Rapid radiations of both kiwifruit hybrid lineages and their parents shed light on a two-layer mode of species diversification.

Reticulate speciation caused by interspecific hybridization is now recognized as an important mechanism in the creation of biological diversity. However, depicting the patterns of phylogenetic networks for lineages that have undergone interspecific gene flow is challenging. Here we sequenced 25 taxa representing natural diversity in the genus Actinidia with an average mapping depth of 26× on the reference genome to reconstruct their reticulate history. We found evidence, including significant gene tree discordance, cytonuclear conflicts, and changes in genome-wide heterozygosity across taxa, collectively supporting extensive reticulation in the genus. Furthermore, at least two separate parental species pairs were involved in the repeated origin of the hybrid lineages, in some of which a further phase of syngameon was triggered. On the basis of the elucidated hybridization relationships, we obtained a highly resolved backbone phylogeny consisting of taxa exhibiting no evidence of hybrid origin. The backbone taxa have distinct demographic histories and are the product of recent rounds of rapid radiations via sorting of ancestral variation under variable climatic and ecological conditions. Our results suggest a mode for consecutive plant diversification through two layers of radiations, consisting of the rapid evolution of backbone lineages and the formation of hybrid swarms derived from these lineages.

Isolation and functional characterization of a R2R3-MYB regulator of the anthocyanin biosynthetic pathway from Epimedium sagittatum.

KEY MESSAGE: A R2R3-MYB transcription factor EsAN2 was isolated from Epimedium sagittatum and functionally characterized to regulate the anthocyanin biosynthetic pathway. Epimedium plants are used widely both as traditional Chinese medicinal herbs and ornamental perennials. Anthocyanins, acting as major contributors to plant color diversity, their biosynthesis are regulated by a series of transcription factors, including MYB, bHLH and WD40 protein. Previously, a MYB transcription factor involved in regulation of the anthocyanin pathway from Epimedium sagittatum, EsMYBA1 has been isolated, but was found to be expressed mostly in leaves. In this research, another MYB transcription factor, designated as EsAN2, was isolated from flowers by the screening of E. sagittatum EST database. Preferential expression of EsAN2 in flowers and flower buds was found. Ectopic expression of EsAN2 in tobacco significantly enhanced the anthocyanin biosynthesis and accumulation, both in leaves and flowers. Most structural genes of the anthocyanin biosynthetic pathway were strongly upregulated, as well as two bHLH regulators (NtAn1a and NtAn1b) in old leaves of tobacco overexpressing EsAN2, compared to the control plants. While only three structural genes, chalcone synthase (CHS), chalcone isomerase (CHI) and anthocyanidin synthase (ANS), were upregulated by EsAN2 ectopic expression in tobacco flowers. Yeast two-hybrid assay showed that EsAN2 was capable of interacting with four bHLH regulators of the anthocyanin biosynthetic pathway. These results suggest that EsAN2 is involved in regulation of the anthocyanin biosynthesis in Epimedium flowers. Identification and characterization of EsAN2 provide insight into the coloration of Epimedium flowers and a potential candidate gene for metabolic engineering of flavonoids in the future.

The Complete Chloroplast Genome Sequences of Five Epimedium Species: Lights into Phylogenetic and Taxonomic Analyses.

Epimedium L. is a phylogenetically and economically important genus in the family Berberidaceae. We here sequenced the complete chloroplast (cp) genomes of four Epimedium species using Illumina sequencing technology via a combination of de novo and reference-guided assembly, which was also the first comprehensive cp genome analysis on Epimedium combining the cp genome sequence of E. koreanum previously reported. The five Epimedium cp genomes exhibited typical quadripartite and circular structure that was rather conserved in genomic structure and the synteny of gene order. However, these cp genomes presented obvious variations at the boundaries of the four regions because of the expansion and contraction of the inverted repeat (IR) region and the single-copy (SC) boundary regions. The trnQ-UUG duplication occurred in the five Epimedium cp genomes, which was not found in the other basal eudicotyledons. The rapidly evolving cp genome regions were detected among the five cp genomes, as well as the difference of simple sequence repeats (SSR) and repeat sequence were identified. Phylogenetic relationships among the five Epimedium species based on their cp genomes showed accordance with the updated system of the genus on the whole, but reminded that the evolutionary relationships and the divisions of the genus need further investigation applying more evidences. The availability of these cp genomes provided valuable genetic information for accurately identifying species, taxonomy and phylogenetic resolution and evolution of Epimedium, and assist in exploration and utilization of Epimedium plants.