Metabolic changes and physiological responses induced by space ionizing radiation in Chlamydomonas reinhardtii D1 mutants
Author(s)
Pastorelli, Sandro
Date Issued
March 16, 2012
Type
Doctoral Thesis
Abstract
This research aimed to select, isolate and characterize different algal phenotypes of the genus
Chlamydomonas, tolerant to ionizing radiation and radical-inducing conditions, to be used as life
regenerative supporting systems in long-term space mission. The photosynthetic apparatus evolved
several molecular mechanisms to overcome oxidative stress. D1 aminoacids close to the oxygen
evolving complex in particular to Tyr161, play an essential role in the maintenance of
photosynthetic electron transport and often are the target of free radical-induced damage. In vitro
directed evolution strategies targeted at the D1 protein were adopted to create libraries of
Chlamydomonas random mutants further selected by exposures to proton or neutron sources.
Chlamydomonas reinhardtii strains wild type and mutated in both the D1 protein and some
carotenogenic genes were sent to space in the Foton-M3 space mission (ESA, 2007).
Moreover, site directed D1 mutants were tested for their capability to cope with free radical
generating conditions on ground. Based on these results the site directed mutants I163N, I163T and
P162S were enclosed in the PHOTO I experiment unit and experienced the ISS environment during
the STS-134 mission as BIOKIS-PHOTOEVOLUTION, one of the experiments developed into the
frame of the DAMA project (NASA, 2011). After the flights, different mutants displayed a higher
photosynthetic performance compared to their reference strains followed by metabolic changes as
gene expression, antioxidant pigments accumulation and modified electron transport. This study
confirmed that single D1 aminoacidic substitutions close to Tyr161 are important to efficiently
counteract the extreme space environment, encouraging the development of innovative
photosynthesis-based life regenerative supporting systems for long-term space missions.
Additional information
Dottorato di ricerca in Biotecnologie vegetali
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