Structure and Function of Cema Homologue (PXCA) in Cyanobacteria

The cemA (ycf10) gene codes for a chloroplast envelope membrane protein [1] and is conserved in higher and lower plants and in algae [2–8]. CemA in higher plants consists of 229 to 231 amino-acids [2–4] whereas that in liverwort (Marchantia) [5] and Chlamydomonas [6] is much larger and consists of 434 and 500 amino-acids, respectively. Recent sequencing of whole chloroplast genomes of Porphyra [7] and Chlorella [8] revealed that cemA in these algae encodes proteins of 278 and 264 amino-acids, respectively. The function of CemA is not known. Rolland et al [6] have constructed mutants by disrupting cemA in Chlamydomonas. They showed that the disruption of the gene led to increased light sensitivity and affected CO2-dependent photosynthesis and inorganic carbon uptake.