Chloroplast DNA variation in diploid and polyploid species of Bromus (Poaceae) subgenera Festucaria and Ceratochloa

A phylogenetic analysis of Bromus (Poaceae: Pooideae: Bromeae) based on nuclear ribosomal and plastid data, with a focus on Bromus sect. Bromus

To investigate phylogenetic relationships among and within major lineages of Bromus, with focus on Bromus sect. Bromus, we analyzed DNA sequences from two nuclear ribosomal (ITS, ETS) and two plastid (rpl32-trnL_UAG , matK) regions. We sampled 103 ingroup accessions representing 26 taxa of B. section Bromus and 15 species of other Bromus sections. Our analyses confirm the monophyly of Bromus s.l. and identify incongruence between nuclear ribosomal and plastid data partitions for relationships within and among major Bromus lineages. Results support classification of B. pumilio and B. gracillimus within B. sect. Boissiera and B. sect. Nevskiella, respectively. These species are sister groups and are closely related to B. densus (B. sect. Mexibromus) in nrDNA trees and Bromus sect. Ceratochloa in plastid trees. Bromus sect. Bromopsis is paraphyletic. In nrDNA trees, species of Bromus sects. Bromopsis, Ceratochloa, Neobromus, and Genea plus B. rechingeri of B. sect. Bromus form a clade, in which B. tomentellus is sister to a B. sect. Genea-B. rechingeri clade. In the plastid trees, by contrast, B. sect. Bromopsis species except B. tomentosus form a clade, and B. tomentosus is sister to a clade comprising B. sect. Bromus and B. sect. Genea species. Affinities of B. gedrosianus, B. pulchellus, and B. rechingeri (members of the B. pectinatus complex), as well as B. oxyodon and B. sewerzowii, are discordant between nrDNA and plastid trees. We infer these species may have obtained their plastomes via chloroplast capture from species of B. sect. Bromus and B. sect. Genea. Within B. sect. Bromus, B. alopecuros subsp. caroli-henrici, a clade comprising B. hordeaceus and B. interruptus, and B. scoparius are successive sister groups to the rest of the section in the nrDNA phylogeny. Most relationships among the remaining species of B. sect. Bromus are unresolved in the nrDNA and plastid trees. Given these results, we infer that most B. sect. Bromus species likely diversified relatively recently. None of the subdivisional taxa proposed for Bromus sect. Bromus over the last century correspond to natural groups identified in our phylogenetic analyses except for a group including B. hordeaceus and B. interruptus.

Comparative chloroplast genomes: insights into the evolution of the chloroplast genome of Camellia sinensis and the phylogeny of Camellia

BACKGROUND

Chloroplast genome resources can provide useful information for the evolution of plant species. Tea plant (Camellia sinensis) is among the most economically valuable member of Camellia. Here, we determined the chloroplast genome of the first natural triploid Chinary type tea ('Wuyi narcissus' cultivar of Camellia sinensis var. sinensis, CWN) and conducted the genome comparison with the diploid Chinary type tea (Camellia sinensis var. sinensis, CSS) and two types of diploid Assamica type teas (Camellia sinensis var. assamica: Chinese Assamica type tea, CSA and Indian Assamica type tea, CIA). Further, the evolutionary mechanism of the chloroplast genome of Camellia sinensis and the relationships of Camellia species based on chloroplast genome were discussed.

RESULTS

Comparative analysis showed the evolutionary dynamics of chloroplast genome of Camellia sinensis were the repeats and insertion-deletions (indels), and distribution of the repeats, indels and substitutions were significantly correlated. Chinese tea and Indian tea had significant differences in the structural characteristic and the codon usage of the chloroplast genome. Analysis of sequence characterized amplified region (SCAR) using sequences of the intergenic spacers (trnE/trnT) showed none of 292 different Camellia sinensis cultivars had similar sequence characteristic to triploid CWN, but the other four Camellia species did. Estimations of the divergence time showed that CIA diverged from the common ancestor of two Assamica type teas about 6.2 Mya (CI: 4.4-8.1 Mya). CSS and CSA diverged to each other about 0.8 Mya (CI: 0.4-1.5 Mya). Moreover, phylogenetic clustering was not exactly consistent with the current taxonomy of Camellia.

CONCLUSIONS

The repeat-induced and indel-induced mutations were two important dynamics contributed to the diversification of the chloroplast genome in Camellia sinensis, which were not mutually exclusive. Chinese tea and Indian tea might have undergone different selection pressures. Chloroplast transfer occurred during the polyploid evolution in Camellia sinensis. In addition, our results supported the three different domestication origins of Chinary type tea, Chinese Assamica type tea and Indian Assamica type tea. And, the current classification of some Camellia species might need to be further discussed.

The study of inter-specific relationships of Bromus genus based on SCoT and ISSR molecular markers

The genus of Bromus is one of the most important collection of rangeland plants, which are distributed in a wide range of natural areas of Iran. Interspecific relationships were evaluated in 90 accessions of 18 Bromus species based on 15 ISSR and 15 SCoT primers. SCoT markers separated the accessions better than ISSR marker. In addition, there was a high interspecific diversity between surveying germplasm. The sections of Bromus genus completely separated based on DNA molecular markers. SCoT markers could separate the accessions in each species. The primers of SC₅ and SC₃₅ from SCoT marker and UBC861, UBC857 and UBC844 primers from ISSR marker were identified as the best primers in revealing of genetic diversity between accessions. The sections of Ceratochloa, Genea, Pnigma and Bromus were monophyletic and were placed in one cluster. The section Bromus had a direct relationship with section Genea. In other words, section Ceratochloa has a direct relationship with Pnigma. B. tectorum and B. sericeus. B. sterilis had the most distance with other species in section Genea. B. squarrosus and B. japonicus had the most similarity and B. briziformis with B. danthoniae and B. scoparius with B. rechingeri had a moderate relationship in section Bromus. B. tomentosus and B. persicus had the highest similarity and B. riparius with B. biebersteinii and B. tomentellus with B. inermis had a moderate similarity in section Pnigma.

Elucidating polyploidization of bermudagrasses as assessed by organelle and nuclear DNA markers

Clarification of relationships among ploidy series of Cynodon accessions could be beneficial to bermudagrass breeding programs, and would enhance our understanding of the evolutionary biology of this warm season grass species. This study was initiated to elucidate polyploidization among Cynodon accessions with different ploidy series collected from Turkey based on chloroplast and nuclear DNA. Forty Cynodon accessions including 7 diploids, 3 triploids, 10 tetraploids, 11 pentaploids, and 9 hexaploids were analyzed using chloroplast DNA restriction fragment-length polymorphism (cpDNA RFLP), chloroplast DNA simple sequence repeat (cpDNA SSR), and nuclear DNA markers based on neighbor-joining (NJ) and principle component analyses (PCA). All three-marker systems with two statistical algorithms clustered the diploids apart from the other ploidy levels. Assuming autopolyploidy, spontaneous polyploidization followed by rapid diversification among the higher ploidy levels than the diploids is likely in Cynodon's evolution. Few tetraploid and hexaploid accessions were clustered with or closely to the group of diploids, supporting the hypothesis above. Eleven haplotypes as estimated by cpDNA RFLP and SSR markers were detected. This study indicated that the diploids had different organelle genome from the rest of the ploidy series and provided valuable insight into relationships among ploidy series of Cynodon accessions based on cp and nuclear DNAs.

Chloroplast genome organization of bromegrass, Bromus inermis Leyss

A physical map of the Bromus inermis chloroplast genome was constructed using heterologous probes of barley and wheat chloroplast DNA (cpDNA) to locate restriction sites. The map was aligned from data obtained from filter hybridization experiments on single and double enzyme digests. Cleavage sites for the enzymes PstI, SalI, KpnI, XhoI and PvuII were mapped. The chloroplast genome of B. inermis is similar in physical organization to that of other grasses. The circular cpDNA molecule of B. inermis has the typical small (12.8 kbp) and large (81.3 kbp) single-copy regions separated by a pair of inverted repeat (21 kbp) regions. The cpDNA molecule of B. inermis is collinear in sequence to that of wheat, rye, barley and oats. No structural rearrangements or major deletions were observed, indicating that the cpDNA of Bromus is a useful tool in phylogenetic studies.