Peanut (Arachis hypogaea) is an autogamous allotetraploid legume (2n = 4x = 40) that is widely cultivated as a food and oil crop. More than 6,000 DNA markers have been developed in Arachis spp., but high-density linkage maps useful for genetics, genomics, and breeding have not been constructed due to extremely low genetic diversity. Polymorphic marker loci are useful for the construction of such high-density linkage maps. The present study used in silico analysis to develop simple sequence repeat-based and transposon-based markers.

Tomato (Solanum lycopersicum) is regarded as a model plant of the Solanaceae family. The genome sequencing of the tomato cultivar ‘Heinz 1706’ was recently completed. To accelerate the progress of tomato genomics studies, systematic bioresources, such as mutagenized lines and full-length cDNA libraries, have been established for the cultivar ‘Micro-Tom’. However, these resources cannot be utilized to their full potential without the completion of the genome sequencing of ‘Micro-Tom’. We undertook the genome sequencing of ‘Micro-Tom’ and here report the identification of single nucleotide polymorphisms (SNPs) and insertion/deletions (indels) between ‘Micro-Tom’ and ‘Heinz 1706’. The analysis demonstrated the presence of 1.23 million SNPs and 0.19 million indels between the two cultivars. The density of SNPs and indels was high in chromosomes 2, 5 and 11, but was low in chromosomes 6, 8 and 10. Three known mutations of ‘Micro-Tom’ were localized on chromosomal regions where the density of SNPs and indels was low, which was consistent with the fact that these mutations were relatively new and introgressed into ‘Micro-Tom’ during the breeding of this cultivar. We also report SNP analysis for two ‘Micro-Tom’ varieties that have been maintained independently in Japan and France, both of which have served as standard lines for ‘Micro-Tom’ mutant collections. Approximately 28,000 SNPs were identified between these two ‘Micro-Tom’ lines. These results provide high-resolution DNA polymorphic information on ‘Micro-Tom’ and represent a valuable contribution to the ‘Micro-Tom’-based genomics resources.

Cuscuta spp. are obligate parasites that connect to host vascular tissue using a haustorium. In addition to water, nutrients, and metabolites, a large number of mRNAs are bidirectionally exchanged between Cuscuta spp. and their hosts. This trans-specific movement of mRNAs raises questions about whether these molecules function in the recipient species. To address the possibility that mobile mRNAs are ultimately translated, we built upon recent studies that demonstrate a role for transfer RNA (tRNA)-like structures (TLSs) in enhancing mRNA systemic movement. C. campestris was grown on Arabidopsis that expressed a β-glucuronidase (GUS) reporter transgene either alone or in GUS-tRNA fusions. Histochemical staining revealed localization in tissue of C. campestris grown on Arabidopsis with GUS-tRNA fusions, but not in C. campestris grown on Arabidopsis with GUS alone. This corresponded with detection of GUS transcripts in Cuscuta on Arabidopsis with GUS-tRNA, but not in C. campestris on Arabidopsis with GUS alone. Similar results were obtained with Arabidopsis host plants expressing the same constructs containing an endoplasmic reticulum localization signal. In C. campestris, GUS activity was localized in the companion cells or phloem parenchyma cells adjacent to sieve tubes. We conclude that host-derived GUS mRNAs are translated in C. campestris and that the TLS fusion enhances RNA mobility in the host-parasite interactions.

The genus Cuscuta is a group of parasitic plants that are distributed world-wide. The process of parasitization starts with a Cuscuta plant coiling around the host stem. The parasite’s haustorial organs then establish a vascular connection allowing for access to the phloem content. The host and the parasite form new cellular connections, suggesting coordination of developmental and biochemical processes. Simultaneous monitoring of gene expression in the parasite’s and host’s tissues may shed light on the complex events occurring between the parasitic and host cells and may help to overcome experimental limitations (i.e. how to separate host tissue from Cuscuta tissue at the haustorial connection). A novel approach is to use bioinformatic analysis to classify sequencing reads as either belonging to the host or to the parasite and to characterize the expression patterns. Owing to the lack of a comprehensive genomic dataset from Cuscuta spp., such a classification has not been performed previously. We first classified RNA-Seq reads from an interface region between the non-model parasitic plant Cuscuta japonica and the non-model host plant Impatiens balsamina. Without established reference sequences, we classified reads as originating from either of the plants by stepwise similarity search against de novo assembled transcript sets of C. japonica and I. balsamina, unigene sets of the same genus, and cDNA sequences of the same family. We then assembled de novo transcriptomes from the classified read sets. We assessed the quality of the classification by mapping reads to contigs of both plants, achieving a misclassification rate low enough (0.22-0.39%) to be used reliably for differential gene expression analysis. Finally, we applied our read classification method to RNA-Seq data from the interface between the non-model parasitic plant C. japonica and the model host plant Glycine max. Analysis of gene expression profiles at 5 parasitizing stages revealed differentially expressed genes from both C. japonica and G. max, and uncovered the coordination of cellular processes between the two plants. We demonstrated that reliable identification of differentially expressed transcripts in undissected interface region of the parasite-host association is feasible and informative with respect to differential-expression patterns.

Parasitic plants exchange various types of RNAs with their host plants, including mRNA, and small non-coding RNA. Among small non-coding RNAs, miRNA production is known to be induced at the haustorial interface. The induced miRNAs transfer to the host plant and activate secondary siRNA production to silence target genes in the host. In addition to interfacial transfer, long-distance movement of the small RNAs has also been known to mediate signaling and regulate biological processes. In this study, we tested the long-distance movement of trans-species small RNAs in a parasitic-plant complex. Small RNA-Seq was performed using a complex of a stem parasitic plant, Cuscuta campestris, and a host, Arabidopsis thaliana. In the host plant’s parasitized stem, genes involved in the production of secondary siRNA, AtSGS3 and AtRDR6, were upregulated, and 22-nt small RNA was enriched concomitantly, suggesting the activation of secondary siRNA production. Stem-loop RT-PCR and subsequent sequencing experimentally confirmed the mobility of the small RNAs. Trans-species mobile small RNAs were detected in the parasitic interface and also in distant organs. To clarify the mode of long-distance translocation, we examined whether C. campestris-derived small RNA moves long distances in A. thaliana sgs3 and rdr6 mutants or not. Mobility of C. campestris-derived small RNA in sgs3 and rdr6 mutants suggested the occurrence of direct long-distance transport without secondary siRNA production in the recipient plant.

Stem parasitic plants (Cuscuta spp.) develop a specialized organ called a haustorium to penetrate their hosts’ stem tissues. To reach the vascular tissues of the host plant, the haustorium needs to overcome the physical barrier of the cell wall, and the parasite–host interaction via the cell wall is a critical process. However, the cell wall components responsible for the establishment of parasitic connections have not yet been identified. In this study, we investigated the spatial distribution patterns of cell wall components at a parasitic interface using parasite–host complexes of Cuscuta campestris–Arabidopsis thaliana and Cuscuta japonica–Glycine max. We focused on arabinogalactan proteins (AGPs), because AGPs accumulate in the cell walls of searching hyphae of both C. campestris and C. japonica. We found more AGPs in elongated haustoria than in pre haustoria, indicating that AGP accumulation is developmentally regulated. Using in situ hybridization, we identified five genes in C. campestris that encode hyphal-expressed AGPs that belong to the fasciclin-like AGP (FLA) family, which were named CcFLA genes. Three of the five CcFLA genes were expressed in the holdfast, which develops on the Cuscuta stem epidermis at the attachment site for the host’s stem epidermis. Our results suggest that AGPs are involved in hyphal elongation and adhesion to host cells, and in the adhesion between the epidermal tissues of Cuscuta and its host.