Thalictrum

Abstract: The chloroplast genes atpB and rbcL and nuclear ribosomal 18S DNA were sequenced for 23 genera of the Ranunculaceae and two outgroup taxa (Hydrastis and Glaucidium). The three sequence data sets were combined and the resulting preliminary phylogenetic tree used to assess relationships within the Ranunculaceae. The phylogeny strongly supports the monophyly of the family, with 26 substitutions, a bootstrap value of 98% and a decay index of > 7. Within the family, the T-type chromosome group is basal and paraphyletic with respect to the larger R-type chromosome group. Within the T-type chromosome group, Coptis and Xanthorhiza from a monophyletic group and are basal to all other Ranunculaceae. Other alliances previously proposed by taxonomists are confirmed: Anemonella/Thalictrum/ lsopyrum/Aquilegia/Semiaquilegia; Anemone/Clematis, Trautvetteria/ Myosurus/Ranunculus; Aconitum/Delphinium; and Anemonopsis/Cimicifugal/Actaea. Other groupings that could not have been predicted on the basis of traditional data include a clade consisting of Adonis and Trollius and the inclusion of Eranthis in a clade with Anemonopsis, Cimicifuga, and Actaea. Nigella is weakly allied with a clade consisting of Aconitum and Delphinium. The molecular sequence data are largely congruent with results based on cytology, phytochemistry, and micromorphology. Flower and fruit characters are homoplastic in relation to the cladogram based on sequence data. The pattern of relationships based on sequence data supports the view that staminodia/petals and achenes have evolved independently several times within the Ranunculaceae.

Abstract: Plastids originated from cyanobacteria and the majority of the ancestral genes were lost or functionally transferred to the nucleus after endosymbiosis. Comparative genomic investigations have shown that gene transfer from plastids to the nucleus is an ongoing evolutionary process but molecular evidence for recent functional gene transfers among seed plants have only been documented for the four genes accD, infA, rpl22, and rpl32. The complete plastid genome of Thalictrum coreanum, the first from the subfamily Thalictroideae (Ranunculaceae), was sequenced and revealed the losses of two genes, infA and rpl32. The functional transfer of these two genes to the nucleus in Thalictrum was verified by examination of nuclear transcriptomes. A survey of the phylogenetic distribution of the rpl32 loss was performed using 17 species of Thalictrum and representatives of related genera in the subfamily Thalictroideae. The plastid-encoded rpl32 gene is likely nonfunctional in members of the subfamily Thalictroideae (Aquilegia, Enemion, Isopyrum, Leptopyrum, Paraquilegia, and Semiaquilegia) including 17 Thalictrum species due to the presence of indels that disrupt the reading frame. A nuclear-encoded rpl32 with high sequence identity was identified in both Thalictrum and Aquilegia. The phylogenetic distribution of this gene loss/transfer and the high level of sequence similarity in transit peptides suggest a single transfer of the plastid-encoded rpl32 to the nucleus in the ancestor of the subfamily Thalictroideae approximately 20–32 Mya. The genome sequence of Thalictrum coreanum provides valuable information for improving the understanding of the evolution of plastid genomes within Ranunculaceae and across angiosperms. Thalictrum is unusual among the three sequenced Ranunculaceae plastid genomes in the loss of two genes infA and rpl32, which have been functionally transferred to the nucleus. In the case of rpl32 this represents the third documented independent transfer from the plastid to the nucleus with the other two transfers occurring in the unrelated angiosperm families Rhizophoraceae and Salicaceae. Furthermore, the transfer of rpl32 provides additional molecular evidence for the monophyly of the subfamily Thalictroideae.

Abstract: Perennial woodland herbs in the genus Thalictrum exhibit high diversity of floral morphology, including four breeding and two pollination systems. Their phylogenetic position, in the early-diverging eudicots, makes them especially suitable for exploring the evolution of floral traits and the fate of gene paralogs that may have shaped the radiation of the eudicots. A current limitation in evolution of plant development studies is the lack of genetic tools for conducting functional assays in key taxa spanning the angiosperm phylogeny. We first show that virus-induced gene silencing (VIGS) of a PHYTOENE DESATURASE ortholog (TdPDS) can be achieved in Thalictrum dioicum with an efficiency of 42% and a survival rate of 97%, using tobacco rattle virus (TRV) vectors. The photobleached leaf phenotype of silenced plants significantly correlates with the down-regulation of endogenous TdPDS (P<0.05), as compared to controls. Floral silencing of PDS was achieved in the faster flowering spring ephemeral T. thalictroides. In its close relative, T. clavatum, silencing of the floral MADS box gene AGAMOUS (AG) resulted in strong homeotic conversions of floral organs. In conclusion, we set forth our optimized protocol for VIGS by vacuum-infiltration of Thalictrum seedlings or dormant tubers as a reference for the research community. The three species reported here span the range of floral morphologies and pollination syndromes present in Thalictrum. The evidence presented on floral silencing of orthologs of the marker gene PDS and the floral homeotic gene AG will enable a comparative approach to the study of the evolution of flower development in this group.

Abstract: Thalictrum nanhuaense (Ranunculaceae), a new species from Nanhua in central Yunnan, China, is here illustrated and described. The new species is similar to T. fargesii in habit and having larger sepals up to 4 mm long and persistent at anthesis and straight styles, but differs by its succulent and tuberose (vs. fibrous and slender) roots, filiform (vs. clavate) filaments, point-like (vs. oblong and narrowly winged) stigmas, and subulate-terete (vs. lunate-fusiform) achenes.