Genome-Wide Analysis of Simple Sequence Repeats in Cabbage (Brassica oleracea L.)

Cabbage (Brassica oleracea L. var. capitata) accounts for a critical vegetable crop belonging to Brassicaceae family, and it has been extensively planted worldwide. Simple sequence repeats (SSRs), the markers with high polymorphism and co-dominance degrees, offer a crucial genetic research resource. The current work identified totally 64,546 perfect and 93,724 imperfect SSR motifs in the genome of the cabbage ‘TO1000.’ Then, we divided SSRs based on the respective overall length and repeat number into different linkage groups. Later, we characterized cabbage genomes from the perspectives of motif length, motif-type classified and SSR level, and compared them across cruciferous genomes. Furthermore, a large set of 64,546 primer pairs were successfully identified, which generated altogether 1,113 SSR primers, including 916 (82.3%) exhibiting repeated and stable amplification. In addition, there were 32 informative SSR markers screened, which might decide 32 cabbage genotypes for their genetic diversity, with level of polymorphism information of 0.14–0.88. Cultivars were efficiently identified by the new strategy designating manual diagram for identifying cultivars. Lastly, 32 cabbage accessions were clearly separately by five Bol-SSR markers. Besides, we verified whether such SSRs were available and transferable in 10 Brassicaceae relatives. Based on the above findings, those genomic SSR markers identified in the present work may facilitate cabbage research, which lay a certain foundation for further gene tagging and genetic linkage analyses, like marker-assisted selection, genetic mapping, as well as comparative genomic analysis.

Development and characterization of Simple Sequence Repeats (SSRs) markers in durian kura-kura (Durio testudinarius Becc.) using NGS data

Durian Kura-kura (Durio testudinarius Becc.) belongs to the Malvaceae family and is an endemic species of Borneo. Recently, genomic-based next-generation sequencing (NGS) approaches have been carried out for germplasm conservation and plant breeding programs. The NGS technologies allow plant genomes to be sequenced quickly and inexpensively and enable the efficient development of SSR markers through the in-silico approaches. This study aimed to develop and characterize simple sequence repeats (SSRs) from the assembled genome. The 1203929 scaffolds of the assembled genome were produced from the Ray assembler. The SSRs were identified and extracted using the MISA program produced 4315 sequences containing SSRs. The six motif repeats of SSRs were identified; consist of 431 sequences of dinucleotide (the most motif is AT), 3257 sequences of trinucleotide (the most motif is TTA), 516 sequences of tetranucleotide (the most motif is AAAT), 89 sequences of pentanucleotide (the most motif is ATTTT), 18 sequences of hexanucleotide and four sequences of heptanucleotide. The new SSRs markers will be used in further studies of genetic population of D. testudinarius and plant breeding programs.

Drought Resistance Loci in Recombinant Lines of Iranian Oryza sativa L. in Germination Stage

In order to locate control genes related to Oryza sativa L. traits at the germination stage under normal conditions and at drought stress levels (−4.5 and −9.0 bar), we evaluated 120 F8 generation offspring from the cross between two cultivars Neda × Ahlemitarum in a factorial experiment in a completely randomized block design with three replications in 2013 in the botanical laboratory of Gonbad Kavous University. A linkage map was prepared using 90 Simple Sequence Repeats (SSR) markers and 28 Inter Simple Sequence Repeats (ISSR), and 6 iPBS and 9 IRAP markers (265 polymorphic alleles). The results of the analysis of variance showed that all of the evaluated traits had a significant difference at the probability level of 1%. Hence, it can be noted that the desired genetic diversity can be found between genotypes. The results of the stepwise regression analysis for the germination percentage as a dependent variable and other traits as independent variables in the studied treatments showed that under normal conditions, there was variable coleoptile length, but under drought stress of −4.5 and −9.0 bar, the variable plumule dry weight entered the model. In this study, the markers included in RM1-RM490 and ISSR2-3-RM133 of chromosomes 1 and 6 of Oryza sativa were identified as the main regulators of traits associated with Oryza sativa drought resistance. In particular, they present the quantitative trait loci (QTL) that control the first stages of germination of Oryza sativa in water stress conditions.

LegumeSSRdb: A Comprehensive Microsatellite Marker Database of Legumes for Germplasm Characterization and Crop Improvement

Microsatellites, or simple sequence repeats (SSRs), are polymorphic loci that play a major role as molecular markers for genome analysis and plant breeding. The legume SSR database is a webserver which contains simple sequence repeats (SSRs) from genomes of 13 legume species. A total of 3,706,276 SSRs are present in the database, 698,509 of which are genic SSRs, and 3,007,772 are non-genic. This webserver is an integrated tool to perform end-to-end marker selection right from generating SSRs to designing and validating primers, visualizing the results and blasting the genomic sequences at one place without juggling between several resources. The user-friendly web interface allows users to browse SSRs based on the genomic region, chromosome, motif type, repeat motif sequence, frequency of motif, and advanced searches allow users to search based on chromosome location range and length of SSR. Users can give their desired flanking region around repeat and obtain the sequence, they can explore the genes in which the SSRs are present or the genes between which the SSRs are bound design custom primers, and perform in silico validation using PCR. An SSR prediction pipeline is implemented where the user can submit their genomic sequence to generate SSRs. This webserver will be frequently updated with more species, in time. We believe that legumeSSRdb would be a useful resource for marker-assisted selection and mapping quantitative trait loci (QTLs) to practice genomic selection and improve crop health. The database can be freely accessed at http://bioinfo.usu.edu/legumeSSRdb/.

The Complete Chloroplast Genome Sequence of Four Plant Species, Their SSR Identification and Phylogenetic Analysis

The chloroplast genome is conservative and stable, which can be employed to resolve genotypes. Currently, published nuclear sequences and molecular markers failed to differentiate the species from taxa robustly, including Machilus leptophylla, Hanceola exserta, Rubus bambusarum, and Rubus henryi. In this study, the four chloroplast genomes were characterized, and then their simple sequence repeats (SSRs) and phylogenetic positions were analyzed. The results demonstrated the four chloroplast genomes consisted of 152.624 kb, 153.296kb, 156.309 kb, and 158.953 kb in length, involving 124, 130, 129, and 131 genes, respectively. Moreover, the chloroplast genomes contained typical four regions. Six classes of SSR were identified from the four chloroplast genomes, in which mononucleotide was the class with the most members. The types of the repeats were various within individual classes of SSR. Phylogenetic trees indicated that M. leptophylla was clustered with M. yunnanensis, and H. exserta was confirmed under family Ocimeae. Additionally, R. bambusarum and R. henryi were clustered together, whereas they did not belong to the same species due to the differing SSR features. This research would provide evidence for resolving the species and contributed new genetic information for further study.

A Comparative Study of the Chloroplast Genomes of Five Lepidium Medicinal Plants

Background Herb genomics is a rapidly developing field of medicinal plant research and development. Plant genomic studies demonstrate the unique advantage of employing plants in medicinal therapy. The genus Lepidium falls under the Brassicaceae family and it includes crucial medicinal plants. Herein, we sequenced the complete chloroplast (cp) genomes of Lepidium apetalum (LA) and Lepidium perfoliatum (LP) and assessed their genetic profiles against the reported profiles of Lepidium sativum (LS), Lepidium meyenii (LM), and Lepidium virginicum (LV). Results In particular, we examined genomic arrangement, gene number, type, and repeat sequences. Based on our annotation data, both LA and LP possessed 130 distinct genes that included 85 protein-coding, 37 transfer RNA (tRNA), and 8 ribosomal RNA (rRNA) genes. Our repeat analyses revealed that LA harbored 20 forward repeats, 16 palindrome repeats, 30 tandem repeats, and 87 simple sequence repeats, whereas LP had 15 forward repeats, 20 palindrome repeats,4 reverse repeats, 21 tandem repeats, and 98 simple sequence repeats. Using syntenic analysis, we also revealed a high degree of sequence similarity within the coding regions of Lepidium cp genomes and a remarkably high degree of divergence among the intergenic spacers. Pairwise alignment and single-nucleotide polymorphism (SNP) examinations further revealed certain Lepidium-specific gene fragments, particularly in the intergenic regions of the trnK-atpA, trnC-psbC, trnT-rbcL, ndhF-ndhH, ycf1-trnR, accD, ccsA, matK, ndhF, rpoB, rpoC2, and ycf1 genes. Moreover, following codon usage analysis, we observed that codon 14 was the most frequently used codon in the Lepidium CDS. In addition, correlation investigations revealed that the ENC (the effective number of codon) content was strongly associated with GC3, GC3s, and N. Conclusion Based on these data, LA and LP originate from very similar genetic backgrounds. Furthermore, neutrality, ENC, and PR2-plots analyses demonstrated that the CUB (the codon usage bias) of Lepidium cp genome was strongly influenced by mutation and natural selection. Our analysis of the cp genomic sequences of LA and LP will likely enhance breeding, species recognition, phylogenetic evolution, and cp genetic engineering of the Lepidium medicinal plants.