Analysis of an Arabidopsis heat-sensitive mutant reveals that chlorophyll synthase is involved in reutilization of chlorophyllide during chlorophyll turnover

Authors

  • Yao-Pin Lin,

    1. Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan
    2. Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan
    3. Graduate Institute of Biotechnology, National Chung-Hsing University, Taichung, Taiwan
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  • Tsung-yuan Lee,

    1. Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan
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  • Ayumi Tanaka,

    1. Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan
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  • Yee-yung Charng

    Corresponding author
    1. Agricultural Biotechnology Research Center, Academia Sinica, Taipei, Taiwan
    2. Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan
    3. Biotechnology Center, National Chung-Hsing University, Taichung, Taiwan
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Summary

Chlorophylls, the most abundant pigments in the photosynthetic apparatus, are constantly turned over as a result of the degradation and replacement of the damage-prone reaction center D1 protein of photosystem II. Results from isotope labeling experiments suggest that chlorophylls are recycled by reutilization of chlorophyllide and phytol, but the underlying mechanism is unclear. In this study, by characterization of a heat-sensitive Arabidopsis mutant we provide evidence of a salvage pathway for chlorophyllide a. A missense mutation in CHLOROPHYLL SYNTHASE (CHLG) was identified and confirmed to be responsible for a light-dependent, heat-induced cotyledon bleaching phenotype. Following heat treatment, mutant (chlg-1) but not wild-type seedlings accumulated a substantial level of chlorophyllide a, which resulted in a surge of phototoxic singlet oxygen. Immunoblot analysis suggested that the mutation destabilized the chlorophyll synthase proteins and caused a conditional blockage of esterification of chlorophyllide a after heat stress. Accumulation of chlorophyllide a after heat treatment occurred during recovery in the dark in the light-grown but not the etiolated seedlings, suggesting that the accumulated chlorophyllides were not derived from de novo biosynthesis but from de-esterification of the existing chlorophylls. Further analysis of the triple mutant harboring the CHLG mutant allele and null mutations of CHLOROPHYLLASE1 (CLH1) and CLH2 indicated that the known chlorophyllases are not responsible for the accumulation of chlorophyllide a in chlg-1. Taken together, our results show that chlorophyll synthase acts in a salvage pathway for chlorophyll biosynthesis by re-esterifying the chlorophyllide a produced during chlorophyll turnover.

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