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, 8 (4), e62574

Phylogenetic Relationships of Citrus and Its Relatives Based on matK Gene Sequences

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Phylogenetic Relationships of Citrus and Its Relatives Based on matK Gene Sequences

Tshering Penjor et al. PLoS One.

Abstract

The genus Citrus includes mandarin, orange, lemon, grapefruit and lime, which have high economic and nutritional value. The family Rutaceae can be divided into 7 subfamilies, including Aurantioideae. The genus Citrus belongs to the subfamily Aurantioideae. In this study, we sequenced the chloroplast matK genes of 135 accessions from 22 genera of Aurantioideae and analyzed them phylogenetically. Our study includes many accessions that have not been examined in other studies. The subfamily Aurantioideae has been classified into 2 tribes, Clauseneae and Citreae, and our current molecular analysis clearly discriminate Citreae from Clauseneae by using only 1 chloroplast DNA sequence. Our study confirms previous observations on the molecular phylogeny of Aurantioideae in many aspects. However, we have provided novel information on these genetic relationships. For example, inconsistent with the previous observation, and consistent with our preliminary study using the chloroplast rbcL genes, our analysis showed that Feroniella oblata is not nested in Citrus species and is closely related with Feronia limonia. Furthermore, we have shown that Murraya paniculata is similar to Merrillia caloxylon and is dissimilar to Murraya koenigii. We found that "true citrus fruit trees" could be divided into 2 subclusters. One subcluster included Citrus, Fortunella, and Poncirus, while the other cluster included Microcitrus and Eremocitrus. Compared to previous studies, our current study is the most extensive phylogenetic study of Citrus species since it includes 93 accessions. The results indicate that Citrus species can be classified into 3 clusters: a citron cluster, a pummelo cluster, and a mandarin cluster. Although most mandarin accessions belonged to the mandarin cluster, we found some exceptions. We also obtained the information on the genetic background of various species of acid citrus grown in Japan. Because the genus Citrus contains many important accessions, we have comprehensively discussed the classification of this genus.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Maximum likelihood tree of the matK genes from accessions belonged to Aurantioideae.
Numbers at the nodes indicate bootstrap values (% over 1,000 replicates).
Figure 2
Figure 2. Neighbor-joining tree of the matK genes from accessions belonged to Aurantioideae.
Numbers at the nodes indicate bootstrap values (% over 1,000 replicates).
Figure 3
Figure 3. Photographs of Feronia limonia and Feroniella oblata leaves.
Figure 4
Figure 4. Photographs of Merrillia caloxylon, Murraya paniculata, and Murraya koenigii leaves.
Figure 5
Figure 5. Maximum likelihood tree of the matK genes from accessions belonged to “true citrus fruit trees.”
Numbers at the nodes indicate bootstrap values (% over 1,000 replicates). Numbers in parenthesis indicate the number of accessions. Citrus depressa z contains 6 accessions (Kaachi, Mikanguwa, Shiikunin, Shiikuribu, Ishikunibu, and Okitsu strains). Citrus depressa y contains 2 accessions (Fusubuta and Kabishi).
Figure 6
Figure 6. Neighbor-joining tree of the matK genes from accessions belonged to “true citrus fruit trees.”
Numbers at the nodes indicate bootstrap values (% over 1,000 replicates). Numbers in parenthesis indicates the number of accessions. Citrus depressa z contains 6 accessions (Kaachi, Mikanguwa, Shiikunin, Shiikuribu, Ishikunibu, and Okitsu strains). Citrus depressa y contains 2 accessions (Fusubuta and Kabishi).

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References

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Publication types

Grant support

Part of this work was supported by a Grant-in-Aid for Challenging Exploratory Research from the Japan Society for the Promotion of Science. No additional external funding was received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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