Identification of physiological functions of isoprene emission

像杨树这样的树木合成并释放出大量挥发性碳水化合物异戊二烯，而草本植物的异戊二烯排放量很低。异戊二烯生物合成在植物中的一个功能是在高温时期提高叶片的耐温性。由于杂交杨树是重要的林业植物，异戊二烯合成酶基因可从杨树中获得，而且这些树木是可转化的，因此旨在证明异戊二烯的形成是克服热胁迫条件的一种性状，并提供具有更高耐热性的杨树品系。首先，通过引入(i)异戊二烯生物合成的初始基因或（ii）最近从白杨中分离到的异戊二烯合成酶，在35S CaMV启动子和/或叶片组织核编码的光合作用特异性启动子后克隆，将产生并选择过表达异戊二烯生物合成基因的转基因杨树品系。其在叶片中的表达受mRNA水平、蛋白水平和异戊二烯释放量的控制。将对表型的稳定性进行研究。利用RNAi技术抑制异戊二烯的释放是获得阴性对照植物的目的。这些转基因植物的异戊二烯形成和耐热性将在受控光、温度和湿度条件下与野生型进行比较研究。最后，将选择更好地适应预计在不久的将来由于全球变暖而更频繁发生的热期的菌株。

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.