Transcriptome Sequence Reveals Candidate Genes Involving in the Post-Harvest Hardening of Trifoliate Yam Dioscorea dumetorum.

Storage ability of trifoliate yam (Dioscorea dumetorum) is restricted by a severe post-harvest hardening (PHH) phenomenon, which starts within the first 24 h after harvest and renders tubers inedible. Previous work has only focused on the biochemical changes affecting PHH in D. dumetorum. To the best of our knowledge, the candidate genes responsible for the hardening of D. dumetorum have not been identified. Here, transcriptome analyses of D. dumetorum tubers were performed in yam tubers of four developmental stages: 4 months after emergence (4MAE), immediately after harvest (AH), 3 days after harvest (3DAH) and 14 days after harvest (14DAH) of four accessions (Bangou 1, Bayangam 2, Fonkouankem 1, and Ibo sweet 3) using RNA-Seq. In total, between AH and 3DAH, 165, 199, 128 and 61 differentially expressed genes (DEGs) were detected in Bayangam 2, Fonkouankem 1, Bangou 1 and Ibo sweet 3, respectively. Functional analysis of DEGs revealed that genes encoding for CELLULOSE SYNTHASE A (CESA), XYLAN O-ACETYLTRANSFERASE (XOAT), CHLOROPHYLL A/B BINDING PROTEIN1, 2, 3, 4 (LHCB1, LHCB2, LHCB3, and LCH4) and an MYB transcription factor were predominantly and significantly up-regulated 3DAH, implying that these genes were potentially involved in the PHH as confirmed by qRT-PCR. A hypothetical mechanism of this phenomenon and its regulation has been proposed. These findings provide the first comprehensive insights into gene expression in yam tubers after harvest and valuable information for molecular breeding against the PHH.

Comparative Phylogeography of Veronica spicata and V. longifolia (Plantaginaceae) Across Europe: Integrating Hybridization and Polyploidy in Phylogeography.

Climatic fluctuations in the Pleistocene caused glacial expansion-contraction cycles in Eurasia and other parts of the world. Consequences of these cycles, such as population expansion and subsequent subdivision, have been studied in many taxa at intraspecific population level across much of the Northern Hemisphere. However, the consequences for the potential of hybridization and polyploidization are poorly understood. Here, we investigated the phylogeographic structure of two widespread, closely related species, Veronica spicata and Veronica longifolia, across their European distribution ranges. We assessed the extent and the geographic pattern of polyploidization in both species and hybridization between them. We used genome-scale SNP data to clarify phylogenetic relationships and detect possible hybridization/introgression events. In addition, crossing experiments were performed in different combination between V. spicata and V. longifolia individuals of two ploidy levels and of different geographic origins. Finally, we employed ecological niche modeling to infer macroclimatic differences between both species and both ploidy levels. We found a clear genetic structure reflecting the geographical distribution patterns in both species, with V. spicata showing higher genetic differentiation than V. longifolia. We retrieved significant signals of hybridization and introgression in natural populations from the genetic data and corroborated this with crossing experiments. However, there were no clear phylogeographic patterns and unequivocal macroclimatic niche differences between diploid and tetraploid lineages. This favors the hypothesis, that autopolyploidization has happened frequently and in different regions. The crossing experiments produced viable hybrids when the crosses were made between plants of the same ploidy levels but not in the interploidy crosses. The results suggest that hybridization occurs across the overlapping areas of natural distribution ranges of both species, with apparently directional introgression from V. spicata to V. longifolia. Nevertheless, the two species maintain their species-level separation due to their adaptation to different habitats and spatial isolation rather than reproductive isolation.

Genetic diversity and population structure of trifoliate yam (Dioscorea dumetorum Kunth) in Cameroon revealed by genotyping-by-sequencing (GBS).

BACKGROUND: Yams (Dioscorea spp.) are economically important food for millions of people in the humid and sub-humid tropics. Dioscorea dumetorum (Kunth) is the most nutritious among the eight-yam species, commonly grown and consumed in West and Central Africa. Despite these qualities, the storage ability of D. dumetorum is restricted by severe postharvest hardening of the tubers that can be addressed through concerted breeding efforts. The first step of any breeding program is bound to the study of genetic diversity. In this study, we used the Genotyping-By-Sequencing of Single Nucleotide Polymorphism (GBS-SNP) to investigate the genetic diversity and population structure of 44 accessions of D. dumetorum in Cameroon. Ploidy was inferred using flow cytometry and gbs2ploidy. RESULTS: We obtained on average 6371 loci having at least information for 75% accessions. Based on 6457 unlinked SNPs, our results demonstrate that D. dumetorum is structured into four populations. We clearly identified, a western/north-western, a western, and south-western populations, suggesting that altitude and farmers-consumers preference are the decisive factors for differential adaptation and separation of these populations. Bayesian and neighbor-joining clustering detected the highest genetic variability in D. dumetorum accessions from the south-western region. This variation is likely due to larger breeding efforts in the region as shown by gene flow between D. dumetorum accessions from the south-western region inferred by maximum likelihood. Ploidy analysis revealed diploid and triploid levels in D. dumetorum accessions with mostly diploid accessions (77%). Male and female accessions were mostly triploid (75%) and diploid (69%), respectively. The 1C genome size values of D. dumetorum accessions were on average 0.333 ± 0.009 pg and 0.519 ± 0.004 pg for diploids and triploids, respectively. CONCLUSIONS: Germplasm characterization, population structure and ploidy are an essential basic information in a breeding program as well as for conservation of intraspecific diversity. Thus, results obtained in this study provide valuable information for the improvement and conservation of D. dumetorum. Moreover, GBS appears as an efficient powerful tool to detect intraspecific variation.

Transcriptomic resources and marker validation for diploid and polyploid Veronica (Plantaginaceae) from New Zealand and Europe.

PREMISE OF THE STUDY: Polyploidy may generate novel variation, leading to adaptation and species diversification. An excellent natural system to study polyploid evolution in a comparative framework is Veronica (Plantaginaceae), which comprises several parallel, recently evolved polyploid series. METHODS: Over 105 million Illumina paired-end sequence reads were generated from cDNA libraries of leaf tissue from eight individuals representing three European and four New Zealand species. Forty-eight simple sequence repeat (SSR) and 48 low-copy nuclear (LCN) markers were developed and validated with Fluidigm microfluidic PCR and Illumina MiSeq amplicon sequencing on 48 different individuals each. RESULTS: Individual Trinity assemblies were similar regarding annotated transcripts (13,009-14,271), mean contig length (635-742 bp), N50 value (916-1133 bp), E90N50 value (1099-1308 bp), contigs with positive BLAST hits (42-63%), and gene ontology terms. Analyses of 29,738 single-nucleotide polymorphisms (8746 phylogenetically informative) mined from these transcriptomes plus two outgroups (Picrorhiza kurrooa and Plantago ovata) showed moderate to high bootstrap support for all branches and reticulation among sampled European Veronica. DISCUSSION: The transcriptome sequences themselves, as well as the validated SSR (40/48) and LCN (11/48) markers derived from them, show inter- and intraspecific genetic variation. These resources will be invaluable for future population genetic, phylogenetic, and functional genetic investigations in polyploid Veronica.

Characterization of 12 polymorphic SSR markers in Veronica subsect. Pentasepalae (Plantaginaceae) and cross-amplification in 10 other subgenera.

PREMISE OF THE STUDY: Microsatellite primers were developed in the perennial herbs of the diploid-polyploid complex Veronica subsect. Pentasepalae (Plantaginaceae) to investigate the role that hybridization has played in the evolution of the group, which includes several endangered species. METHODS AND RESULTS: Twelve pairs of primers leading to polymorphic and readable markers were identified and optimized from V. jacquinii and V. orbiculata using a microsatellite-enriched library method and 454 GS-FLX technique. The set of primers amplified dinucleotide to pentanucleotide repeats, and the number of alleles per locus ranged from one to six, one to 11, and one to nine for V. orsiniana, V. javalambrensis, and V. rosea, respectively. Transferability analyses were performed in 20 species corresponding to 10 different subgenera. CONCLUSIONS: These results indicate the utility of the newly developed microsatellites across Veronica subsect. Pentasepalae, which will help in the study of gene flow patterns and genetic structure.

Supratidal Extremophiles--Cyanobacterial Diversity in the Rock Pools of the Croatian Adria.

Hardly any molecular studies have been done on euendoliths of marine coastal environments, especially along the supratidal ranges of carbonate coasts. In our study, we provide a comparative sequence analysis using 454 pyrosequencing of the 16S ribosomal RNA (rRNA) gene combined with extensive microscopy of the endolithic community from rock pools of the Croatian Adria. Molecular diversity indices and richness estimates showed high level of diversity, particularly in high-salinity samples. The most common cyanobacteria belong to the order Pleurocapsales, similar to observations on limestone coasts in other parts of the world. Using single-cell amplification sequences of Hormathonema spp., Hyella caespitosa, and Kyrtuthrix dalmatica was for the first time introduced to the public GenBank.Microscopic investigations did not show qualitative variances in diversity among sites with different salinity but clear differences in prevalent organisms from similar environments suggesting that most of them are adapted to inhabit extreme, marine endolithic habitats and that similar species inhabit geographically separated but ecologically similar environments. This is a remarkable concordance rather seldom seen in molecular community studies in support of the hypothesis that endolithic ecosystems are seeded from a global meta-community.The relative diversity of the community is greater than those described from harsh endolithic habitats of cold and hot deserts. The maximum likelihood phylogenetic tree consisting of 166 operational taxonomic units (OTUs) at 96 % sequence similarity revealed 11 distinct clusters. Three clusters contained only epilithic or endolithic taxa, and five clusters contained mixed epilithic and endolithic taxa. Organisms clustered according to their taxonomic affiliations and not to their preferences to salt concentrations.