Increased Rubisco Content in Transgenic Rice Transformed with the ‘Sense’ rbcS Gene

Abstract

Rice (Oryza sativa L.) plants with substantially increased Rubisco content were obtained by Agrobacteriummediated transformation with the rice rbcS sense gene under the control of the rice rbcS promoter. The primary transformants were screened for the ratio of Rubisco to leaf-N content, and the transformants with 4120% wild-type levels of Rubisco were selected. In the progeny of the selected lines of the transformants, the mRNA levels of one member of the rbcS gene family were increased from 3.9-to 6.2-fold, whereas those of other members of the rbcS gene family were unchanged. The total levels of rbcS mRNA were increased from 2.1-to 2.8-fold. The levels of rbcL mRNA were increased from 1.2-to 1.9-fold. Rubisco protein content was significantly increased by 30% on a leaf area basis. The ratio of Rubisco-N to leaf-N was also increased by 10-20%, irrespective of N treatment. The specific activity of Rubisco per unit of enzyme protein was not different. However, light-saturated photosynthesis was not enhanced even when the rate was measured at low [CO 2 ] where Rubisco becomes limiting for photosynthesis. Some lines showed lower photosynthesis at high [CO 2 ] (460 Pa). We conclude that introduction of additional sense rbcS leads to overexpression of rbcS and that this overexpression slightly up-regulates the gene expression of rbcL at the transcript level and enhances the amount of Rubisco holoenzyme. However, overproduction of Rubisco protein does not improve photosynthesis.

【Short Report】Effects of Nitrogen on the Expression of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Small Subunit Multigene Family Members in Rice (Oryza sativa L.)

“…OsRBCS1 transcripts were not detectable (data not shown). This result was consistent with that of Suzuki et al (2007). The levels of OsRBCS2, OsRBCS3, OsRBCS4 and OsRBCS5 mRNAs increased in response to NH 4 NO 3 supply (Fig.1).…”

“…These results indicate that the expression of the rbcS multigene family members is differently regulated by N in rice. Suzuki et al (2007) reported that OsRBCS1 was only slightly expressed, and the expression of OsRBCS2, OsRBCS3, OsRBCS4 and OsRBCS5 was enhanced to the same relative degree with increasing N supply. In addition, the amino acid sequences except the transit peptide, deduced from rice four rbcS genes except for OsRBCS1, are 100% identical.…”

“…In addition, the amino acid sequences except the transit peptide, deduced from rice four rbcS genes except for OsRBCS1, are 100% identical. Suzuki et al (2007) hypothesized that adaptation of Rubisco to changes in N availability does not occur through the specific expression of five members of the rice rbcS multigene family. However, according to the data presented in Fig.…”

“…Rubisco is composed of eight small subunits (rbcS) encoded by a nuclear multigene family and eight large subunits encoded by a single gene in the multicopy chloroplast genome. In rice, Oryza sativa, the rbcS multigene family consists of 5 members designated as OsRBCS1, 2, 3, 4 and 5 (AK059909, AK121444, AK068555, AK070257 and AK099574, respectively; Suzuki et al, 2007). OsRBCS1 mRNA levels in leaf blades were very limited 【Short Report】 (Suzuki et al, 2009).…”

“…OsRBCS1 mRNA levels in leaf blades were very limited 【Short Report】 (Suzuki et al, 2009). The expression of OsRBCS2, 3, 4 and 5 genes was enhanced similarly with increasing nitrogen supply (Suzuki et al, 2007). However, no sequence identity was found in the promoter regions of the rbcS multigene family members, and very limited data is available on the expression of the rbcS multigene family members in response to N supply and N signals that regulate the gene expression.…”