Genetic structure and regulation of isoprene synthase in Poplar (Populus spp.) Claudia E. Vickers • Malcolm Possell • C. Nicholas Hewitt • Philip M. Mullineaux Received: 14 March 2010 / Accepted: 26 April 2010 / Published online: 14 May 2010 Ó Springer Science+Business Media B.V. 2010 Abstract Isoprene is a volatile 5-carbon hydrocarbon derived from the chloroplastic methylerythritol 2-C-methyl- D-erythritol 4-phosphate isoprenoid pathway. In plants, isoprene emission is controlled by the enzyme isoprene synthase; however, there is still relatively little known about the genetics and regulation of this enzyme. Isoprene syn- thase gene structure was analysed in three poplar species. It was found that genes encoding stromal isoprene synthase exist as a small gene family, the members of which encode virtually identical proteins and are differentially regulated. Accumulation of isoprene synthase protein is developmen- tally regulated, but does not differ between sun and shade leaves and does not increase when heat stress is applied. Our data suggest that, in mature leaves, isoprene emission rates are primarily determined by substrate (dimethylallyl diphosphate, DMADP) availability. In immature leaves, where isoprene synthase levels are variable, emission levels are also influenced by the amount of isoprene synthase protein. No thylakoid isoforms could be identified in Populus alba or in Salix babylonica. Together, these data show that control of isoprene emission at the genetic level is far more complicated than previously assumed. Keywords Isoprene Á Poplar Á Isoprene synthase Á Developmental regulation Á Isoprenoid pathway Introduction Isoprene (2-methyl-1,3-butadiene, C 5 H 8 ) is a volatile hydrocarbon emitted by animals, bacteria and many C 3 plant species (Sharkey 1996). Global emissions from plant sour- ces are massive: 500–750 Tg isoprene (440–660 Tg carbon) per year, which is roughly equivalent to global methane emissions and comprises approximately one-third of total global non-methane volatile organic carbon emissions (Guenther et al. 1995, 2006; Wang and Shallcross 2000). Although it is not in itself a greenhouse gas, isoprene is highly reactive and has a major impact on atmospheric chemistry (Shallcross and Monks 2000). Isoprene affects the oxidative capacity of the troposphere (Pierce et al. 1998; Poisson et al. 2000; Shallcross and Monks 2000; Thompson 1992); this may impact on the residence time of methane (Shallcross and Monks 2000). Isoprene also contributes to local pollution by reacting with other gas species to form secondary organic aerosol particles, ozone and carbon monoxide (Chameides et al. 1998; Claeys et al. 2004; Gra- nier et al. 2000; Pierce et al. 1998; Trainer et al. 1987). Isoprene therefore plays multiple important roles in the Earth system (Laothawornkitkul et al. 2009). Isoprene is expensive for plants to produce in terms of carbon and energy (Sharkey and Yeh 2001), and can rep- resent a loss of a significant proportion of recently-fixed carbon, particularly under stress conditions (Harley et al. 1996; Loreto and Delfine 2000; Sharkey and Loreto 1993). Electronic supplementary material The online version of this article (doi:10.1007/s11103-010-9642-3) contains supplementary material, which is available to authorized users. C. E. Vickers Á P. M. Mullineaux Department of Biological Sciences, Essex University, Colchester C04 3SQ, UK M. Possell Á C. Nicholas Hewitt Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK C. E. Vickers (&) Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, 4072 St Lucia, QLD, Australia e-mail: c.vickers@uq.edu.au 123 Plant Mol Biol (2010) 73:547–558 DOI 10.1007/s11103-010-9642-3