PARENT SESSION

Symposium S3C C3 and Rubisco
Tuesday August 31st, 2004 10:20 AM-12:20 PM Room 510A
Chair: Michael Salvucci
Co-Chair: Akiho Yokota

Transplanting sunflower rubisco subunits into tobacco chloroplasts – strategies and consequences. Robert Sharwood^*,1, Spencer Whitney¹, John Andrews¹, ¹ Molecular Plant Physiology, Research School of Biological Sciences, Canberra, ACT, Australia

ABSTRACT- In higher plants, Rubisco's eight identical large subunits are encoded by the rbcL gene on the plastome, while the eight small subunits are encoded by a nuclear RbcS multigene family. Maximal function requires perfect complementarity between the large and small subunits; interspecific subunit hybrids are invariably impaired catalytically. Thus, when the tobacco rbcL gene was replaced with the sunflower counterpart by plastid transformation, the resulting hybrid Rubisco with sunflower large subunits and tobacco small subunits had a decreased catalytic rate and impaired substrate affinity and was unable to support the growth of the plant in normal air [Kanevski et al., Plant Physiology (1999) 119: 133-141]. However, we have found that atmospheric CO₂ supplementation does allow this hybrid Rubisco to support photoautotrophic growth. We will present a physiological and biochemical characterisation of photosynthesis and growth by these plants that allows assessment of the catalytic performance of this hybrid Rubisco in vivo. Two strategies for providing the transplanted sunflower large subunits in tobacco with their cognate small subunits will be described. These entail transformation of sunflower RbcS into either nucleus or plastid genomes of transformants with sunflower rbcL gene in the plastome.

KEY WORDS: photosynthesis, CO₂-fixation, rubisco, plastid transformation