School of Natural Resources and the Environment and Laboratory for Tree Ring Research, University of Arizona, Tucson, AZ 85721, USA.
Plant Cell Environ. 2013 Mar;36(3):503-16. doi: 10.1111/pce.12015. Epub 2012 Oct 19.
Isoprene (2-methyl-1,3-butadiene) is emitted from many plants and it appears to have an adaptive role in protecting leaves from abiotic stress. However, only some species emit isoprene. Isoprene emission has appeared and been lost many times independently during the evolution of plants. As an example, our phylogenetic analysis shows that isoprene emission is likely ancestral within the family Fabaceae (= Leguminosae), but that it has been lost at least 16 times and secondarily gained at least 10 times through independent evolutionary events. Within the division Pteridophyta (ferns), we conservatively estimate that isoprene emissions have been gained five times and lost two times through independent evolutionary events. Within the genus Quercus (oaks), isoprene emissions have been lost from one clade, but replaced by a novel type of light-dependent monoterpene emissions that uses the same metabolic pathways and substrates as isoprene emissions. This novel type of monoterpene emissions has appeared at least twice independently within Quercus, and has been lost from 9% of the individuals within a single population of Quercus suber. Gain and loss of gene function for isoprene synthase is possible through relatively few mutations. Thus, this trait appears frequently in lineages; but, once it appears, the time available for evolutionary radiation into environments that select for the trait is short relative to the time required for mutations capable of producing a non-functional isoprene synthase gene. The high frequency of gains and losses of the trait and its heterogeneous taxonomic distribution in plants may be explained by the relatively few mutations necessary to produce or lose the isoprene synthase gene combined with the assumption that isoprene emission is advantageous in a narrow range of environments and phenotypes.
异戊二烯（2-甲基-1,3-丁二烯）由许多植物排放，它似乎在保护叶片免受非生物胁迫方面具有适应性作用。然而，只有一些物种会排放异戊二烯。异戊二烯的排放在植物的进化过程中已经独立出现和消失了很多次。例如，我们的系统发育分析表明，异戊二烯的排放在豆科（=豆科）中可能是祖先的，但它已经至少丢失了 16 次，并通过独立的进化事件再次获得了至少 10 次。在蕨类植物（蕨类植物）中，我们保守地估计，异戊二烯的排放已经通过独立的进化事件获得了 5 次，失去了 2 次。在栎属（栎属）中，异戊二烯的排放已经从一个分支中丢失，但被一种新型的光依赖性单萜类化合物的排放所取代，这种新型的单萜类化合物的排放使用与异戊二烯的排放相同的代谢途径和底物。这种新型的单萜类化合物的排放已经在栎属中至少独立出现了两次，并且已经从栎属的一个单一种群的 9%个体中丢失。异戊二烯合酶的基因功能的获得和丧失是可能的，通过相对较少的突变。因此，这种特征在谱系中经常出现；但是，一旦出现，用于进化辐射到选择该特征的环境中的时间相对于能够产生无功能的异戊二烯合酶基因的突变所需的时间是短暂的。该特征的频繁获得和丧失及其在植物中的异质分类分布可能是由产生或丧失异戊二烯合酶基因所需的相对较少的突变与假设异戊二烯的排放在狭窄的环境和表型范围内有利相结合所解释的。
