The plastid genome of mycoheterotrophic monocot Petrosavia stellaris exhibits both gene losses and multiple rearrangements

Abstract

Plastid genomes of nonphotosynthetic plants represent a perfect model for studying evolution under relaxed selection pressure. However, the information on their sequences is still limited. We sequenced and assembled plastid genome of Petrosavia stellaris, a rare mycoheterotrophic monocot plant. After orchids, Petrosavia represents only the second family of nonphotosynthetic monocots to have its plastid genome examined. Several unusual features were found: retention of the ATP synthase genes and rbcL gene; extensive gene order rearrangement despite a relative lack of repeat sequences; an unusually short inverted repeat region that excludes most of the rDNA operon; and a lack of evidence for accelerated sequence evolution. Plastome of photosynthetic relative of P. stellaris, Japonolirion osense, has standard gene order and does not have the predisposition to inversions. Thus, the rearrangements in the P. stellaris plastome are the most likely associated with transition to heterotrophic way of life.

Keywords: Petrosaviales; gene loss; genome rearrangements; mycoheterotrophy; plastid genome.

Fig. 1.—

Circular map of the plastid genome of Petrosavia stellaris. Genes shown inside the circle are transcribed clockwise, those outside the circle are transcribed counterclockwise. Numbered curves outside of the map outline blocks colinear to non-rearranged plastid genomes.

Fig. 2.—

Phylogenetic tree inferred by RAxML using nucleotide sequences of 37 protein coding genes shared between 93 angiosperm plastid genomes. Branch length is proportional to number of nucleotide substitutions. Numbers above nodes indicate bootstrap values. Nodes with support less than 50% are collapsed.