Synthesis of Rubisco gene products is upregulated by increasing the copy number of rbcL gene in Chlamydomonas chloroplast genome, without increased accumulation of the two Rubisco subunits

Abstract

In an attempt to increase the amount of Rubisco in a green alga, the Chlamydomonas reinhardtii rbcL gene connected to the aadA cassette was integrated into chloroplast inverted repeats in this organism to generate a transformant with three copies of rbcL (3L). Synthesis and accumulation of the rbcL transcript in 3L were 2.3 and 1.4 times those of the control, respectively. Although synthesis of the large subunit (LSU) in 3L was 2.6 times that in the control, accumulation of the LSU was only 1.1 times that in the control. Synthesis of rbcS transcript and the small subunit (SSU) in 3L was also upregulated to 1.7 and 1.3 times those in the control, respectively, while their accumulation was unaffected. These results suggest that an increase in rbcL gene number upregulates transcription of rbcL from chloroplast genomes and that of rbcS from a nuclear genome, but does not affect the accumulation of LSU and SSU.