Abstract
In Japan, two Eutrema species, wasabi (Eutrema japonicum, the important traditional Japanese condiment) and yuriwasabi (E. tenue), have been recognized as endemic species. We sequenced complete chloroplast (cp) genomes of seven wasabi and yuriwasabi accessions from Japan to study their phylogeny and evolution, using molecular dating of species divergence. Phylogenetic analyses of the complete cp DNA of these two Japanese species and five other Eurasian Eutrema species revealed that wasabi and yuriwasabi did not form a monophyletic group. One yuriwasabi accession (Gifu) formed a clade with E. yunnanense from China, indicating that this accession should be considered as a different species from the other yuriwasabi accessions. We reveal that Japanese Eutrema species diverged from the ‘E. yunnanense–yuriwasabi (Gifu)’ clade approximately 1.3 million years ago (Mya), suggesting that the connection between Japan and the Eurasian continent has existed more recently than the Quaternary period. The abundance of cp sequence data in this study also allowed the detection of genetic differentiation among wasabi cultivars. The two polymorphic sites detected between ‘Fujidaruma’ and ‘Shimane No.3’ were used to develop genotyping markers. The cp genome information provided here will thus inform the evolutionary histories of Japanese Eutrema species and help in genotyping wasabi cultivars.
Highlights
Wasabi (Japanese horseradish: Eutrema japonicum (Miq.) Koidz., syn
The whole cp genomes of the Eutrema species found in Japan were 153,604–153,875 bp long, including the long single copy section (LSC) of 83,879–84,046 bp, the short single copy section (SSC) of 17,715–17,856 bp and a pair of inverted repeats (IRs) of 25,972–26,034 bp each (Supplemental Table S1 and Fig. 1)
The results showed a close relationship among these three species and revealed polyphyly of E. tenue
Summary
Wasabi (Japanese horseradish: Eutrema japonicum (Miq.) Koidz., syn. Wasabia japonica (Miq.) Matsum.) is a perennial herb that plays an important role in Japanese cuisine and culture. To obtain a comprehensive understanding of the evolutionary relationships and speciation process, we used the Illumina sequencing system to obtain the whole cp genome sequence of the wasabi cultivar, ‘Fujidaruma’, and the Sanger sequencing method to obtain the whole cp genome sequences of four Japanese accessions of E. japonicum and two Japanese accessions of E. tenue These accessions cover the geographic distribution of the species in Japan. Increased knowledge of Eutrema genetic and phenotypic diversity will help to accelerate the breeding of wasabi but will provide a better understanding of its complex evolutionary process This is important in times of global warming to which many plant species are responding by shifting their distribution to different latitudes
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