Phylogeny and molecular evolution of the DMC1 gene within the StH genome species in Triticeae (Poaceae)

Phylogeny and maternal donors of Elytrigia Desv. sensu lato (Triticeae; Poaceae) inferred from nuclear internal-transcribed spacer and trnL-F sequences

BACKGROUND

Elytrigia Desv. is a genus with a varied array of morphology, cytology, ecology, and distribution in Triticeae. Classification and systematic position of Elytrigia remain controversial. We used nuclear internal-transcribed spacer (nrITS) sequences and chloroplast trnL-F region to study the relationships of phylogenetic and maternal genome donor of Elytrigia Desv. sensu lato.

RESULTS

(1) E, F, P, St, and W genomes bear close relationship with one another and are distant from H and Ns genomes. E^e and E^b are homoeologous. (2) In ESt genome species, E genome is the origin of diploid Elytrigia species with E genome, St genome is the origin of Pseudoroegneria. (3) Diploid species Et. elongata were differentiated. (4) Et. stipifolia and Et. varnensis sequences are diverse based on nrITS data. (5) Et. lolioides contains St and H genomes and belongs to Elymus s. l. (6) E genome diploid species in Elytrigia serve as maternal donors of E genome for Et. nodosa (PI547344), Et. farcta, Et. pontica, Et. pycnantha, Et. scirpea, and Et. scythica. At least two species act as maternal donor of allopolyploids (ESt and EStP genomes).

CONCLUSIONS

Our results suggested that Elytrigia s. l. species contain different genomes, which should be divided into different genera. However, the genomes of Elytrigia species had close relationships with one another. Diploid species were differentiated, because of introgression and different geographical sources. The results also suggested that the same species and the same genomes of different species have different maternal donor. Further study of molecular biology and cytology could facilitate the evaluation of our results of phylogenetic in a more specific and accurate way.

Complete Chloroplast Genomes of Erianthus arundinaceus and Miscanthus sinensis: Comparative Genomics and Evolution of the Saccharum Complex

The genera Erianthus and Miscanthus, both members of the Saccharum complex, are of interest as potential resources for sugarcane improvement and as bioenergy crops. Recent studies have mainly focused on the conservation and use of wild accessions of these genera as breeding materials. However, the sequence data are limited, which hampers the studies of phylogenetic relationships, population structure, and evolution of these grasses. Here, we determined the complete chloroplast genome sequences of Erianthus arundinaceus and Miscanthus sinensis by using 454 GS FLX pyrosequencing and Sanger sequencing. Alignment of the E. arundinaceus and M. sinensis chloroplast genome sequences with the known sequence of Saccharum officinarum demonstrated a high degree of conservation in gene content and order. Using the data sets of 76 chloroplast protein-coding genes, we performed phylogenetic analysis in 40 taxa including E. arundinaceus and M. sinensis. Our results show that S. officinarum is more closely related to M. sinensis than to E. arundinaceus. We estimated that E. arundinaceus diverged from the subtribe Sorghinae before the divergence of Sorghum bicolor and the common ancestor of S. officinarum and M. sinensis. This is the first report of the phylogenetic and evolutionary relationships inferred from maternally inherited variation in the Saccharum complex. Our study provides an important framework for understanding the phylogenetic relatedness of the economically important genera Erianthus, Miscanthus, and Saccharum.

Rapid cloning and bioinformatic analysis of spinach Y chromosome-specific EST sequences

The genome of spinach single chromosome complement is about 1000 Mbp, which is the model material to study the molecular mechanisms of plant sex differentiation. The cytological study showed that the biggest spinach chromosome (chromosome 1) was taken as spinach sex chromosome. It had three alleles of sex-related X,X(m) and Y. Many researchers have been trying to clone the sex-determining genes and investigated the molecular mechanism of spinach sex differentiation. However,there are no successful cloned reports about these genes. A new technology combining chromosome microdissection with hybridization-specific amplification (HSA) was adopted. The spinach Y chromosome degenerate oligonucleotide primed-PCR (DOP-PCR) products were hybridized with cDNA of the male spinach flowers in florescence. The female spinach genome was taken as blocker and cDNA library specifically expressed in Y chromosome was constructed. Moreover, expressed sequence tag (EST) sequences in cDNA library were cloned, sequenced and bioinformatics was analysed. There were 63 valid EST sequences obtained in this study. The fragment size was between 53 and 486 bp. BLASTn homologous alignment indicated that 12 EST sequences had homologous sequences of nucleic acids, the rest were new sequences. BLASTx homologous alignment indicated that 16 EST sequences had homologous protein-encoding nucleic acid sequence. The spinach Y chromosome-specific EST sequences laid the foundation for cloning the functional genes, specifically expressed in spinach Y chromosome. Meanwhile, the establishment of the technology system in the research provided a reference for rapid cloning of other biological sex chromosome-specific EST sequences.

Phylogeny and differentiation of the St genome in Elymus L. sensu lato (Triticeae; Poaceae) based on one nuclear DNA and two chloroplast genes

BACKGROUND

Hybridization and polyploidization can be major mechanisms for plant evolution and speciation. Thus, the process of polyploidization and evolutionary history of polyploids is of widespread interest. The species in Elymus L. sensu lato are allopolyploids that share a common St genome from Pseudoroegneria in different combinations with H, Y, P, and W genomes. But how the St genome evolved in the Elymus s. l. during the hybridization and polyploidization events remains unclear. We used nuclear and chloroplast DNA-based phylogenetic analyses to shed some light on this process.

RESULTS

The Maximum likelihood (ML) tree based on nuclear ribosomal internal transcribed spacer region (nrITS) data showed that the Pseudoroegneria, Hordeum and Agropyron species served as the St, H and P genome diploid ancestors, respectively, for the Elymus s. l. polyploids. The ML tree for the chloroplast genes (matK and the intergenic region of trnH-psbA) suggests that the Pseudoroegneria served as the maternal donor of the St genome for Elymus s. l. Furthermore, it suggested that Pseudoroegneria species from Central Asia and Europe were more ancient than those from North America. The molecular evolution in the St genome appeared to be non-random following the polyploidy event with a departure from the equilibrium neutral model due to a genetic bottleneck caused by recent polyploidization.

CONCLUSION

Our results suggest the ancient common maternal ancestral genome in Elymus s. l. is the St genome from Pseudoroegneria. The evolutionary differentiation of the St genome in Elymus s. l. after rise of this group may have multiple causes, including hybridization and polyploidization. They also suggest that E. tangutorum should be treated as C. dahurica var. tangutorum, and E. breviaristatus should be transferred into Campeiostachys. We hypothesized that the Elymus s. l. species origined in Central Asia and Europe, then spread to North America. Further study of intraspecific variation may help us evaluate our phylogenetic results in greater detail and with more certainty.

Phylogeny and molecular evolution of the Acc1 gene within the StH genome species in Triticeae (Poaceae)

To estimate the phylogeny and molecular evolution of a single-copy gene encoding plastid acetyl-CoA carboxylase (Acc1) within the StH genome species, two Acc1 homoeologous sequences were isolated from nearly all the sampled StH genome species and were analyzed with those from 35 diploid taxa representing 19 basic genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that (1) the StH genome species from the same areas or neighboring geographic regions are closely related to each other; (2) the Acc1 gene sequences of the StH genome species from North America and Eurasia are evolutionarily distinct; (3) Dasypyrum has contributed to the nuclear genome of Elymus repens and Elymus mutabilis; (4) the StH genome polyploids have higher levels of sequence diversity in the H genome homoeolog than the St genome homoeolog; and (5) the Acc1 sequence may evolve faster in the polyploid species than in the diploids. Our result provides some insight on evolutionary dynamics of duplicate Acc1 gene, the polyploidy speciation and phylogeny of the StH genome species.