Journal of Experimental Botany, Vol. 54, No. 381, pp. 223-237,
January 2, 2003
© 2003 Oxford University Press
Expression of a cyanobacterial sucrose-phosphate synthase from Synechocystis sp. PCC 6803 in transgenic plants
Received 1 July 2002; Accepted 27 August 2002
CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia
1 Present address: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, D-14476 Golm, Germany.
2 To whom correspondence should be addressed. Fax: +61 2 6246 5000. E-mail: robert.furbank{at}csiro.au
Sucrose-phosphate synthase (SPS) from the cyanobacterium Synechocystis sp. PCC 6803 lacks all of the Ser residues known to be involved in the regulation of higher plant SPS by protein phosphorylation. The Synechocystis SPS is also not allosterically regulated by glucose 6-phosphate or orthophosphate. To investigate the effects of expressing a potentially unregulated SPS in plants, the Synechocystis sps gene was introduced into tobacco, rice and tomato under the control of constitutive promoters. The Synechocystis SPS protein was expressed at a high level in the plants, which should have been sufficient to increase overall SPS activity 2–8-fold in the leaves. However, SPS activities and carbon partitioning in leaves from transgenic and wild-type plants were not significantly different. The maximal light-saturated rates of photosynthesis in leaves from tomato plants expressing the Synechocystis SPS were the same as those from wild-type plants. Tomato plants expressing the maize SPS showed 2–3-fold increases in SPS activity, increased partitioning of photoassimilate to sucrose and up to 58% higher maximal rates of photosynthesis. To investigate the apparent inactivity of the Synechocystis SPS the enzyme was purified from transgenic tobacco and rice plants. Surprisingly, the purified enzyme was found to have full catalytic activity. It is proposed that some other protein in plant cells binds to the Synechocystis SPS resulting in inhibition of the enzyme.
Key words: Carbon partitioning, Lycopersicon esculentum Mill., Oryza sativa L., Nicotiana tabacum L., photosynthesis, rice, sucrose-phosphate synthase, Synechocystis sp. PCC 6803, tobacco, tomato.
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