Research article

Complementation of a phycocyanin-bilin lyase from Synechocystis sp. PCC 6803 with a nucleomorph-encoded open reading frame from the cryptophyte Guillardia theta

Kathrin Bolte^{* 1} , Oliver Kawach^{* 1} , Julia Prechtl^{* 1} , Nicole Gruenheit² , Julius Nyalwidhe³ and Uwe-G Maier¹

¹Philipps-Universität Marburg, Laboratorium für Zellbiologie, Karl-von-Frisch Str., D-35032 Marburg, Germany

²Heinrich-Heine Universität Düsseldorf, Institut für Botanik III, Universitätsstr. 1, D-40225 Düsseldorf, Germany

³Philipps-Universität Marburg, Laboratorium für Parasitologie, Karl-von-Frisch Str., D-35032 Marburg, Germany

author email corresponding author email* Contributed equally

BMC Plant Biology 2008, 8:56doi:10.1186/1471-2229-8-56

Published:	16 May 2008

Abstract

Background

Cryptophytes are highly compartmentalized organisms, expressing a secondary minimized eukaryotic genome in the nucleomorph and its surrounding remnant cytoplasm, in addition to the cell nucleus, the mitochondrion and the plastid. Because the members of the nucleomorph-encoded proteome may contribute to essential cellular pathways, elucidating nucleomorph-encoded functions is of utmost interest. Unfortunately, cryptophytes are inaccessible for genetic transformations thus far. Therefore the functions of nucleomorph-encoded proteins must be elucidated indirectly by application of methods in genetically accessible organisms.

Results

Orf222, one of the uncharacterized nucleomorph-specific open reading frames of the cryptophyte Guillardia theta, shows homology to slr1649 of Synechocystis sp. PCC 6803. Recently a further homolog from Synechococcus sp. PCC 7002 was characterized to encode a phycocyanin-β155-bilin lyase. Here we show by insertion mutagenesis that the Synechocystis sp. PCC 6803 slr1649-encoded protein also acts as a bilin lyase, and additionally contributes to linker attachment and/or stability of phycobilisomes. Finally, our results indicate that the phycocyanin-β155-bilin lyase of Synechocystis sp. PCC 6803 can be complemented in vivo by the nucleomorph-encoded open reading frame orf222.

Conclusion

Our data show that the loss of phycocyanin-lyase function causes pleiotropic effects in Synechocystis sp. PCC 6803 and indicate that after separating from a common ancestor protein, the phycoerythrin lyase from Guillardia theta has retained its capacity to couple a bilin group to other phycobiliproteins. This is a further, unexpected example of the universality of phycobiliprotein lyases.