Variation of plastomes and their potential role in adaptive evolution of Poales
Peng-Fei Ma, Hong Wu, and De-Zhu Li

The monocot order Poales includes 16 families and more than 23,000 species, accounting for about 7% of the angiosperm and 33% of the monocot diversity, with significant value in ecology and economy. In our previous study, we reconstructed a robust phylogeny of Poales based mainly on plastomes. Substantial phylogenetic conflicts were also revealed within the plastid genomes of the order. Here, we investigated the variation patterns of its plastomes by analyses of 93 plastomes from 16 families and 5 clades of Poales. The plastomic variation of Poales was diverse, including genome size, gene content, GC content, inverted repeat (IR) type and IR shift. For example, the Poales possessed the largest plastome of monocots, having a size of 225,293 bp and about twice of the smallest one (126,519 bp) in the same order. We also found an unexpected variety of IR types, especially the three IR copies in two sampled species, which, to the best of our knowledge, is the first such report in angiosperms. The repetitive sequences in plastomes of Poales were closely related their inversions and rearrangements. We also found the loss of ndh genes and variation of GC content may be an adaptation to swampy or wetland habitats. And four plastid genes were identified as positively selected, which may be related to the diverse habitats and the C3-C4 photosynthetic transition in Poales. Our findings provide new insights into the plastomic evolution of Poales, as well as for the angiosperms as a whole.

свернуть