Identification of physiological functions of isoprene emission

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Trees like poplar synthesize and emit high amounts of the volatile carbohydrate isoprene, whereas herbs are low isoprene emitters. One function of isoprene biosynthesis in plants is to increase the temperature tolerance of leaves during periodes of high temperature. As poplar hybrids are important plants in forestry, as the isoprene synthase gene is available from poplar and as these trees are transformable, it is aimed to prove the role of the isoprene formation as a trait to overcome heat stress conditions and to deliver poplar strains with an increased thermotolerance. Initially, transgenic poplar lines will be produced and selected that over-express genes of the isoprene biosynthesis by introducing alternatively (i) an initial gene of the isoprene biosynthesis or (ii) the isoprene synthase recently isolated from P. alba x tremula cloned behind the 35S CaMV promotor and/or leaf tissue nuclear coded photosynthesis specific promotors. The expression in the leaves will be controlled on mRNA level, on protein level and by measuring the isoprene emission. The stability of the phenotype will be studied. To obtain negative control plants it is aimed to suppress isoprene emission by the RNAi technique. Isoprene formation and the thermotolerance of these transgenic plants will be studied under controlled light, temperature and humidity conditions in comparison to the wildtype. Finally strains will be selected that are better adopted to heat periods expected to occur more frequently in the near future due to global warming.