Abstract
BackgroundAs one of the most important but seriously endangered wild relatives of the cultivated tea, Camellia taliensis harbors valuable gene resources for tea tree improvement in the future. The knowledge of genetic variation and population structure may provide insights into evolutionary history and germplasm conservation of the species.ResultsHere, we sampled 21 natural populations from the species' range in China and performed the phylogeography of C. taliensis by using the nuclear PAL gene fragment and chloroplast rpl32-trnL intergenic spacer. Levels of haplotype diversity and nucleotide diversity detected at rpl32-trnL (h = 0.841; π = 0.00314) were almost as high as at PAL (h = 0.836; π = 0.00417). Significant chloroplast DNA population subdivision was detected (GST = 0.988; NST = 0.989), suggesting fairly high genetic differentiation and low levels of recurrent gene flow through seeds among populations. Nested clade phylogeographic analysis of chlorotypes suggests that population genetic structure in C. taliensis has been affected by habitat fragmentation in the past. However, the detection of a moderate nrDNA population subdivision (GST = 0.222; NST = 0.301) provided the evidence of efficient pollen-mediated gene flow among populations and significant phylogeographical structure (NST > GST; P < 0.01). The analysis of PAL haplotypes indicates that phylogeographical pattern of nrDNA haplotypes might be caused by restricted gene flow with isolation by distance, which was also supported by Mantel’s test of nrDNA haplotypes (r = 0.234, P < 0.001). We found that chlorotype C1 was fixed in seven populations of Lancang River Region, implying that the Lancang River might have provided a corridor for the long-distance dispersal of the species.ConclusionsWe found that C. taliensis showed fairly high genetic differentiation resulting from restricted gene flow and habitat fragmentation. This phylogeographical study gives us deep insights into population structure of the species and conservation strategies for germplasm sampling and developing in situ conservation of natural populations.
Highlights
As one of the most important but seriously endangered wild relatives of the cultivated tea, Camellia taliensis harbors valuable gene resources for tea tree improvement in the future
In comparison to mean estimate of cpDNA diversity detected by various cpDNA markers in 170 plant species [4], our study showed that C. taliensis possessed an abundant variation in the chloroplast rpl32-trnL intergenic with cpDNA diversity (h) of 0.841
By using rpl32-trnL intergenic spacer and Phenylalanine ammonialyase (PAL) gene fragment as markers, we estimated genetic structure of C. taliensis populations across its distribution range in China. cpDNA data suggest that the differentiation among the C. taliensis populations was rather high (GST = 0.988; NST = 0.989), placing it among the surveyed plant species with the highest cpDNA differentiation [4]
Summary
As one of the most important but seriously endangered wild relatives of the cultivated tea, Camellia taliensis harbors valuable gene resources for tea tree improvement in the future. Because of its close relationship with the cultivated tea and fascinated aftertaste, C. taliensis has been consumed instead of regular tea by local people in parts of Asia, in Yunnan Province of China [13] These wild tea germplasms undoubtedly harbor abundant gene sources and possess great potentials to enhance genetic improvement of cultivated tea in the future. The well-known Pu’er tea, made from organic leaves of wild C. taliensis plants in Yunnan Province, enjoys a price 10–100 times higher than cultivated tea trees in the market. For this reason, natural populations of the species have become endangered due to over-picking driven by economic incentives. It is urgently needed to pay particular attention to making efficient germplasm conservation of C. taliensis
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