Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is a key enzyme in carbon fixation and has attracted significant interest as a potential target for the improvement of photosynthesis in crop plants. The enzyme consists of eight large (50 kDa) plastid-encoded subunits (L-subunit) and eight small (15 kDa) nuclear-encoded subunits (S-subunit) that assemble into an L₈S₈ functional enzyme in the plastid. Rubisco’s catalytic prowess in higher plants, albeit having its active site located within the L-subunit, requires the S-subunits for maximal activity. More recently, emphasis on the importance of the S-subunit on influencing Rubisco catalysis has been demonstrated by the over-expression of heterologous S-subunits in rice transgenics¹ .

So far, difficulties in modifying the S-subunits in plants have stemmed from the S-subunit being coded by a multi-gene family (RBCS). This has made the S-subunits virtually inaccessible for targeted mutagenesis, thus impeding studies on their structure and function.

We have generated a RNAi-RBCS tobacco line that completely prevents endogenous RBCS mRNA accumulation, therefore allowing studies on the influence of the S-subunit on Rubisco catalysis in higher plants. This transgenic line provides us with the capability to undertake structure-function analyses of recombinant L- and S-subunits using chloroplast transformation.

Presented will be data of bioengineered Rubisco comprising recombinant L- and S-subunits in the plastid. The work poses a proof-of-concept approach for examining the influence of both subunits on Rubisco catalysis. Such studies are hoped to identify structural solutions for improving Rubisco function in crop plants to help meet future global food demands.