This study in V. clarionifolia provides valuable tools and information, based on simple sequence repeats derived from the transcriptome, which could be extended to other valerians, and possibly more ones not included in this study.
The SSRs developed from transcriptomic libraries have a high probability to be transferred to other species of the genus, as they correspond to highly conserved regions. This feature enhances its application to species that remained molecularly unexplored.
Different levels of polymorphism present in different species can be attributed to mating system type, age of distributions, dispersal and adaptive strategies, domestication grade or natural population status. High variability can be due to the size of the data set, SSR search criteria, and mining tool used for the SSR search [37]. The proportion of transcriptome containing SSRs varies in different plant species. In an exhaustive analysis of microsatellite patterns, The distribution across eukaryotic genomes remarked the distinct patterns of microsatellite, presence and abundance in the different taxonomic groups that represent their establishment in a common ancient founding member of the group [38]. In a comprehensive analysis of SSR from 112 plant species from different plant phyla[36], the amount of SSR in Valeriana was similar founded in eucots, monocots and other higher plants (including, Gymnospermae, Gnetophyta, Bryophyta, Pteridophyta). The largest amount of SSR found in lower plants (Chlorophyta) authors attributed the need of this plants to adapt to early extreme environments.
Transferability of SSR technique has been successfully applied to agriculture crops and wild relatives. Helianthus annuus L. and rare sunflower species were compared using EST-derived SSRs [[39]]. In this last, found that these markers were more than 3 times as transferable across species as compared with anonymous SSRs (73% vs. 21%, respectively). Transferability of rice SSR was tested across the genera [40], including wheat, oat, pearl millet, soybean, sunflower and chickpea and high value for specific genomic studies like genetic diversity studies or QTL mapping and marker-trait association were proved. Microsatellite marker transferability have also been successful from Prunus across rosaceous crops almond, peach, apricot, Japanese plum, European plum, cherry, apple, pear, and strawberry [41].
In the genus Valeriana, expressed sequence tags (ESTs) and nuclear sequence information was used in V. jatamansi [27]. Those tools were integrated with other attributes to harbor maximum genetic variation within the species, to identify several populations that could be used as a promising stock for mass multiplication and can be informative for conservation purposes [42].
In our study, all SSR loci were also useful for diversity analysis. Genetic variability detected in the studied populations suggest a good chance of success on a larger scale. Even the microsatellite with lowest PIC value had private alleles which aids to discriminate populations.
The success of cross-species markers and the application in compared studies of ecology [43] were extensively reviewed. Both, the proportion of amplified and polymorphic values represent a measure of the success of the transferability. Even if they do not focus on differential mutation rates, homoplasy or evolution, the potential of cross-species transfer of these markers is high.
Since their discovery, microsatellites or SSR benefits as a molecular marker over other marker systems were recognized. SSR takes advantage of RFLP with its greater polymorphism rates, higher reproducibility compares with RADP by its high annealing temperatures and easier use over AFLP as a PCR based technique. Additionally, they can be automated, and genotype costs can be lowered combining a set of markers in a single reaction.
High costs because of laborious and time-consuming process restrained de novo development of SSR markers in the past, as point it as the main disadvantage [44]. Nowadays, the evolution of mass sequencing techniques and the availability of expression and genomic libraries databases overcome this problem. Thus, SSR appears more favourable and accessible to conduct genetic experiments in non-model plant species, as SNP requires sophisticated instrumentation for their detection and validation.
This is the first development of molecular markers based on transcriptomic data in native valerians from Patagonia. The development of genomic tools will allow us the authentication, selection, and the tracking in multiplication cycles to produce selected “top” clones. Also, will contribute to the selection and maintenance of specific genotypes/chemo types.
In this way, we can attend a severe problem of sustainability production, environmentally respectful to and product quality. Native medicinal plants could turn out in innovative crops for agriculture diversification and a promising alternative for regional economies. The use of these markers can extend to population genetic analysis and gene flow estimation of Valeriana and other related taxa.