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Different mechanisms are responsible for chlorophyll dephytylation during fruit ripening and leaf senescence in tomato.

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Guyer Luzia, Hofstetter Silvia Schelbert, Christ Bastien, Lira Bruno Silvestre, Rossi Magdalena, Hörtensteiner Stefan,
Project Chlorophyll breakdown: catabolite modification and transport, and the relation to stoma function and cell death signalling
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Original article (peer-reviewed)

Journal Plant physiology
Volume (Issue) 166(1)
Page(s) 44 - 56
Title of proceedings Plant physiology
DOI 10.1104/pp.114.239541

Open Access

URL http://www.plantphysiol.org/content/166/1/44
Type of Open Access Publisher (Gold Open Access)

Abstract

Chlorophyll breakdown occurs in different green plant tissues (e.g. during leaf senescence and in ripening fruits). For different plant species, the PHEOPHORBIDE A OXYGENASE (PAO)/phyllobilin pathway has been described to be the major chlorophyll catabolic pathway. In this pathway, pheophorbide (i.e. magnesium- and phytol-free chlorophyll) occurs as a core intermediate. Most of the enzymes involved in the PAO/phyllobilin pathway are known; however, the mechanism of dephytylation remains uncertain. During Arabidopsis (Arabidopsis thaliana) leaf senescence, phytol hydrolysis is catalyzed by PHEOPHYTINASE (PPH), which is specific for pheophytin (i.e. magnesium-free chlorophyll). By contrast, in fruits of different Citrus spp., chlorophyllase, hydrolyzing phytol from chlorophyll, was shown to be active. Here, we enlighten the process of chlorophyll breakdown in tomato (Solanum lycopersicum), both in leaves and fruits. We demonstrate the activity of the PAO/phyllobilin pathway and identify tomato PPH (SlPPH), which, like its Arabidopsis ortholog, was specifically active on pheophytin. SlPPH localized to chloroplasts and was transcriptionally up-regulated during leaf senescence and fruit ripening. SlPPH-silencing tomato lines were impaired in chlorophyll breakdown and accumulated pheophytin during leaf senescence. However, although pheophytin transiently accumulated in ripening fruits of SlPPH-silencing lines, ultimately these fruits were able to degrade chlorophyll like the wild type. We conclude that PPH is the core phytol-hydrolytic enzyme during leaf senescence in different plant species; however, fruit ripening involves other hydrolases, which are active in parallel to PPH or are the core hydrolases in fruits. These hydrolases remain unidentified, and we discuss the question of whether chlorophyllases might be involved.
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