Genetic structure and regulation of isoprene synthase in Poplar (Populus spp.)

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 synthase 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 developmentally 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

A unified mechanism of action for volatile isoprenoids in plant abiotic stress

The sessile nature of plants has resulted in the evolution of an extraordinarily diverse suite of protective mechanisms against biotic and abiotic stresses. Though volatile isoprenoids are known to be involved in many types of biotic interactions, they also play important but relatively unappreciated roles in abiotic stress responses. We review those roles, discuss the proposed mechanistic explanations and examine the evolutionary significance of volatile isoprenoid emission. We note that abiotic stress responses generically involve production of reactive oxygen species in plant cells, and volatile isoprenoids mitigate the effects of oxidative stress by mediating the oxidative status of the plant. On the basis of these observations, we propose a 'single biochemical mechanism for multiple physiological stressors' model, whereby the protective effect against abiotic stress is exerted through direct or indirect improvement in resistance to damage by reactive oxygen species