprotective states and dynamics of the light-harvesting complex stress-related 1 (LHCSR1) protein, which is responsible for dissipation in green algae and moss. We discover the existence of two dissipative states. We find that one of these states is activated by pH and the other by carotenoid composition, and that distinct protein dynamics regulate these states. Together, these two states enable the organism to respond to two types of intermittency in solar intensity-step changes (clouds and shadows) and ramp changes (sunrise), respectively. Our findings reveal key control mechanisms underlying photoprotective dissipation, with implications for increasing biomass yields and developing robust solar energy devices. 1 P hotosynthetic light-harvesting complexes (LHCs) capture solar 2 energy and feed it to downstream molecular machinery 1. When 3 light absorption exceeds the capacity for utilization, the excess 4 energy can generate singlet oxygen, which causes cellular damage. 5 Thus, in oxygenic photosynthesis, LHCs have evolved a feedback 6 loop that triggers photoprotective energy dissipation 2-4. The 7 crucial importance of photoprotection for fitness has been demon-8 strated, as well as its impact on biomass yields 5. Recent efforts to 9 rewire photoprotection have demonstrated an impressive 20% 10 increase in biomass 6. However, the mechanisms of photoprotec-11 tion-from the fast photophysics of the pigments to the slow con-12 formational changes of proteins-have not yet been resolved. The 13 lack of mechanistic understanding is a major limitation in the 14 speed and efficacy of improving biomass yields. 15 Collectively, the photoprotective mechanisms are known as non-16 photochemical quenching (NPQ). NPQ involves changes to the 17 photophysics, conformation and organization of LHCs within 18 the membrane 2-4. The seconds to minutes component of NPQ is 19 the dissipation of excess sunlight within the LHCs. The LHCs 20 consist of pigments (chlorophyll and carotenoids) closely packed 21 within a protein matrix. The carotenoid composition is controlled 22 by light conditions via the xanthophyll cycle, in which violaxanthin 23 (Vio) is converted to zeaxanthin (Zea) under high light conditions. 24 Most LHCs are primarily responsible for light harvesting, but in 25 recent research, one of the LHCs, light-harvesting complex stress-26 related (LHCSR) protein, was identified as the key gene product 27 for the dissipation of excess sunlight in unicellular algae and 28 mosses 7-14. LHCSR consists of chlorophyll-a and carotenoids held 29 within a protein matrix 8,12,15. Activation of dissipation in LHCSR 30 occurs based on three functional parameters: (1) low pH 8,16-18 ,

Journal of the American Chemical Society, Oct 14, 2021

Plant Physiology, Feb 1, 2003

The expression of several barley (Hordeum vulgare) cold-regulated (cor) genes during cold acclima... more The expression of several barley (Hordeum vulgare) cold-regulated (cor) genes during cold acclimation was blocked in the albino mutant a n , implying a chloroplast control on mRNAs accumulation. By using albino and xantha mutants ordered according to the step in chloroplast biogenesis affected, we show that the cold-dependent accumulation of cor14b, tmc-ap3, and blt14 mRNAs depends on plastid developmental stage. Plants acquire the ability to fully express cor genes only after the development of primary thylakoid membranes in their chloroplasts. To investigate the chloroplast-dependent mechanism involved in cor gene expression, the activity of a 643-bp cor14b promoter fragment was assayed in wild-type and albino mutant a n leaf explants using transient ␤-glucuronidase reporter expression assay. Deletion analysis identified a 27-bp region between nucleotides Ϫ274 and Ϫ247 with respect to the transcription start point, encompassing a boundary of some element that contributes to the cold-induced expression of cor14b. However, cor14b promoter was equally active in green and in albino a n leaves, suggesting that chloroplast controls cor14b expression by posttranscriptional mechanisms. Barley mutants lacking either photosystem I or II reaction center complexes were then used to evaluate the effects of redox state of electron transport chain components on COR14b accumulation. In the mutants analyzed, the amount of COR14b protein, but not the steady-state level of the corresponding mRNA, was dependent on the redox state of the electron transport chain. Treatments of the vir-zb63 mutant with electron transport chain inhibitors showed that oxidized plastoquinone promotes COR14b accumulation, thus suggesting a molecular relationship between plastoquinone/plastoquinol pool and COR14b.