The most species-rich group of extant ferns (monilophytes), core leptosporangiates, have a distinct plastid genome (plastome) organization pattern from basal fern lineages. However, the details of genome structure transformation from ancestral ferns to core leptosporangiates remain unclear because of limited plastome data available.

To address this problem, Dr. GAO Lei and their colleagues, led by Prof. WANG Ting from Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden, recently determined the complete chloroplast genome sequences of Lygodiumjaponicum (Lygodiaceae), a member of schizaeoid ferns (Schizaeales), and Marsileacrenata (Marsileaceae), a representative of heterosporous ferns (Salviniales). The two species represent the sister and the basal lineages of core leptosporangiates, respectively, for which the plastome sequences were currently unavailable.

Comparative genomic analysis of all sequenced fern plastomes reveals that the gene order of L. japonicumplastome occupies an intermediate position between that of basal ferns and core leptosporangiates. The two exons of the fern ndhB gene have a unique pattern of intragenic copy number variances. Specifically,the substitution rate heterogeneity between the two exons is congruent with their copy number changes, confirming the constraint role that IRs may play on the substitution rate of chloroplast gene sequences.

The study entitled “Plastome sequences ofLygodium japonicumandMarsilea crenatareveal the genome organization transformation from basal ferns to core leptosporangiates” has been published in Genome Biology and Evolution.

This research was supported by National Natural Science Foundation of China, Knowledge Innovation Program of the Chinese Academy of Sciences, and the Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden, Chinese Academy of Sciences.

 ML tree of 18 taxa of 87 plastid genes (Image by Prof. WANG’s group)