Comparative plastid genomics of mycoheterotrophic and autotrophic plants

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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.