First report on the mitogenome of the aquatic plant Myriophyllum ussuriense in Haloragaceae and its implications for aquatic adaptation

Abstract

Myriophyllum, a representative submerged genus within the family Haloragaceae, serves as a key material for investigating terrestrial-to-aquatic evolutionary transitions. Despite its ecological significance, studies on the mitogenome of this genus remain limited. In this study, we utilized HiFi sequencing data of M. ussuriense to assemble into circular mitogenome and plastome, measuring 765,982 bp and 158,484 bp, respectively. A total of 234 SSRs and 367 long dispersed repeats were identified, which likely contributed to the mitogenome expansion relative to other Saxifragales species. Furthermore, 23 mitochondrial-to-plastid transfer sequences (MTPTs) were detected, potentially driven by the abundance of long dispersed repeats. Compared to terrestrial plants within Saxifragales, the M. ussuriense mitogenome displayed a significantly reduced number of RNA editing sites (215), possibly reflecting the stability of aquatic environments. However, three nad genes (nad1, nad4, and nad7) exhibited an increased number of RNA editing sites, likely supporting adaptation to hypoxic conditions. In addition, most mitochondrial protein-coding genes (PCGs) were subject to purifying selection, although positive selection signals were detected in ccmB and atp4, suggesting their involvement in aquatic adaptation. In conclusion, our findings will offer new insights into the mitogenomic characteristics and aquatic adaptation of Myriophyllum, providing a valuable foundation for further evolutionary and ecological studies.