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Microbial rhodopsins on leaf surfaces of terrestrial plants

Faculty of Biology, Lorry I Lokey Interdisciplinary Center for Life Sciences and Engineering, Faculty of Computer Science, Technion - Israel Institute of Technology, Haifa 32000, Israel.
Environmental Microbiology (Impact Factor: 6.24). 09/2011; 14(1):140-6. DOI: 10.1111/j.1462-2920.2011.02554.x
Source: PubMed

ABSTRACT The above-ground surfaces of terrestrial plants, the phyllosphere, comprise the main interface between the terrestrial biosphere and solar radiation. It is estimated to host up to 10(26) microbial cells that may intercept part of the photon flux impinging on the leaves. Based on 454-pyrosequencing-generated metagenome data, we report on the existence of diverse microbial rhodopsins in five distinct phyllospheres from tamarisk (Tamarix nilotica), soybean (Glycine max), Arabidopsis (Arabidopsis thaliana), clover (Trifolium repens) and rice (Oryza sativa). Our findings, for the first time describing microbial rhodopsins from non-aquatic habitats, point towards the potential coexistence of microbial rhodopsin-based phototrophy and plant chlorophyll-based photosynthesis, with the different pigments absorbing non-overlapping fractions of the light spectrum.

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    • "Microbial epiphytes, able to thrive on the leaf surface, have evolved different adaptations to cope with these extreme conditions. A phototrophic lifestyle on the leaf surface has been suggested based on the identification of microbial rhodopsins (Atamna-Ismaeel et al., 2011; Vorholt, 2012). Some of these proteins could act as proton pumps, providing additional energy to diverse members of the phylosphere. "
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    • "Furthermore, the viral sequences contained the invariant lysine residue that is involved in retinal binding as well as the aspartic acid that serves as the proton acceptor; the proton donor glutamate is not conserved; the position known to be important for spectral tuning [17] is occupied by a methionine as it is in some of the proteorhodopsins (Figure  1). The lack of conservation of the proton donor carboxylate indicate that viral proteorhodopsin homologs are sensory rhodopsins rather than light-dependent proton pumps [18,19]. The presence of a hydrophobic residue in the spectral tuning position suggests that viral proteorhodopsins absorb light in the green part of the spectrum [17]. "
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