Comparative plastid genomics of mycoheterotrophic and autotrophic plants

质体（在绿色组织中称为叶绿体）是植物用来将阳光转化为能量（以糖的形式）的细胞器。许多寄生植物，比如菟丝子，会从邻近的植物那里偷取糖分和其他营养物质，因此它们往往已经退化，或者在它们特殊的质体基因组中失去了任何光合作用基因。真菌异养植物，如印度管，更进一步，在一个由真菌组成的地下网络上“欺骗”，真菌与绿色植物生活在互利的伙伴关系中（真菌支持植物从土壤中吸收营养，植物提供富含能量的化合物作为回报）。真菌异养植物不是相互依存的伙伴，而是从参与这个地下网络的真菌中窃取糖和其他营养物质。因此，异养真菌植物，如寄生植物，预计会在其质体基因组中显示出光合作用基因的退化（“要么使用它，要么失去它”）。降解的程度应取决于真菌异养植物对偷窃养分的依赖程度。我们的研究将通过比较这些天然光合“突变体”的质体基因组与仍然进行光合作用的相关物种的质体基因组，来研究与这种不寻常的植物营养模式相关的质体基因组降解模式。通过展示非光合作用基因（也可能是一些具有次要功能的光合作用基因）在不同真菌异养植物群体中的保留模式，本研究将为质体的功能和进化提供新的见解。

Plastids (called chloroplasts in green tissue) are the cellular organelles that plants use to convert sunlight into energy, in the form of sugar. Many parasitic plants, such as dodder, steal sugar and other nutrients from neighbouring plants, and so they tend to have degraded or lost any photosynthesis genes in their specialized plastid genomes. The mycoheterotrophic plants, such as indian pipes, take this one step further and 'cheat' on an underground network that consists of fungi living in a mutually beneficial partnership with green plants (the fungi support nutrient uptake from the soil for the plants, and the plants provide energy-rich compounds to return the favour). Instead of being mutualistic partners, the mycoheterotrophic plants steal sugars and other nutrients from fungi involved in this underground web. Mycoheterotrophic plants, like parasitic plants, are therefore expected to show degradation in photosynthesis genes in their plastid genome ('use it or lose it'). The degree of degradation should depend on how much mycoheterotrophic plants rely on stolen nutrients. Our study will examine patterns of plastid genome degradation associated with this unusual mode of plant nutrition, by comparing the plastid genomes of these natural photosynthetic 'mutants' to related species that still photosynthesize. By demonstrating the patterns of retention of non-photosynthetic genes (and likely also of some photosynthetic genes with secondary functions) in different groups of mycoheterotrophic plants, this study will offer new insights into how plastids function and evolve.