Plant Cell Illumina
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

First published online March 20, 2009; 10.1105/tpc.109.210313

The Plant Cell 21:700

This Article
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
21/3/700    most recent
tpc.109.210313v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Related articles in Plant Cell
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Eckardt, N. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Eckardt, N. A.
Agricola
Right arrow Articles by Eckardt, N. A.

IN BRIEF

A New Chlorophyll Degradation Pathway

Nancy A. Eckardt

Senior Features Editor

neckardt{at}aspb.org

Chlorophyll degradation is vital during leaf senescence and fruit ripening, as it allows for recycling of nitrogen and other nutrients and for protection from buildup of phototoxic chlorophyll intermediates (Hörtensteiner, 2006Go). The first steps in chlorophyll breakdown are the removal of the phytol tail (dephytylation) and the central Mg atom. It has been thought that dephytylation typically occurs first, catalyzed by the enzyme chlorophyllase, which converts chlorophyll to phytol and chlorophyllide. Removal of Mg subsequently converts chlorophyllide to pheophorbide. However, Arabidopsis contains just two known chlorophyllases, CHL1 and CHL2, and it has been shown that neither of these isoforms is localized to plastids, and double knockout mutant plants still are able to degrade chlorophyll during leaf senescence (Schenk et al., 2007Go). Now, Schelbert et al. (pages 767–785) report the discovery of a novel plastid-localized enzyme, pheophytinase, that is essential for chlorophyll breakdown during leaf senescence.

Based on the results of Schenk et al. (2007)Go, Schelbert et al. set out to discover the true chlorophyllase that functions during leaf senescence, using a combination of bioinformatics and reverse genetics. They reasoned that the protein should contain an {alpha}/β hydrolase fold characteristic of enzymes that catalyze an ester hydrolysis. Of 462 such proteins found in the Arabidopsis genome, the search was narrowed to 30 with predicted localization in chloroplasts and no previously defined function, and just three of these corresponded to genes that showed a leaf senescence-related pattern of expression. T-DNA insertion mutants of these genes were obtained, and one of these mutants showed a stay-green phenotype, indicating a lesion in chlorophyll breakdown during leaf senescence (see figure ). The authors show that the corresponding enzyme is a pheophytinase (PPH), which specifically dephytylates the Mg-free chlorophyll pigment pheophytin and does not act on chlorophyll. They also found that putative PPH orthologs are common in eukaryotic photosynthesizing organisms, suggesting that the pathway may be highly conserved.


Figure 1
View larger version (32K):
[in this window]
[in a new window]
[as a PowerPoint slide]
  		Deficiency of PPH causes a stay-green phenotype. Leaves after 5 d of dark-induced senescence are shown, left to right: wild type (Col-0), pph-1 mutant, complementation of the stay-green phenotype of pph-1 with a 35S-PPH cDNA construct, and lack of complementation using a construct harboring a mutation of the proposed active-site Ser residue (35S-PPHS221A). (Image from Figure 2 of Schelbert et al. [2009]Go.)

 
This work indicates that the previously accepted pathway of chlorophyll degradation must be revised. During leaf senescence, removal of Mg to form pheophytin is likely the first step, followed by removal of the phytol tail, catalyzed by PPH. Chlorophyllide, which is the last precursor of chlorophyll biosynthesis, is most likely not an intermediate of breakdown. Therefore, chlorophyll synthesis and breakdown are metabolically separated during leaf senescence. Based on patterns of expression, chlorophyllase may play a role in chlorophyll breakdown during fruit ripening (Azoulay Shemer et al., 2008Go) and response to pathogens and wounding (Kariola et al., 2005Go).

Footnotes

www.plantcell.org/cgi/doi/10.1105/tpc.109.210313

REFERENCES

Azoulay Shemer, T., Harpaz-Saad, S., Belausov, E., Lovat, N., Krokhin, O., Spicer, V., Standing, K.G., Goldschmidt, E.E., and Eyal, Y. (2008). Citrus chlorophyllase dynamics at ethylene-induced fruit color-break: A study of chlorophyllase expression, post-translational processing kinetics and in-situ intracellular localization. Plant Physiol. 148: 108–118.[Abstract/Free Full Text]

Hörtensteiner, S. (2006). Chlorophyll degradation during senescence. Annu. Rev. Plant Biol. 57: 55–77.[CrossRef][Medline]

Kariola, T., Brader, G., Li, J., and Palva, E.T. (2005). Chlorophyllase 1, a damage control enzyme, affects the balance between defense pathways in plants. Plant Cell 17: 282–294.[Abstract/Free Full Text]

Schelbert, S., Aubry, S., Burla, B., Agne, B., Kessler, F., Krupinska, K., and Hörtensteiner, S. (2009). Pheophytin pheophorbide hydrolase (pheophytinase) is involved in chlorophyll breakdown during leaf senescence in Arabidopsis. Plant Cell 21: 767–785.[Abstract/Free Full Text]

Schenk, N., Schelbert, S., Kanwischer, M., Goldschmidt, E.E., Dörmann, P., and Hörtensteiner, S. (2007). The chlorophyllases AtCLH1 and AtCLH2 are not essential for senescence-related chlorophyll breakdown in Arabidopsis thaliana. FEBS Lett. 581: 5517–5525.[CrossRef][Web of Science][Medline]


Related articles in Plant Cell:

Pheophytin Pheophorbide Hydrolase (Pheophytinase) Is Involved in Chlorophyll Breakdown during Leaf Senescence in Arabidopsis
Silvia Schelbert, Sylvain Aubry, Bo Burla, Birgit Agne, Felix Kessler, Karin Krupinska, and Stefan Hörtensteiner
Plant Cell 2009 21: 767-785. [Abstract] [Full Text]  




This Article
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
21/3/700    most recent
tpc.109.210313v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Related articles in Plant Cell
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Eckardt, N. A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Eckardt, N. A.
Agricola
Right arrow Articles by Eckardt, N. A.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
ASPB Publications THE PLANT CELL PLANT PHYSIOLOGY
Copyright © 2009 by the American Society of Plant Biologists