Identification and molecular characterization of a novel Chlamydomonas reinhardtii mutant defective in chlorophyll biosynthesis

• DOI: 10.12688/f1000research.2-138.v1
• Publication Date: 2013-06-10T15:50:45Z
• Authors: Phillip B Grovens...; Darryel A Wilson; Cameron G Lennox; Katherine P Smith; Alisha A Contractor; Jonathan L Mincey; Kathryn D Lankford; Jacqueline M Smith; Tashana C Haye; Mautusi Mitra
• Keywords: 0301 basic medicine; 0303 health sciences; 03 medical and health sciences; Research Article

The green micro-algaChlamydomonasreinhardtiiis an elegant model organism to study all aspects of oxygenic photosynthesis. Chlorophyll (Chl) and heme are major tetrapyrroles that play an essential role in energy metabolism in photosynthetic organisms and are synthesized via a common branched tetrapyrrole biosynthetic pathway. One of the enzymes in the pathway is Mg chelatase (MgChel) which inserts Mg2+into protoporphyrin IX (PPIX, proto) to form magnesium-protoporphyrin IX (MgPPIX, Mgproto), the first biosynthetic intermediate in the Chl branch. MgChel is a multimeric enzyme that consists of three subunits designated CHLD, CHLI and CHLH. Plants have two isozymes of CHLI (CHLI1 and CHLI2) which are 70%-81% identical in protein sequences. Although the functional role of CHLI1 is well characterized, that of CHLI2 is not. We have isolated a non-photosynthetic light sensitive mutant5A7by random DNA insertional mutagenesis that is devoid of any detectable Chl. PCR based analyses show that5A7is missing theCHLI1gene and at least eight additional functionally uncharacterized genes.5A7has an intactCHLI2gene. Complementation with a functional copy of theCHLI1gene restored Chl biosynthesis, photo-autotrophic growth and light tolerance in5A7. We have identified the firstchli1mutant ofChlamydomonas reinhardtiiand in green algae. Our results show that in the wild typeChlamydomonasCHLI2 protein amount is lower than that of CHLI1 and thechli1mutant has a drastic reduction in CHLI2 protein levels although it possesses theCHLI2gene. Ourchli1mutant opens up new avenues to explore the functional roles of CHLI1 and CHLI2 in Chl biosynthesis and chloroplast to nucleus retrograde signaling inChlamydomonas,which has never been studied before.