Genetic relationships in a germplasm collection of Camellia japonica and Camellia oleifera using SSR analysis.

Camellia japonica produces different color and bigger flowers, widely being used for gardening green in southern China. However, cultivars were introduced from different regions, but their origin and pedigree information is either not available poorly documented, causing problems in authentication. Many low-yield trees in Camellia oleifera forests have been used as stocks for grafting C. japonica. However, the survival rate of grafts between these two species is related to genetic relationship between stock of C. oleifera and scion of C. japonica. We used simple sequence repeat (SSR) markers to genotype 41 C. japonica cultivars from different regions, as well as nine genotypes of C. oleifera in China. Twenty-one SSR markers generated 438 alleles, with an average of 20.85 alleles per locus. All alleles were used to generate Dice coefficients between two genotypes of all genotypes of these two species. Cluster analysis based on SSR data clustered genotypes showed clustering of genotypes into groups that agreed well with their taxonomic classification and geographic origin. Cultivar 'Damaonao' was a large tree with flowers of composite color, and showed the most genetic distance from other C. japonica cultivars and C. oleifera genotypes in the cluster analysis. The cultivars of C. japonica are distinct from genotypes of C. oleifera. The results for cultivars of C. japonica also revealed the presence of different cultivars with the same name, and identical cultivars but with a different name. SSR profiles can improve C. japonica germplasm management, and provide potential determine correlations between genetic relationship and graft compatibility among scions of C. japonica and genotypes of C. oleifera.

Development and cross-species transferability of unigene-derived microsatellite markers in an edible oil woody plant, Camellia oleifera (Theaceae).

Camellia oleifera is an important edible oil woody plant in China. Lack of useful molecular markers hinders current genetic research on this tree species. Transcriptome sequencing of developing C. oleifera seeds generated 69,798 unigenes. A total of 6949 putative microsatellites were discovered among 6042 SSR-containing unigenes. Then, 150 simple sequence repeats (SSRs) were evaluated in 20 varieties of C. oleifera. Of these, 52 SSRs revealed polymorphism, with the number of alleles per locus ranging from 2 to 15 and expected heterozygosity values from 0.269 to 0.888. The polymorphic information content varied from 0.32 to 0.897. Cross-species transferability rates in Camellia chekangoleosa and Camellia japonica were 90.4 and 78.8%, respectively. The 52 polymorphic unigene-derived SSR markers serve to enrich existing microsatellite marker resources for C. oleifera and offer potential for applications in genetic diversity evaluation, molecular fingerprinting, and genetic mapping in C. oleifera, C. chekangoleosa, and C. japonica.

Transcriptomic analysis of Camellia ptilophylla and identification of genes associated with flavonoid and caffeine biosynthesis.

Camellia ptilophylla, or cocoa tea, is naturally decaffeinated and its predominant catechins and purine alkaloids are trans-catechins and theobromine Regular tea [Camellia sinensis (L.) O. Ktze.] is evolutionarily close to cocoa tea and produces cis-catechins and caffeine. Here, the transcriptome of C. ptilophylla was sequenced using the 101-bp paired-end technique. The quality of the raw data was assessed to yield 70,227,953 cleaned reads totaling 7.09 Gbp, which were assembled de novo into 56,695 unique transcripts and then clustered into 44,749 unigenes. In catechin biosynthesis, leucoanthocyanidin reductase (LAR) catalyzes the transition of leucoanthocyanidin to trans-catechins, while anthocyanidin synthase (ANS) and anthocyanidin reductase (ANR) catalyze cis-catechin production. Our data demonstrate that two LAR genes (CpLAR1 and CpLAR2) by C. ptilophylla may be advantageous due to the combined effects of this quantitative trait, permitting increased leucoanthocyanidin consumption for the synthesis of trans-catechins. In contrast, the only ANS gene observed in C. sinensis (CsANS) shared high identity (99.2%) to one homolog from C. ptilophylla (CpANS1), but lower identity (~80%) to another (CpANS2). We hypothesized that the diverged CpANS2 might have lost its ability to synthesize cis-catechins. C. ptilophylla and C. sinensis each contain two copies of ANR, which share high identity and may share the same function. Transcriptomic sequencing captured two N-methyl nucleosidase genes named NMT1 and NMT2. NMT2 was highly identical to three orthologous genes TCS2, PCS2, and ICS2, which did not undergo methylation in vitro; in contrast, NMT1 was less identical to TCS, PCS and ICS, indicating that NMT1 may undergo neofunctionalization.

Genetic diversity and differentiation in Camellia reticulata (Theaceae) polyploid complex revealed by ISSR and ploidy.

Camellia reticulata is a well-known ornamental and oil plant that is endemic to southwest China. This species shows three cell ploidies, i.e., diploidy, tetraploidy and hexaploidy. We made the first investigation of genetic diversity and differentiation of natural populations of C. reticulata, and 114 individuals from 6 populations were sampled. Cytogeography results showed that ploidy is invariable within populations and evenly distributed. A relatively high level of genetic diversity was found in C. reticulata, both at the species level (PPB = 88.89%; H = 0.2809; I = 0.4278) and at the population level (mean PPB = 42.13%; mean H = 0.14; mean I = 0.21). We found a relatively low degree of differentiation among ploidies (G(ST) = 0.2384; AMOVA = 10.26%) and a relatively high degree of differentiation among populations (G(CS) = 0.3807; AMOVA = 48.75%). The high genetic diversity can be explained by its biological character, wide distribution and ploidies, and the special genetic structure can be ascribed to polyploid origin from hybridization with different Camellia spp. This information will be useful for the introduction, conservation and further studies of C. reticulata and related species.