Hou-Yang Kang

Phylogeny and evolutionary history of Leymus(Triticeae; Poaceae) based on a single-copy nuclear gene encoding plastid acetyl-CoA carboxylase

BackgroundSingle- and low- copy genes are less likely subject to concerted evolution, thus making themselves ideal tools for studying the origin and evolution of polyploid taxa. Leymus is a polyploid genus with a diverse array of morphology, ecology and distribution in Triticeae. The genomic constitution of Leymus was assigned as NsXm, where Ns was presumed to be originated from Psathyrostachys, while Xm represented a genome of unknown origin. In addition, little is known about the evolutionary history of Leymus. Here, we investigate the phylogenetic relationship, genome donor, and evolutionary history of Leymus based on a single-copy nuclear Acc1 gene.ResultsTwo homoeologues of the Acc1 gene were isolated from nearly all the sampled Leymus species using allele-specific primer and were analyzed with those from 35 diploid taxa representing 18 basic genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that (1) Leymus is closely related to Psathyrostachys, Agropyron, and Eremopyrum; (2) Psathyrostachys juncea is an ancestral Ns-genome donor of Leymus species; (3) the Xm genome in Leymus may be originated from an ancestral lineage of Agropyron and Eremopyrum triticeum; (4) the Acc1 sequences of Leymus species from the Qinghai-Tibetan plateau are evolutionarily distinct; (5) North America Leymus species might originate from colonization via the Bering land bridge; (6) Leymus originated about 11-12MYA in Eurasia, and adaptive radiation might have occurred in Leymus during the period of 3.7-4.3 MYA and 1.7-2.1 MYA.ConclusionLeymus species have allopolyploid origin. It is hypothesized that the adaptive radiation of Leymus species might have been triggered by the recent upliftings of the Qinghai-Tibetan plateau and subsequent climatic oscillations. Adaptive radiation may have promoted the rapid speciation, as well as the fixation of unique morphological characters in Leymus. Our results shed new light on our understanding of the origin of Xm genome, the polyploidization events and evolutionary history of Leymus that could account for the rich diversity and ecological adaptation of Leymus species.

Introgression of Chromosome 3Ns from Psathyrostachys huashanica into Wheat Specifying Resistance to Stripe Rust

Wheat stripe rust is a destructive disease in the cool and humid wheat-growing areas of the world. Finding diverse sources of stripe rust resistance is critical for increasing genetic diversity of resistance for wheat breeding programs. Stripe rust resistance was identified in the alien species Psathyrostachys huashanica, and a wheat- P. huashanica amphiploid line (PHW-SA) with stripe rust resistance was reported previously. In this study, a P. huashanica 3Ns monosomic addition line (PW11) with superior resistance to stripe rust was developed, which was derived from the cross between PHW-SA and wheat J-11. We evaluated the alien introgressions PW11-2, PW11-5 and PW11-8 which were derived from line PW11 for reaction to new Pst race CYR32, and used molecular and cytogenetic tools to characterize these lines. The introgressions were remarkably resistant to CYR32, suggesting that the resistance to stripe rust of the introgressions thus was controlled by gene(s) located on P. huashanica chromosome 3Ns. All derived lines were cytologically stable in term of meiotic chromosome behavior. Two 3Ns chromosomes of P. huashanica were detected in the disomic addition line PW11-2. Chromosomes 1B of substitution line PW11-5 had been replaced by a pair of P. huashanica 3Ns chromosomes. In PW11-8, a small terminal segment from P. huashanica chromosome arm 3NsS was translocated to the terminal region of wheat chromosomes 3BL. Thus, this translocated chromosome is designated T3BL-3NsS. These conclusions were further confirmed by SSR analyses. Two 3Ns-specific markers Xgwm181 and Xgwm161 will be useful to rapidly identify and trace the translocated fragments. These introgressions, which had significant characteristics of resistance to stripe rust, could be utilized as novel germplasms for wheat breeding.

Phylogenetic relationships between Hystrix and its closely related genera (Triticeae; Poaceae) based on nuclear Acc1, DMC1 and chloroplast trnL-F sequences.

To estimate the phylogenetic relationship of polyploid Hystrix in Triticeae, two single-copy nuclear genes (Acc1 and DMC1) and chloroplast trnL-F sequences of six Hystrix taxa were analyzed with those of nine Leymus species (NsXm), four Elymus species (StH) and 13 diploid taxa from seven monogenomic genera. Phylogenetic analyses reveal that Hystrix taxa contain two distinct types of genome constitution, despite the overall morphological and ecological similarity among Hystrix taxa. One type of genome constitution is StH (Hy. patula) as Elymus, the other is NsXm (Hy. californica, Hy. coreana, Hy. duthiei, Hy. duthiei ssp. longearistata and Hy. komarovii) as Leymus. The St, H and Ns genomes in Hystrix are donated by Pseudoroegneria, Hordeum and Psathyrostachys, respectively. The donor of the Xm genome is closely related to Agropyron (P). The trnL-F data especially indicate that there has been a maternal haplotype polymorphism in Hystrix species. Based on these results, we suggest that Hy. coreana, Hy. duthiei, Hy. duthiei ssp. longearistata, Hy. komarovii and Hy. californica should be included in the genus Leymus, and Hy. patula in the genus Elymus.

Evolutionary dynamics of the Pgk1 gene in the polyploid genus Kengyilia (Triticeae: Poaceae) and its diploid relatives.

The level and pattern of nucleotide variation in duplicate gene provide important information on the evolutionary history of polyploids and divergent process between homoeologous loci within lineages. Kengyilia is a group of allohexaploid species with the StYP genomic constitutions in the wheat tribe. To investigate the evolutionary dynamics of the Pgk1 gene in Kengyilia and its diploid relatives, three copies of Pgk1 homoeologues were isolated from all sampled hexaploid Kengyilia species and analyzed with the Pgk1 sequences from 47 diploid taxa representing 18 basic genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that (1) Kengyilia species from the Central Asia and the Qinghai-Tibetan plateau have independent origins with geographically differentiated P genome donors and diverged levels of nucleotide diversity at Pgk1 locus; (2) a relatively long-time sweep event has allowed the Pgk1 gene within Agropyron to adapt to cold climate triggered by the recent uplifts of the Qinghai-Tibetan Plateau; (3) sweep event and population expansion might result in the difference in the dN/dS value of the Pgk1 gene in allopatric Agropyron populations, and this difference may be genetically transmitted to Kengyilia lineages via independent polyploidization events; (4) an 83 bp MITE element insertion has shaped the Pgk1 loci in the P genome lineage with different geographical regions; (5) the St and P genomes in Kengyilia were donated by Pseudoroegneria and Agropyron, respectively, and the Y genome is closely related to the Xp genome of Peridictyon sanctum. The interplay of evolutionary forces involving diverged natural selection, population expansion, and transposable events in geographically differentiated P genome donors could attribute to geographical differentiation of Kengyilia species via independent origins.

Phylogenetic relationships and Y genome origin in Elymus L. sensu lato (Triticeae; Poaceae) based on single-copy nuclear Acc1 and Pgk1 gene sequences.

To estimate the origin and genomic relationships of the polyploid species within Elymus L. sensu lato, two unlinked single-copy nuclear gene (Acc1 and Pgk1) sequences of eighteen tetraploids (StH and StY genomes) and fourteen hexaploids (StStH, StYP, StYH, and StYW genomes) were analyzed with those of 35 diploid taxa representing 18 basic genomes in Triticeae. Sequence and phylogenetic analysis suggested that: (1) the St, H, W, and P genomes were donated by Pseudoroegneria, Hordeum, Australopyrum, and Agropyron, respectively, while the Y genome is closely related to the Xp genome in Peridictyon sanctum; (2) different hexaploid Elymus s.l. species may derived their StY genome from different StY genome tetraploid species via independent origins; (3) due to incomplete lineage sorting and/or hybridization events, the genealogical conflict between the two gene trees suggest introgression involving some Elymus s.l. species, Pseudoroegneria, Agropyron and Aegilops/Triticum; (4) it is reasonable to recognize the StH genome species as Elymus sensu stricto, the StY genome species as Roegneria, the StYW genome species as Anthosachne, the StYH genome species as Campeiostachys, and the StYP genome species as Kengyilia. The occurrence of multiple origin and introgression could account for the rich diversity and ecological adaptation of Elymus s.l. species.

Molecular cytogenetic characterization of the amphiploid between bread wheat and Psathyrostachys huashanica.

A new wheat-Psathyrostachys huashanica amphiploid, PHW-SA, was characterized using molecular cytological tools to evaluate the potential utilization of P. huashanica for wheat improvement. PHW-SA pollen mother cells (PMCs) regularly revealed averagely 0.57 univalents, 24.51 ring bivalents, 3.19 rod bivalents and 0.01 trivalents per cell. Complete homologous chromosome pairing was seen in 81% of the PMCs, indicating a degree of cytological stability. P. huashanica C-banding karyotypes of PHW-SA displayed strong heterochromatin terminal bands at either or both ends. 24 P. huashanica chromosome arms showed telomeric bands. Using P. huashanica DNA as a probe and J-11 DNA as blocker, distinctive P. huashanica chromosomes, which were presented entirely greenish-yellow hybridization signals, were observed in a somatic metaphase of PHW-SA. GISH also revealed the chromosomal breakage and translocation occurring in the amphiploid PHW-SA, which may represent a centromeric fusion between P. huashanica and wheat chromosomes. Seeds storage proteins electrophoresis indicated that PHW-SA expressed some of P. huashanica specific gliadin and glutenin bands, and a few gliadin and glutenin bands of the parents disappeared and new bands appeared. The results indicated that the amphiploid PHW-SA could serve as novel germplasm sources for wheat improvement.

Development and characterization of wheat- Psathyrostachys huashanica partial amphiploids for resistance to stripe rust

Two partial amphiploid lines, B113 (32 plants) and B21 (13 plants), derived from a wheat-Psathyrostachys huashanica intergeneric cross were characterized by Giemsa C-banding and SDS-PAGE and evaluated for stripe rust resistance. All 15 partial amphiploid plants were aneuploids with either 50 (8 plants), 51 (6 plants) or 54 (1 plant) chromosomes. Some showed regular meiosis and all the P. huashanica chromosomes were included, although not in a single plant. Of 45 plants 34 showed specific bands on SDS-PAGE representing high molecular weight glutenin subunit (HMW-GS) and 41 had bands representing P. huashanica low molecular weight glutenin subunit (LMW-GS), including two new subunits. All 45 plants were highly resistant (10) or immune (35) to stripe rust mixed races CYR-30, CYR-31, Shuiyuan 7 and Shuiyuan 14. These amphiploid plants could be useful germplasm for enhancing stripe rust resistance and might improve wheat grain quality.

Effect of exogenous salicylic acid on manganese toxicity, mineral nutrients translocation and antioxidative system in polish wheat (Triticum polonicum L.)

The present study investigated the morphological and physiological effect of salicylic acid (SA) on manganese toxicity in dwarf polish wheat (Triticum polonicum L.) seedlings grown hydroponically. Our findings showed that Mn stress could decrease plant growth, cause serious chlorosis and injury the photosynthetic apparatus. An increase of Mn accumulation and the inhibition of the K and Ca absorption and the Mg, Fe and Zn translocation were observed under Mn stress. Also, there was a considerable increase in H2O2 and TBARS (thiobarbituric acid-reactive substances) content in both the roots and leaves under Mn condition. The combination of SA and Mn treatment decreased the transport of Mn, Fe and Zn from roots to shoots and increased the Ca absorption and Mg translocation. In antioxidant system, such as CAT, APX, GR, DHAR, GSH and AsA, the combined treatment significantly increased the antioxidant content and antioxidative enzyme activities compared to the Mn stress alone. The level of ROS and lipid peroxidation significantly decreased under the combination of SA and Mn. These results suggested that SA-induced Mn tolerances in polish wheat are mainly by inhibiting Mn translocation, enhancing enzymatic activities and nonenzymatic antioxidants contents, and regulating nutrient absorption and distribution in plants.

Evolutionary pattern of rDNA following polyploidy in Leymus (Triticeae: Poaceae).

Ribosomal ITS polymorphism and its ancestral genome origin of polyploid Leymus were examined to infer the evolutionary outcome of rDNA gene following allopolyploid speciation and to elucidate the geographic pattern of ITS variation. The results demonstrated that different polyploids have experienced varying fates, including maintenance or homogenization of divergent arrays, occurrence of chimeric repeats and potential pseudogenes. Our data suggested that (1) the Ns, P/F, and St genomic types in Leymus were originated from Psathyrostachys, Agropyron/Eremopyrum, and Pseudoroegneria, respectively; (2) the occurrence of a higher proportion of Leymus species with predominant uniparental rDNA type might associate with the segmental allopolyploid origin, nucleolar dominance of alloploids, and rapid radiation of Leymus; (3) maintenance of multiple parental ITS types in allopolyploid might result from long generation times associated to vegetative multiplication, number and chromosomal location of ribosomal loci and/or recurrent hybridization; (4) the rDNA genealogical structure of Leymus species might associate with the geographic origins; and (5) ITS sequence clade shared by Leymus species from Central Asia, North America, and Nordic might be an outcome of ancestral ITS homogenization. Our results shed new light on understanding evolutionary outcomes of rDNA following allopolyploid speciation and geographic isolation.

Phylogenetic relationships in Leymus (Triticeae; Poaceae): Evidence from chloroplast trnH-psbA and mitochondrial coxII intron sequences

Leymus Hochst. is a polyploid genus with a diverse array of morphology, cytology, ecology, and distribution in Triticeae. To investigate the phylogenetic relationships and maternal genome donor of polyploid Leymus, the chloroplast trnH‐psbA region and mitochondrial coxII intron sequences of 33 Leymus taxa were analyzed with those of 36 diploid perennial species representing 19 basic genomes in Triticeae. The results showed that reticulate evolution occurred in Leymus species, with the cytoplasmic lineage of Leymus contributed by different progenitors. Interspecific relationships of Leymus were also elucidated on the basis of orthologous comparison. Our data suggested that: (i) due to incomplete lineage sorting and/or difference in the pattern of chloroplast and mitochondrial inheritance, the genealogical conflict between the two genealogical patterns suggest the contribution of Psathyrostachys Nevski, Agropyron J. Gaertn, Eremopyrum (Ledeb.) Jaub. & Spach, Pseudoroegneria (Nevski) Á. Löve, Thinopyrum Á. Löve, and Lophopyrum (Host) Á. Löve to the cytoplasmic lineage of Leymus; (ii) there is a close relationship among Leymus species from the same area or neighboring geographic regions; (iii) L. coreanus (Honda) K. B. Jensen & R. R.‐C. Wang, L. duthiei (Stapf) Y. H. Zhou & H. Q. Zhang ex C. Yen, J. L. Yang & B. R. Baum, L. duthiei var. longearistatus (Hack.) Y. H. Zhou & H. Q. Zhang ex C. Yen, J. L. Yang & B. R. Baum, and L. komarovii (Roshev.) C. Yen, J. L. Yang & B. R. Baum are closely related to other Leymus species, and it is reasonable to transfer these species from the genus Hystrix Moench to Leymus; (iv) Leymus species from North America are closely related to L. coreanus from the Russian Far East and L. komarovii from northeast China but are evolutionarily distinct from Leymus species from Central Asia and the Qinghai–Tibet Plateau. The occurrence of multiple origin and introgression could account for the rich diversity and ecological adaptation of Leymus species.