Predicting Plastid Marker Variation: Can Complete Plastid Genomes from Closely Related Species Help?

Rapidly evolving non-coding plastid regions (NCPs) are currently widely used in evolutionary biology especially in plant systematic studies where NCPs have become one of the most commonly used tools in clarifying species relationships. Currently, the generally small amount of sequence variation provided by NCPs compared to nuclear regions makes plastid phylogeny reconstruction challenging at the species-level, especially so in species rich clades such as Solanum with c. 1,200 species. Previous studies have established that the set of most highly variable NCPs vary between major plant families, and here we explore whether this variation extends beyond family level to genera and major clades within genera. Using full plastome data, we identify the most highly variable plastid markers in the Potato clade of Solanum. We then compare sequence variation between the Potato and the closely related Morelloid clade. Results show that whilst a narrow set of NCPs show consistently high variation, levels of sequence variation in most NCPs differ greatly between the two closely related clades. The high variation detected between closely related groups implies that repeated screening studies will be needed for individual projects despite the potential availability of results from closely related taxa, and indicates a narrower applicability of family-specific screening studies than previously thought.