The complete plastome of the Antarctic moss Andreaea regularis (Andreaeaceae) and its comparative analyses within...

Andreaeopsida represents a distinct group of nonperistomate mosses, characterized by its phylogenetic position as a sister to peristomate species. However, plastome data for this lineage remains scarce, limiting our understanding of its genomic features and the evolution of plastome within Bryophyta. To bridge this gap, we sequenced the plastome of Andreaea regularis, a prominent species within the Andreaeopsida, found in Antarctica. This study aims to characterize the plastome of A. regularis and compare its features across nonperistomate and peristomate moss lineages, focusing on phylogenetic placement, plastome characteristics variations, and potential selection pressures.

The assembled plastome of A. regularis spans 135,217 bp with 30.3% GC content and 122 annotated genes. Phylogenetic analysis confirms the position of A. regularis among the nonperistomate mosses, forming a sister group to the peristomate lineage. Comparative analysis reveals a reduction pattern in plastome size, GC content, and protein-coding gene (PCG) content along the evolutionary trajectory from nonperistomate mosses to peristomate mosses, with A. regularis exhibiting intermediate characteristics. This pattern is mirrored by structural variation in the large single-copy (LSC) region, where A. regularis retains more PCGs and exhibits lower deletion rates than peristomate species but shows signs of genome contraction relative to nonperistomate mosses. Correlation analysis further indicates that total plastome size and GC content are most strongly associated with LSC length (r = 0.994) and GC content (r = 0.999), respectively, suggesting that LSC variation is closely linked to plastome structural differences among mosses. Purifying selection is prevalent across genic regions in mosses, while codon usage patterns remain minimally affected by mutational pressure. The genes rpoC2 and ndhF exhibit dynamic evolution, marked by elevated nonsynonymous substitution rates, high nucleotide diversity, and numerous diagnostic sites. Additionally, positively selected residues in these genes, alongside those in rbcL, indicate potential evolutionary pressures in A. regularis.

Altogether, this study establishes a critical genomic reference for Andreaeopsida, advances our understanding of nonperistomate-peristomate plastome evolution, and highlights the intricate nucleotide variation underlying plastome diversity and evolutionary differentiation in mosses.