Disruption of the plastid ycf10 open reading frame affects uptake of inorganic carbon in the chloroplast of Chlamydomonas

Abstract

The product of the chloroplast ycf10 gene has been localized in the inner chloroplast envelope membrane (Sasaki et al., 1993) and found to display sequence homology with the cyanobacterial CotA product which is altered in mutants defective in CO 2 transport and proton extrusion (Katoh et al., 1996a,b). In Chlamydomonas reinhardtii, ycf10, located between the psbI and atpH genes, encodes a putative hydrophobic protein of 500 residues, which is considerably larger than its higher plant homologue because of a long insertion that separates the conserved N and C termini. Using biolistic transformation, we have disrupted ycf10 with the chloroplast aadA expression cassette and examined the phenotype of the homoplasmic transformants. These were found to grow both photoheterotrophically and photoautotrophically under low light, thereby revealing that the Ycf10 product is not essential for the photosynthetic reactions. However, under high light these transformants did not grow photoautotrophically and barely photoheterotrophically. The increased light sensitivity of the transformants appears to result from a limitation in photochemical energy utilization and/or dissipation which correlates with a greatly diminished photosynthetic response to exogenous (CO 2 ⍣ HCO 3 -), especially under conditions where the chloroplast inorganic carbon transport system is not induced. Mass spectrometric measurements with either whole cells or isolated chloroplasts from the transformants revealed that the CO 2 and HCO 3 -uptake systems have a reduced affinity for their substrates. The results suggest the existence of a ycf10-dependent system within the plastid envelope which promotes efficient inorganic carbon (Ci) uptake into chloroplasts.

Thylakoid Lumen Carbonic Anhydrase (CAH3) Mutation Suppresses Air-Dier Phenotype of LCIB Mutant in Chlamydomonas reinhardtii

“…Although the products of several limiting-CO 2 -inducible genes have been identified as putative Ci transporters on the chloroplast envelope, including LCIA, LCI1, CCP1/2, and Ycf10, or on the plasma membrane, including HLA3, none of the respective gene products have been definitively determined to transport Ci species (Burow et al, 1996;Chen et al, 1997;Rolland et al, 1997;Im and Grossman, 2001;Miura et al, 2004;Pollock et al, 2004;Mariscal et al, 2006), leaving Ci transport largely a mystery.…”

The Chlamydomonas reinhardtii Nar1 Gene Encodes a Chloroplast Membrane Protein Involved in Nitrite Transport

“…Alternatively, other anion transporters could also transport nitrite. Recently, a transporter encoded by a plastidic gene has been shown to transport bicarbonate in Chlamydomonas (Rolland et al, 1997), and formate, bicarbonate, and nitrite are chemically similar molecules.…”

The Plastid Genome-Encoded Ycf4 Protein Functions as a Nonessential Assembly Factor for Photosystem I in Higher Plants

“…The ycf4 gene is part of a gene cluster in the large single-copy region of the tobacco plastid genome, which comprises the psaI gene (encoding a small nonessential subunit of PSI; Schöttler et al, 2011) upstream of ycf4 and the genes ycf10 (encoding a nonessential membrane protein possibly involved in inorganic carbon uptake into the chloroplast; Rolland et al, 1997) and petA (encoding the cytochrome f subunit of the cytochrome b 6 f complex [Cyt bf]) downstream of ycf4 (Fig. 1A).…”

“…1A), petA mRNA accumulation was analyzed. petA was chosen because, unlike psaI and ycf10 (whose knockout does not result in a mutant phenotype; Rolland et al, 1997;Schöttler et al, 2011; S. Ruf, K. Krech, D. Bednarczyk, M.A. Schöttler, and R. Bock, unpublished data), it encodes an essential protein for photosynthesis.…”