Humboldt-Universität zu Berlin - AG Pflanzenphysiologie

Analysis of proteins affecting MgProtoME cyclase activity

Josephine Herbst, Annabel Girke

 

One of the least understood reactions in the tetrapyrrole biosynthesis pathway is the formation of the fifth isocyclic ring of chlorins leading to the conversion from Mg protoporphyrin IX- monomethylester (MgProtoME) to protochlorophyllide. This reaction is catalyzed by the CHL27 protein, which is the essential subunit of the cyclase complex. Inducible chl27 knockout lines in A. thaliana showed a severe photosensitized, chlorotic phenotype, due to the strong accumulation of intermediates.

In addition to the CHL27 protein, the HYPOTHETICAL CHLOROPLAST OPEN-READING FRAME 54 (YCF54; LOW CHLOROPHYLL-A ACCUMULATION, LCAA) was found to be an important proteint of the cyclase complex. Investigations of YCF54 overexpression (OEX) and co-suppression (CoS) in A. thaliana, as well as other in planta studies, highlight the interaction between CHL27 and YCF54 (Figure below). Pull down experiments contributed to identify further potential interaction partners, which will currently be explored for their regulatory roles in the cyclase complex and the overall chlorophyll biosynthesis.

 

Unpublished results provided by J. Herbst A: Phenotype of Arabidopsis thaliana transgenic line with overproduction or inactivated synthesis of YCF54. B: Overproduction and lack of YCF54 compromised the CHL27 content. C: Modified steadystate levels of MgProtoME and PChlide in YCFOE or COS line in comparison to wild type control.
Abb.: Unpublished results provided by Josephine Herbst

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A: Phenotype of Arabidopsis thaliana transgenic line with overproduction or inactivated synthesis of YCF54.
B: Overproduction and lack of YCF54 compromised the CHL27 content.
C: Modified steadystate levels of MgProtoME and PChlide in YCFOE or COS line in comparison to wild type control.

 

YCF54 co-suppression (CoS) lines show a pale green phenotype in comparison to a wild-type seedling (A). The loss in chlorophyll content correlates with a strong decrease of YCF54 and CHL27 content (B), which causes an accumulation of MgProtoME (C). In comparison to the CoS lines, YCF54-overexpressor (OEX) lines show a wild-type like phenotype (A). The amounts of YCF54 and CHL27 are upregulated (B), which lead to an accumulation of the phototoxic protochlorophyllide (PChilde; C). Experiments and figures prepared by Josephine Herbst.