Development of Polymorphic Genic SSR Markers by Transcriptome Sequencing in the Welsh Onion (Allium fistulosum L.)

Omics approaches in Allium research: Progress and way ahead

BACKGROUND

The genus Allium (Family: Amaryllidaceae) is an economically important group of crops cultivated worldwide for their use as a vegetable and spices. Alliums are also well known for their nutraceutical properties. Among alliums, onion, garlic, leek, and chives cultivated worldwide. Despite their substantial economic and medicinal importance, the genome sequence of any of the Allium is not available, probably due to their large genome sizes. Recently evolved omics technologies are highly efficient and robust in elucidating molecular mechanisms of several complex life processes in plants. Omics technologies, such as genomics, transcriptomics, proteomics, metabolomics, metagenomics, etc. have the potential to open new avenues in research and improvement of allium crops where genome sequence information is limited. A significant amount of data has been generated using these technologies for various Allium species; it will help in understanding the key traits in Allium crops such as flowering, bulb development, flavonoid biosynthesis, male sterility and stress tolerance at molecular and metabolite level. This information will ultimately assist us in speeding up the breeding in Allium crops.

METHOD

In the present review, major omics approaches, and their progress, as well as potential applications in Allium crops, could be discussed in detail.

RESULTS

Here, we have discussed the recent progress made in Allium research using omics technologies such as genomics, transcriptomics, micro RNAs, proteomics, metabolomics, and metagenomics. These omics interventions have been used in alliums for marker discovery, the study of the biotic and abiotic stress response, male sterility, organ development, flavonoid and bulb color, micro RNA discovery, and microbiome associated with Allium crops. Further, we also emphasized the integrated use of these omics platforms for a better understanding of the complex molecular mechanisms to speed up the breeding programs for better cultivars.

CONCLUSION

All the information and literature provided in the present review throws light on the progress and potential of omics platforms in the research of Allium crops. We also mentioned a few research areas in Allium crops that need to be explored using omics technologies to get more insight. Overall, alliums are an under-studied group of plants, and thus, there is tremendous scope and need for research in Allium species.

Microsatellite analysis and marker development in garlic: distribution in EST sequence, genetic diversity analysis, and marker transferability across Alliaceae

Allium vegetables, such as garlic and onion, have understudied genomes and limited molecular resources, hindering advances in genetic research and breeding of these species. In this study, we characterized and compared the simple sequence repeats (SSR) landscape in the transcriptomes of garlic and related Allium (A. cepa, A. fistulosum, and A. tuberosum) and non-Allium monocot species. In addition, 110 SSR markers were developed from garlic ESTs, and they were characterized-along with 112 previously developed SSRs-at various levels, including transferability across Alliaceae species, and their usefulness for genetic diversity analysis. Among the Allium species analyzed, garlic ESTs had the highest overall SSR density, the lowest frequency of trinucleotides, and the highest of di- and tetranucleotides. When compared to more distantly related monocots, outside the Asparagales order, it was evident that ESTs of Allium species shared major commonalities with regards to SSR density, frequency distribution, sequence motifs, and GC content. A significant fraction of the SSR markers were successfully transferred across Allium species, including crops for which no SSR markers have been developed yet, such as leek, shallot, chives, and elephant garlic. Diversity analysis of garlic cultivars with selected SSRs revealed 36 alleles, with 2-5 alleles/locus, and PIC = 0.38. Cluster analysis grouped the accessions according to their flowering behavior, botanical variety, and ecophysiological characteristics. Results from this study contribute to the characterization of Allium transcriptomes. The new SSR markers developed, along with the data from the polymorphism and transferability analyses, will aid in assisting genetic research and breeding in garlic and other Allium.

Development of Genome-Wide SSR Markers from Angelica gigas Nakai Using Next Generation Sequencing

Angelica gigas Nakai is an important medicinal herb, widely utilized in Asian countries especially in Korea, Japan, and China. Although it is a vital medicinal herb, the lack of sequencing data and efficient molecular markers has limited the application of a genetic approach for horticultural improvements. Simple sequence repeats (SSRs) are universally accepted molecular markers for population structure study. In this study, we found over 130,000 SSRs, ranging from di- to deca-nucleotide motifs, using the genome sequence of Manchu variety (MV) of A. gigas, derived from next generation sequencing (NGS). From the putative SSR regions identified, a total of 16,496 primer sets were successfully designed. Among them, we selected 848 SSR markers that showed polymorphism from in silico analysis and contained tri- to hexa-nucleotide motifs. We tested 36 SSR primer sets for polymorphism in 16 A. gigas accessions. The average polymorphism information content (PIC) was 0.69; the average observed heterozygosity (HO) values, and the expected heterozygosity (HE) values were 0.53 and 0.73, respectively. These newly developed SSR markers would be useful tools for molecular genetics, genotype identification, genetic mapping, molecular breeding, and studying species relationships of the Angelica genus.