DNA barcoding involves sequencing a standard region of DNA as a tool for species identification. However, there has been no agreement on which region(s) should be used for barcoding land plants. To provide a community recommendation on a standard plant barcode, we have compared the performance of 7 leading candidate plastid DNA regions (atpF-atpH spacer, matK gene, rbcL gene, rpoB gene, rpoC1 gene, psbK-psbI spacer, and trnH-psbA spacer). Based on assessments of recoverability, sequence quality, and levels of species discrimination, we recommend the 2-locus combination of rbcL؉matK as the plant barcode. This core 2-locus barcode will provide a universal framework for the routine use of DNA sequence data to identify specimens and contribute toward the discovery of overlooked species of land plants.matK ͉ rbcL ͉ species identification L arge-scale standardized sequencing of the mitochondrial gene CO1 has made DNA barcoding an efficient species identification tool in many animal groups (1). In plants, however, low substitution rates of mitochondrial DNA have led to the search for alternative barcoding regions. From initial investigations of plastid regions (2-4), 7 leading candidates have emerged (5, 6). Four are portions of coding genes (matK, rbcL, rpoB, and rpoC1), and 3 are noncoding spacers (atpF-atpH, trnH-psbA, and psbK-psbI). Different research groups have proposed various combinations of these loci as their preferred plant barcodes, but no consensus has emerged (5-12). This lack of an agreed standard has impeded progress in plant barcoding.Our aim here is to identify a standard DNA barcode for land plants. To achieve this goal, we have pooled data across laboratories including sequence data from 907 samples, representing 445 angiosperm, 38 gymnosperm, and 67 cryptogam species. Using various subsets of these data, we evaluated the 7 candidate loci using criteria in the Consortium for the Barcode of Life's (CBOL) data standards and guidelines for locus selection (http:// www.barcoding.si.edu/protocols.html). Universality: Which loci can be routinely sequenced across the land plants? Sequence quality and coverage: Which loci are most amenable to the production of bidirectional sequences with few or no ambiguous base calls? Discrimination: Which loci enable most species to be distinguished? ResultsUniversality. Direct universality assessments using a single primer pair for each locus in angiosperms resulted in 90%-98% PCR and sequencing success for 6/7 regions. Success for the seventh region, psbK-psbI, was 77% (Fig. 1A). Greater problems were encountered in other land plant groups, with rpoB, matK, atpF-atpH, and psbK-psbI all showing Ͻ50% success in gymnosperms and/or cryptogams based on data compiled from several laboratories (Fig. 1 A).Sequence Quality. Evaluation of sequence quality and coverage from the candidate loci demonstrated that high quality bidirectional sequences were routinely obtained from rbcL, rpoC1, and rpoB (Fig. 1B, x axis). The remaining 4 loci required more manual editing and produced f...

Background: The goal of DNA barcoding is to develop a species-specific sequence library for all eukaryotes. A 650 bp fragment of the cytochrome c oxidase 1 (CO1) gene has been used successfully for species-level identification in several animal groups. It may be difficult in practice, however, to retrieve a 650 bp fragment from archival specimens, (because of DNA degradation) or from environmental samples (where universal primers are needed).

SignificanceIn this study, we provide insight into the mechanism of effector recognition by plant nucleotide-binding domain and leucine-rich repeat proteins (NLRs), a ubiquitous class of immune receptors that plays a central role in crop protection. By structural and functional analysis of a complex between a fungal effector and an integrated decoy domain (ID) from a rice NLR, we demonstrate the importance of IDs in effector recognition and generate crucial knowledge for future engineering of NLRs to expand their recognition specificities. In addition, we propose, as a hypothesis regarding the diversity of fungal effectors, that in structurally conserved effector families, the molecular mechanisms of host target protein-binding are conserved but not the host target proteins themselves.

The accidental introduction of Caulerpa taxifolia into the Mediterranean is no longer under dispute. What has eluded researchers until now, is definitive evidence for the original, biogeographical source population. Here we present two independent lines of evidence that support an Australian origin for the Mediterranean populations of C. taxifolia. First, we reanalysed algal rDNA-internal transcribed spacer (rDNA-ITS) sequences, combining previously published sequences from different studies with 22 new sequences. The ITS sequence comparison showed that the Australian sample is the sister group of the Mediterranean-aquarium clade. Second, cloned bacterial 16S rDNA gene sequences were analysed from the associated microflora of C. taxifolia collected from Australia, Tahiti, the Philippines and the Mediterranean. Five bacterial lineages were identified, of which three were dominant. Alpha Proteobacteria were the most abundant and were found in all samples. In contrast, members of the beta Proteobacterial line and Cytophaga-Flexibacter-Bacteroides line (CFB) were mainly associated with Mediterranean and Australian samples. Frequency distributions of the five bacterial lineages were significantly different among biogeographical locations. Phylogenetic analyses of the 54 bacterial sequences derived from the four C. taxifolia individuals resulted in a well-resolved tree with high bootstrap support. The topologies of the beta Proteobacteria and CFB mirror the geographical sources of their algal hosts. Bacterial-algal associations provide an identification tool that may have wide application for the detection of marine invasions.

Understanding how fungi specialize on their plant host is crucial for developing sustainable disease control. A traditional, centuries-old rice agro-system of the Yuanyang terraces was used as a model to show that virulence effectors of the rice blast fungus Magnaporthe oryzaeh play a key role in its specialization on locally grown indica or japonica local rice subspecies. Our results have indicated that major differences in several components of basal immunity and effector-triggered immunity of the japonica and indica rice varieties are associated with specialization of M. oryzae. These differences thus play a key role in determining M. oryzae host specificity and may limit the spread of the pathogen within the Yuanyang agro-system. Specifically, the AVR-Pia effector has been identified as a possible determinant of the specialization of M. oryzae to local japonica rice.DOI: http://dx.doi.org/10.7554/eLife.19377.001

In 1984, Caulerpa taxifolia (Vahl) C. Agardh was reported along the coast of Monaco. Over the past decade it has spread along 60 km of the Mediterranean coastline and presently represents a potential risk to biodiversity. Several explanations have been advanced regarding the presence of C. taxifolia in the Mediterranean. One hypothesis maintains that the alga was introduced accidentally into the sea at Monaco, where it has been used as a decorative alga in aquaria. Caulerpa taxifolia has not been reported in earlier marine floras of the Mediterranean, and its sudden appearance has suggested that it may be a recent introduction. Another hypothesis proposes that C. taxifolia and Caulerpa mexicana Sonder ex Kützing are morphological variants of one another and hence conspecific taxa. Caulerpa mexicana has been found in the eastern Mediterranean since at least 1941. In order to establish the taxonomic identities of these taxa, individuals from five populations of C. taxifolia and four populations of C. mexicana were collected from within and outside of the Mediterranean. Comparative DNA sequence analysis of the nuclear ribosomal cistron, including the 3′‐end of the 18S, ITS1, 5.8S, and ITS2 regions, show clear phylogenetic separation of the two taxa using parsimony and maximum likelihood analyses. Separation is maintained whether the analyses are based on just the more conserved 18S data or just the fast‐ evolving spacers. The two species are thus not conspecific. For specimens of uncertain identity (i.e. taxifolia–mexicana intermediates), a PCR diagnostic amplification can easily be performed because the ITS1 in C. taxifolia is 36 nucleotides shorter than the ITS1 in C. mexicana. Whether or not C. taxifolia has been present for a longer period of time in the marine flora, either as a cryptic endemic species or as the result of one or more introductions, represents an additional hypothesis that will require identification of biogeographic populations from throughout the world, as well as a population‐level study of the Mediterranean region.

Epitrix species (Coleoptera: Chrysomelidae) feed mostly on plants from the family Solanaceae and some of them are major pests of potato crops. All Epitrix species are morphologically highly similar, which makes them difficult to identify and limits their study and management. Identification of species is mostly based on the observation of the genitalia and requires a high level of expertise. Here, we propose a tool to reliably identify all developmental stages of the most economically important Epitrix species feeding on potato in Europe and North America (Epitrix cucumeris, Epitrix similaris, Epitrix tuberis, Epitrix subcrinita and Epitrix hirtipennis). We first sequenced two DNA markers (mitochondrial cytochrome c oxidase I (COI) and nuclear internal transcribed spacer 2 (ITS2)) to test their effectiveness in differentiating among six Epitrix species (126 specimens). Morphospecies of Epitrix were well-differentiated by both DNA barcodes and no mitochondrial introgression was detected. Then, we developed an RFLP-based diagnostic method and showed that unambiguous species discrimination can be achieved by using the sole restriction enzyme TaqI on COI polymerase chain reaction products. The tool proposed here should improve our knowledge about Epitrix species biology, distribution and host range, three capacities that are particularly important in the detection and management of these pest species. Specifically, this tool should help prevent the introduction of E. tuberis and E. subcrinita in Europe and limit the spread of the recently introduced E. cucumeris and E. similaris, with minimal disruption to Solanaceae trade.

Two species complexes within the genus Xylophanes are addressed using a combination of morphological study and analysis of DNA barcode sequences. The existence of two and three cryptic species respectively within the X. loelia and X. neoptolemus complexes is revealed following consideration of both adult habitus and genital morphology, and the results of a phylogenetic analysis of partial COI sequences—DNA barcodes—for 38 specimens. The taxonomic status of the available names is discussed and to clarify and stabilize the confused nomenclature of this group, a neotype for Sphinx neoptolemus Cramer, 1780, and lectotypes for Choerocampa loelia Druce, 1878 and Chaerocampa trilineata Walker, [1865], are designated. We describe three new species: X. lolita n. sp. Vaglia and Haxaire; X. balcazari n. sp. Haxaire and Vaglia; and X. cthulhu n. sp. Haxaire and Vaglia. The first is endemic to southeastern Brazil and closely allied to X. loelia; the second two are relatives of X. neoptolemus, of which the first is known only from Guerrero and Michoacán states in Mexico while the second is widely distributed in lowland forests of Central America.