Comparative analysis of plastome structure in Sphagnum species from China

Sphagnum L. (peat mosses) comprises approximately 291 recognized species distributed worldwide except Antarctica. Plastomes are useful for investigating structure evolution and phylogeny due to their conserved structure. However, Sphagnum species endemic to China have been underrepresented in plastome-based studies, hindering a comprehensive understanding of their evolutionary history.

Analysis of 13 plastomes of eight Sphagnum species from China, revealed both inter-and intraspecific variations. Plastome sizes ranged from 138,958 bp (S. acutifolioides) to 141,257 bp (S. ovatum), with conserved gene content (86 CDSs, 37 tRNAs, 8 rRNAs). All plastomes exhibited a typical quadripartite structure: LSC (96,896-99,205 bp), SSC (21,187-21,381 bp), and IRs (10,298-10,391 bp). The IR boundaries and adjacent genes were consistent, except in S. squarrosum, where chIL entered IRb and ndhF entered IRa. Premature termination of the petN gene was detected in all species except S. medium and S. palustre (population: GZ and HB). Codons with RSCU > 1.00 favored A/U at the third position, with UUA (Leucine) and GCU (Alanine) being most common. SSRs dominated by mono- and di-repeats, with tri-repeats were highly conserved. Phylogenetic analysis supported the placement of S. ovatum, S. subsecundum, and S. acutifolioides in subgenus Subsecunda; S. medium and S. palustre in subgenus Sphagnum; and S. warnstorfii, S. fuscum, and S. squarrosum in subgenus Acutifolia.

Despite overall structural conservation, expanded sampling revealed both inter- and intraspecific plastome variation in Sphagnum, underscoring the utility of plastomes for phylogenetic inference and assessing genetic diversity. These findings enhance our understanding of Chinese Sphagnum species and their evolutionary relationships.