The starch properties of the storage root (SR) affect the quality of sweet potato (Ipomoea batatas (L.) Lam.). Although numerous studies have analyzed the accumulation and properties of starch in sweet potato SRs, the transcriptomic variation associated with starch properties in SR has not been quantified. In this study, we measured the starch and sugar contents and analyzed the transcriptome profiles of SRs harvested from sweet potatoes with high, medium, and extremely low starch contents, at five developmental stages [65, 80, 95, 110, and 125 days after transplanting (DAP)]. We found that differences in both water content and starch accumulation in the dry matter affect the starch content of SRs in different sweet potato genotypes. Based on transcriptome sequencing data, we assembled 112336 unigenes, and identified several differentially expressed genes (DEGs) involved in starch and sucrose metabolism, and revealed the transcriptional regulatory network controlling starch and sucrose metabolism in sweet potato SRs. Correlation analysis between expression patterns and starch and sugar contents suggested that the sugar–starch conversion steps catalyzed by sucrose synthase (SuSy) and UDP-glucose pyrophosphorylase (UGPase) may be essential for starch accumulation in the dry matter of SRs, and IbβFRUCT2, a vacuolar acid invertase, might also be a key regulator of starch content in the SRs. Our results provide valuable resources for future investigations aimed at deciphering the molecular mechanisms determining the starch properties of sweet potato SRs.

Temperature and water potential are two important environmental factors influencing germination and subsequent seedling establishment. Seed germination requirements vary with species and with the environment in which the seeds are produced. Stipa species dominate large areas of the Eurasian zonal vegetation, but comparisons of germination requirements between Stipa species from different habitats is limited. We investigated the effects of temperature and water potential on seed germination of S. grandis , S. purpurea , and S. penicillata from habitats with low temperatures and relatively abundant rainfall (cool habitats) and S. glareosa , S. breviflora , S. gobiea , and S. bungeana from habitats with relatively high temperatures and low amount of rainfall (warm habitats). Seeds of species from cool habitats had a higher base ( T b ), optimal ( T o ), and maximum ( T c ) temperature than those of species from warm habitats, except for the base temperature of S. purpurea . Response of six tested Stipa species to water potential differed among species but not between habitats. Median water potential for germination was lowest for S. bungeana , S. penicillata , and S. gobiea . There was a negative correlation between hydrotime constant ( θ H ) and base water potential for 50% of the seeds of all species to germinate ( ψ b(50) ). Germination time of seven Stipa species in response to temperature and water was well predicted by thermal time and hydrotime models. Results of the present study on germination of these seven species of Stipa may provide useful suggestions for grassland restoration in different habitats.

Melilotus is one of the most important legume forages, but the lack of molecular markers has limited the development and utilization of Melilotus germplasm resources. In the present study, 151 M clean reads were generated from various genotypes of Melilotus albus using Illumina sequencing. A total of 19,263 potential EST-SSRs were identified from 104,358 unigene sequences. Moreover, 18,182 primer pairs were successfully designed, and 550 primer pairs were selected using criteria of base repeat type, fragment length and annealing temperature. In addition, 550 primer pairs were screened by using PCR amplification products and used to assess polymorphisms in 15 M. albus accessions. A total of 114 primer pairs were detected as being highly polymorphic, and the average polymorphism information content (PIC) value was 0.79. Furthermore, those 114 polymorphic primer pairs were used to evaluate the transferability to 18 species of the genus Melilotus, and 70 EST-SSR markers were found to be transferable among the 18 Melilotus species. According to the UPGMA dendrogram and STRUCTURE analysis, the 18 Melilotus species were classified into three clusters. This study offers a valuable resource for the genetic diversity and molecular assisted breeding of germplasm resources in the genus Melilotus.

Sweet potato (Ipomoea batatas L.) is a nutritious food crop and, based on the high starch content of its storage root, a potential bioethanol feedstock. Enhancing the nutritional value and starch quantity of storage roots are important goals of sweet potato breeding programs aimed at developing improved varieties for direct consumption, processing, and industrial uses. However, developing improved lines of sweet potato is challenging due to the genetic complexity of this plant and the lack of genome information. Short sequence repeat (SSR) markers are powerful molecular tools for tracking important loci in crops and for molecular-based breeding strategies; however, few SSR markers and marker-trait associations have hitherto been identified in sweet potato. In this study, we identified 1824 SSRs by using a de novo assembly of publicly available ESTs and mRNAs in sweet potato, and designed 1476 primer pairs based on SSR-containing sequences. We mapped 214 pairs of primers in a natural population comprised of 239 germplasms, and identified 1278 alleles with an average of 5.972 alleles per locus and a major allele frequency of 0.7702. Population structure analysis revealed two subpopulations in this panel of germplasms, and phenotypic characterization demonstrated that this panel is suitable for association mapping of starch-related traits. We identified 32, 16, and 17 SSR markers associated with starch content, β-carotene content, and starch composition in the storage root, respectively, using association analysis and further evaluation of a subset of sweet potato genotypes with various characteristics. The SSR markers identified here can be used to select varieties with desired traits and to investigate the genetic mechanism underlying starch and carotenoid formation in the starchy roots of sweet potato.

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Melilotus comprises 19 species, while the phylogenetic relationships between species remain unclear. In the present work, three chloroplast genes, rbcL, matK, trnL-F, and one nuclear region, ITS (internal transcribed spacer) belonging to 48 populations of 18 species of Melilotus were sequenced and phylogenetic trees were constructed to study their interspecific relationships. Based on the phylogenetic tree generated in this study using rbcL analysis, the Melilotus genus is clearly monophyletic in the legume family. Both Bayesian and maximum-parsimony approaches were used to analyze the data. The nrDNA ITS provided more informative characteristics (9.8%) than cpDNA (3.0%). Melilotus contains two closely related groups, clade I and clade II. M. spicatus, M. indicus and M. segetalis have a close relationship. M. infestus, M. siculus and M. sulcatus are closely related. The comparing between molecular phylogeny and flower color classification in Melilotus showed that the flower color is not much informative for phylogenetics of this genus.

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Coumarin and its derivatives are widely used as fragrances in industrial products and have medical value. The goal of the present study was to discover genes and pathways related to coumarin biosynthesis in Melilotus albus using transcriptome analysis. The genes of five M. albus near-isogenic lines (NILs) that had different coumarin content and β-glucosidase activity according to the investigation of pedigree were quantified and then analysed by RNA-Seq. Using transcriptome analysis, differentially expressed genes (DEGs) were identified in two pairwise comparisons that differed in coumarin content as well as in two pairwise comparisons that differed in β-glucosidase activity. Gene expression pattern analysis suggested similar transcriptional trends in the genotypes with the same coumarin levels. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) database of DEGs was used to identify functional pathways associated with coumarin biosynthesis. We identified 111 unigenes, with several DEGs among them possibly being related to coumarin synthesis pathways. Unigenes encoding a hexokinase, an abscisic acid receptor, a phenylalanine ammonia-lyase (PAL) and two peroxidases particularly showed correspondence with the coumarin content of different genotypes. These results will contribute to a better understanding of the coumarin biosynthesis in M. albus.