Transgenic overexpression of Leucaena β-carbonic anhydrases in tobacco does not affect carbon assimilation and overall biomass

Abstract

The role of β-carbonic anhydrases (CAs) in C₃ plant carbon assimilation is not clear. In this study, the primary role of C₃ plant β-CAs in carbon assimilation was investigated for which, a chloroplastic β-CA gene (cacp) and a cytoplasmic β-CA gene (cacyt) from a C₃ tree-legume of tropics, Leucaena leucocephala (leucaena) were overexpressed in Nicotiana tabacum (tobacco). The cacp and cacyt β-CA isoforms from leucaena were overexpressed separately and also together in tobacco resulting in three types of transgenic tobacco plants (i) expressing cacp only (ii) expressing cacyt only and (iii) co-expressing both cacp and cacyt. These transgenic plants exhibited significantly higher activity of β-CAs as compared with wild-type plants. The percent increase in the CA activity of transgenic plants expressing leucaena cacyt or cacp was found to be ∼51 and ∼55%, respectively. The transgenic tobacco expressing both the leucaena β-CA isoforms exhibited ∼63% increase in CA activity as compared with the wild-type. However, despite notable increase in the CA activity of transgenic tobacco plants, no difference was observed in their phenotype, chlorophyll content and the overall dry weight compared with that of wild-type suggesting that C₃ β-CAs are not involved in active accumulation of inorganic carbon.

Keywords::

• carbonic anhydrase
• leucaena
• tobacco
• photosynthesis

Additional information

Funding

This research is supported by the National Science Foundation Award No. CBET 08-27057 and by HATCH [grant number HAW00551-H].