Biology subjects

Guardini, Z.

Publications and source records attributed to Guardini, Z..

3 recordsLinked to original sources

bioRxiv2025

Structural determinants for red-shifted absorption in higher-plants Photosystem I

- Higher plants Photosystem I absorbs near-infrared light through long-wavelength chlorophylls, enriched under vegetation canopies, to enhance photon capture. Far-red absorption originates from chlorophylls pairs within the Lhca3 and Lhca4 subunits of the LHCI antenna, known as the "red cluster" composed of chlorophylls a603 and a609. - We used reverse genetics to produce an Arabidopsis mutant devoid of red-shifted absorption, and we obtained high-resolution cryo-EM structures from purified PSI-LHCI complexes in both wild-type and mutant plants. - Computed excitonic coupling values suggested a possible contribution of additional nearby pigment molecules, namely chlorophyll a615 and violaxanthin in L2 site, to far-red absorption. Therefore, we investigated the structural determinants of far-red absorption and analyzed the spectroscopic effects of these additional pigments by producing further Arabidopsis transgenic lines. The two experimental structures were used for quantum mechanics calculations, revealing that excitonic interactions alone cannot explain far-red absorption, while charge transfer states were needed for accurate spectral simulations. - Our findings demonstrate that the molecular mechanisms of light-harvesting under shaded conditions rely on very precise tuning of chromophore interactions, an understanding of which is crucial for designing light-harvesting complexes with engineered absorption spectra

plant biology↗

bioRxiv2025

The minor antennae of photosystem II contribute to qH-energy dissipation in Arabidopsis

Photosynthesis is a biological process that converts light energy into chemical energy. Excessive light can damage the photosynthetic machinery, so plants have evolved photoprotective mechanisms such as non-photochemical quenching (NPQ). Among the NPQ mechanisms, qH is a form of sustained quenching, dependent on LIPOCALIN IN THE PLASTID (LCNP) and repressed by SUPPRESSOR OF QUENCHING 1 (SOQ1), protecting against abiotic stress. Recently, we showed in Arabidopsis thaliana that qH can occur in the major light-harvesting complexes (Lhcb1, Lhcb2, Lhcb3) but independently of any specific major antenna. Interestingly, in mutants with little or no accumulation of major antennae (koLHCII, lhcb1, cpsrp43), qH can still be induced. Here, we show that the minor antennae can be quenched by qH and remain quenched once isolated. To investigate the role of minor antennae in qH, we combined the soq1 mutant, which displays high qH, with mutations in each minor antenna type (Lhcb4, Lhcb5, or Lhcb6), or with a mutant lacking all minor antennae. None are strictly required for qH to occur. Still, the absence of Lhcb6 decreases qH induction likely due to an indirect effect from the slower electron transport rate and/or a different macro-organization of photosynthetic complexes in the thylakoids. Overall, this work demonstrates that the minor antennae are a secondary target for qH and could serve as an additional safety valve for photoprotective energy dissipation during prolonged stress.

plant biology↗

bioRxiv2022

Thylakoid grana stacking revealed by multiplex genome editing of LHCII encoding genes

Land plant chloroplasts differ from algal ones for their thylakoid membranes being organized in grana: piles of vesicles paired by their stromal surface, forming domains including Photosystem (PS) II and its antenna while excluding PS I and ATPase to stroma membranes, connecting grana stacks. The molecular basis of grana stacking remain unclear. We obtained genotypes lacking the trimeric antenna complex (Lhcb1-2-3), the monomeric Lhcb4-5-6, or both. Full deletion caused loss of grana, while either monomers or trimers support 50% stacking. The expression of Lhcb5 alone restored stacking at 50%, while Lhcb2 alone produced huge grana which broke down upon light exposure. Cyclic electron transport was maintained in the lack of stacking, while excitation energy balance between photosystems and the repair efficiency of damaged Photosystem II were affected. We conclude that grana evolved for need of regulating energy balance between photosystems under terrestrial canopy involving rapid changes in photon spectral distribution.

plant biology↗