title: An easily reversible structural change underlies mechanisms enabling desert crust cyanobacteria to survive desiccation.
abstract: Biological desert sand crusts are the foundation of desert ecosystems, stabilizing the sands and allowing colonization by higher order organisms. The first colonizers of the desert sands are cyanobacteria. Facing the harsh conditions of the desert, these organisms must withstand frequent desiccation-hydration cycles, combined with high light intensities. Here, we characterize structural and functional modifications to the photosynthetic apparatus that enable a cyanobacterium, Leptolyngbya sp., to thrive under these conditions. Using multiple in vivo spectroscopic and imaging techniques, we identified two complementary mechanisms for dissipating absorbed energy in the desiccated state. The first mechanism involves the reorganization of the phycobilisome antenna system, increasing excitonic coupling between antenna components. This provides better energy dissipation in the antenna rather than directed exciton transfer to the reaction center. The second mechanism is driven by constriction of the thylakoid lumen which limits diffusion of plastocyanin to P700. The accumulation of P700(+) not only prevents light-induced charge separation but also efficiently quenches excitation energy. These protection mechanisms employ existing components of the photosynthetic apparatus, forming two distinct functional modes. Small changes in the structure of the thylakoid membranes are sufficient for quenching of all absorbed energy in the desiccated state, protecting the photosynthetic apparatus from photoinhibitory damage. These changes can be easily reversed upon rehydration, returning the system to its high photosynthetic quantum efficiency.
authors.affiliation: Department of Plant & Environmental Sciences, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Israel.
authors.forename: Leeat
authors.initials: L
authors.lastname: Bar-Eyal
authors.affiliation: Applied Physics Department and The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Israel.
authors.forename: Ido
authors.initials: I
authors.lastname: Eisenberg
authors.affiliation: Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Israel.
authors.forename: Adam
authors.initials: A
authors.lastname: Faust
authors.affiliation: Department of Plant & Environmental Sciences, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Israel.
authors.forename: Hagai
authors.initials: H
authors.lastname: Raanan
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Reinat
authors.initials: R
authors.lastname: Nevo
authors.affiliation: UMR 7141, C.N.R.S.-UPMC, Institut de Biologie Physico-Chimique, Paris, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rappaport
authors.affiliation: Commissariat à l'Energie Atomique, Institut de Biologie et Technologies de Saclay, 91191 Gif sur Yvette, France.
authors.forename: Anja
authors.initials: A
authors.lastname: Krieger-Liszkay
authors.affiliation: Commissariat à l'Energie Atomique, Institut de Biologie et Technologies de Saclay, 91191 Gif sur Yvette, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Sétif
authors.affiliation: Commissariat à l'Energie Atomique, Institut de Biologie et Technologies de Saclay, 91191 Gif sur Yvette, France.
authors.forename: Adrien
authors.initials: A
authors.lastname: Thurotte
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Ziv
authors.initials: Z
authors.lastname: Reich
authors.affiliation: Department of Plant & Environmental Sciences, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Israel.
authors.forename: Aaron
authors.initials: A
authors.lastname: Kaplan
authors.affiliation: Department of Plant & Environmental Sciences, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Israel.
authors.forename: Itzhak
authors.initials: I
authors.lastname: Ohad
authors.affiliation: Applied Physics Department and The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Israel.
authors.forename: Yossi
authors.initials: Y
authors.lastname: Paltiel
authors.affiliation: Department of Plant & Environmental Sciences, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Israel. Electronic address: Nir.ke@mail.huji.ac.il.
authors.forename: Nir
authors.initials: N
authors.lastname: Keren
keywords: Cyanobacteria; Desert; Desiccation tolerance; Photosynthesis