BackgroundAs key regulators of gene expression in eukaryotes, small RNAs have been characterized in many seed plants, and pathways for their biogenesis, degradation, and action have been defined in model angiosperms. However, both small RNAs themselves and small RNA pathways are not well characterized in other land plants such as lycophytes and ferns, preventing a comprehensive evolutionary perspective on small RNAs in land plants.ResultsUsing 25 representatives from major lineages of lycophytes and ferns, most of which lack sequenced genomes, we characterized small RNAs and small RNA pathways in these plants. We identified homologs of DICER-LIKE (DCL), ARGONAUTE (AGO), and other genes involved in small RNA pathways, predicted over 2600 conserved microRNA (miRNA) candidates, and performed phylogenetic analyses on small RNA pathways as well as miRNAs. Pathways underlying miRNA biogenesis, degradation, and activity were established in the common ancestor of land plants, but the 24-nucleotide siRNA pathway that guides DNA methylation is incomplete in sister species of seed plants, especially lycophytes. We show that the functional diversification of key gene families such as DCL and AGO as observed in angiosperms occurred early in land plants followed by parallel expansion of the AGO family in ferns and angiosperms. We uncovered a conserved AGO subfamily absent in angiosperms.ConclusionsOur phylogenetic analyses of miRNAs in bryophytes, lycophytes, ferns, and angiosperms refine the time-of-origin for conserved miRNA families as well as small RNA machinery in land plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-017-1291-2) contains supplementary material, which is available to authorized users.

This study demonstrates that DNA barcoding (i.e. reference databasing, tissue-direct PCR and molecular analysis), especially the trnL-F region, is an efficient tool to identify field gametophytes, and has considerable potential in exploring the ecology of fern gametophytes.

A low-cost and efficient photocatalytic reactor for environmental treatment and green technology was presented. ZnO nanorods firmly growing on polycarbonate optical disk substrate are generally perpendicular to the substrate as the immobilized photocatalyst of the spinning disk reactor. The photocatalytic efficiency and durability of the ZnO nanorods are effectively demonstrated.

A vittarioid fern (Pteridaceae) distributed in Eastern Asia is described here as a new species, Haplopteris heterophylla, which has long been included in H. hainanensis. A description, illustration, distribution, ecology, and a key to congeneric relatives of the new species are provided. Obovoid-shaped paraphyses and frond dimorphism are the diagnostic characteristics of H. heterophylla. In a trnL-F + matK + ndhF phylogeny of 14 Asian Haplopteris species, including H. hainanensis, both morphological obser\'ations and the cpDNA phylogeny support the systematic uniqueness of H. heterophylla.

is described and illustrated based on the results of detailed morphological comparison and molecular phylogenetic analysis. Morphologically, Haplopteris mindanaoensis is characterised by having obovoid (rather than funnel-shaped) soral paraphyses and deep soral grooves with asymmetrical flaps. Analysis of a combined four gene (chlL, matK, ndhF, and trnL-F) plastid data set shows that: (1) the two included samples of Haplopteris mindanaoensis have the same distinct haplotype; (2) Haplopteris mindanaoensis diverges early within the clade where most species with marginal soral grooves are placed; and (3) Haplopteris heterophylla C.W.Chen, Y.H.Chang & Yea C.Liu, the only other Haplopteris C.Presl species known to have obovoid paraphyses, is not closely related to H. mindanaoensis. The status of Haplopteris amboinensis (Fée) X.C.Zhang in China and Indochina is also clarified and a new combination, H. ensata (Christ) C.W.Chen & S.Linds. is made.