Genome-wide characterization of i-motifs and their potential roles in the stability and evolution of transposable elements in rice.

I-motifs (iMs) are non-canonical DNA secondary structures that fold from cytosine (C)-rich genomic DNA regions termed putative i-motif forming sequences (PiMFSs). The structure of iMs is stabilized by hemiprotonated C-C base pairs, and their functions are now suspected in key cellular processes in human cells such as genome stability and regulation of gene transcription. In plants, their biological relevance is still largely unknown. Here, we characterized PiMFSs with high potential for i-motif formation in the rice genome by developing and applying a protocol hinging on an iMab antibody-based immunoprecipitation (IP) coupled with high-throughput sequencing (seq), consequently termed iM-IP-seq. We found that PiMFSs had intrinsic subgenomic distributions, cis-regulatory functions and an intricate relationship with DNA methylation. We indeed found that the coordination of PiMFSs with DNA methylation may affect dynamics of transposable elements (TEs) among different cultivated Oryza subpopulations or during evolution of wild rice species. Collectively, our study provides first and unique insights into the biology of iMs in plants, with potential applications in plant biotechnology for improving important agronomic rice traits.

Epigenomic features of DNA G-quadruplexes and their roles in regulating rice gene transcription.

A DNA G-quadruplex (G4) is a non-canonical four-stranded nucleic acid structure involved in many biological processes in mammals. The current knowledge on plant DNA G4s, however, is limited; whether and how DNA G4s impact gene expression in plants is still largely unknown. Here, we applied a protocol referred to as BG4-DNA-IP-seq followed by a comprehensive characterization of DNA G4s in rice (Oryza sativa L.); we next integrated dG4s (experimentally detectable G4s) with existing omics data and found that dG4s exhibited differential DNA methylation between transposable element (TE) and non-TE genes. dG4 regions displayed genic-dependent enrichment of epigenomic signatures; finally, we showed that these sites displayed a positive association with expression of DNA G4-containing genes when located at promoters, and a negative association when located in the gene body, suggesting localization-dependent promotional/repressive roles of DNA G4s in regulating gene transcription. This study reveals interrelations between DNA G4s and epigenomic signatures, as well as implicates DNA G4s in modulating gene transcription in rice. Our study provides valuable resources for the functional characterization or bioengineering of some of key DNA G4s in rice.

Characterization of functional relationships of R-loops with gene transcription and epigenetic modifications in rice.

We conducted genome-wide identification of R-loops followed by integrative analyses of R-loops with relation to gene expression and epigenetic signatures in the rice genome. We found that the correlation between gene expression levels and profiled R-loop peak levels was dependent on the positions of R-loops within gene structures (hereafter named "genic position"). Both antisense only (ASO)-R-loops and sense/antisense (S/AS)-R-loops sharply peaked around transcription start sites (TSSs), and these peak levels corresponded positively with transcript levels of overlapping genes. In contrast, sense only (SO)-R-loops were generally spread over the coding regions, and their peak levels corresponded inversely to transcript levels of overlapping genes. In addition, integrative analyses of R-loop data with existing RNA-seq, chromatin immunoprecipitation sequencing (ChIP-seq), DNase I hypersensitive sites sequencing (DNase-seq), and whole-genome bisulfite sequencing (WGBS or BS-seq) data revealed interrelationships and intricate connections among R-loops, gene expression, and epigenetic signatures. Experimental validation provided evidence that the demethylation of both DNA and histone marks can influence R-loop peak levels on a genome-wide scale. This is the first study in plants that reveals novel functional aspects of R-loops, their interrelations with epigenetic methylation, and roles in transcriptional regulation.

Research progress of plant cytogenetics in Jiangsu province.

Cytogenetics was established based on the "Chromosome theory of inheritance", proposed by Boveri and Sutton and evidenced by Morgan's lab in early stage of the 20 th centrary. With rapid development of related research areas, especially molecular genetics, cytogenetics developed from traditional into a new era, molecular cytogenetics in late 1960s. Featured by an established technique named DNA in situ hybridization (ISH), molecular cytogenetics has been applied in various research areas. ISH provids vivid and straightforward figures showing the virtual presence of DNA, RNA or proteins. In combination with genomics and cell biology tools, ISH and derived techniques have been widely used in studies of the origin, evolution, domestication of human, animal and plant, as well as wide hybridization and chromosome engineering. The physical location and order of DNA sequences revealed by ISH enables the detection of chromosomal re-arrangments among related species and gaps of assembled genome sequences. In addition, ISH using RNA or protein probes can reveal the location and quantification of transcripted RNA or translated protein. Since the 1970s, scientists from universities or institutes belonging to the Jiangsu Society of Genetics have initiated cytogenetics researches using various plant species. In recent years, research platforms for molecular cytogenetics have also been well established in Nanjing Agricultural University, Yangzhou University, Nanjing Forestry University, Jiangsu Xuhuai Academy of Agricultural Sciences, and Jiangsu Normal University. The application of molecular cytogenetics in plant evolution, wide hybridization, chromosome engineering, chromosome biology, genomics has been successful. Significant progresses have been achieved, both in basic and applied researches. In this paper, we will review main research progresses of plant cytogenetics in Jiangsu province, and discuss the potential development of this research area.

Salt-Responsive Genes are Differentially Regulated at the Chromatin Levels Between Seedlings and Roots in Rice.

The elucidation of epigenetic responses of salt-responsive genes facilitates understanding of the underlying mechanisms that confer salt tolerance in rice. However, it is still largely unknown how epigenetic mechanisms are associated with the expression of salt-responsive genes in rice and other crops. In this study, we reported tissue-specific gene expression and tissue-specific changes in chromatin modifications or signatures between seedlings and roots in response to salt treatment. Our study indicated that among six of individual mark examined (H3K4me3, H3K27me3, H4K12ac, H3K9ac, H3K27ac and H3K36me3), a positive association between salt-related changes in histone marks and the expression of differentially expressed genes (DEGs) was observed only for H3K9ac and H4K12ac in seedlings and H3K36me3 in roots. In contrast, chromatin states (CSs) with combinations of six histone modification marks played crucial roles in the differential expression of salt-responsive genes between seedlings and roots. Most importantly, CS7 containing the bivalent marks H3K4me3 and H3K27me3, with a mutual exclusion of functions with each other, displayed distinct functions in the expression of DEGs in both tissues. Specifically, H3K27me3 in CS7 mainly suppressed the expression of DEGs in roots, while H3K4me3 affected the expression of down- and up-regulated genes, possibly by antagonizing the repressive role of H3K27me3 in seedlings. Our findings indicate distinct impacts of the CSs on the differential expression of salt-responsive genes between seedlings and roots in rice, which provides an important background for understanding chromatin-based epigenetic mechanisms that might confer salt tolerance in plants.

Chromatin states responsible for the regulation of differentially expressed genes under 60Co~γ ray radiation in rice.

BACKGROUND: The role of histone modifications in the DNA damage response has been extensively studied in non-plant systems, including mammals and yeast. However, there is a lack of detailed evidence showing how chromatin dynamics, either an individual mark or combined chromatin states, participate in regulating differentially expressed genes in the plant DNA damage response. RESULTS: In this study, we used RNA-seq and ChIP-seq to show that differentially expressed genes (DEGs), in response to ionizing radiation (IR), might be involved in different pathways responsible for the DNA damage response. Moreover, chromatin structures associated with promoters, exons and intergenic regions are significantly affected by IR. Most importantly, either an individual mark or a certain chromatin state was found to be highly correlated with the expression of up-regulated genes. In contrast, only the chromatin states, as opposed to any individual marks tested, are related to the expression of the down-regulated genes. CONCLUSIONS: Our findings demonstrate that IR-related DEGs are modulated by distinct epigenetic mechanisms. Either chromatin states or distinct histone dynamics may act sequentially or in combination in regulating up-regulated genes, but the complex chromatin structure is mainly responsible for the expression of down-regulated genes. Thus, this study provides new insights into how up- and down-regulated genes are epigenetically regulated at the chromatin levels, thereby helping us to understand distinct epigenetic mechanisms that function in the plant DNA damage response.

Histone modifications facilitate the coexpression of bidirectional promoters in rice.

BACKGROUND: Bidirectional gene pairs are highly abundant and mostly co-regulated in eukaryotic genomes. The structural features of bidirectional promoters (BDPs) have been well studied in yeast, humans and plants. However, the underlying mechanisms responsible for the coexpression of BDPs remain understudied, especially in plants. RESULTS: Here, we characterized chromatin features associated with rice BDPs. Several unique chromatin features were present in rice BDPs but were missing from unidirectional promoters (UDPs), including overrepresented active histone marks, canonical nucleosomes and underrepresented H3K27me3. In particular, overrepresented active marks (H3K4ac, H4K12ac, H4K16ac, H3K4me2 and H3K36me3) were truly overrepresented in type I BDPs but not in the other two BDPs, based on a Kolmogorov-Smirnov test. CONCLUSIONS: Our analyses indicate that active marks (H3K4ac, H4K12ac, H4K16ac, H3K4me3, H3K9ac and H3K27ac) may coordinate with repressive marks (H3K27me3 and H3K9me1/3) to build a unique chromatin structure that favors the coregulation of bidirectional gene pairs. Thus, our findings help to enhance the understanding of unique epigenetic mechanisms that regulate bidirectional gene pairs and may improve the manipulation of gene pairs for crop bioengineering.

The Dissection of Nitrogen Response Traits Using Drone Phenotyping and Dynamic Phenotypic Analysis to Explore N Responsiveness and Associated Genetic Loci in Wheat.

Inefficient nitrogen (N) utilization in agricultural production has led to many negative impacts such as excessive use of N fertilizers, redundant plant growth, greenhouse gases, long-lasting toxicity in ecosystem, and even effect on human health, indicating the importance to optimize N applications in cropping systems. Here, we present a multiseasonal study that focused on measuring phenotypic changes in wheat plants when they were responding to different N treatments under field conditions. Powered by drone-based aerial phenotyping and the AirMeasurer platform, we first quantified 6 N response-related traits as targets using plot-based morphological, spectral, and textural signals collected from 54 winter wheat varieties. Then, we developed dynamic phenotypic analysis using curve fitting to establish profile curves of the traits during the season, which enabled us to compute static phenotypes at key growth stages and dynamic phenotypes (i.e., phenotypic changes) during N response. After that, we combine 12 yield production and N-utilization indices manually measured to produce N efficiency comprehensive scores (NECS), based on which we classified the varieties into 4 N responsiveness (i.e., N-dependent yield increase) groups. The NECS ranking facilitated us to establish a tailored machine learning model for N responsiveness-related varietal classification just using N-response phenotypes with high accuracies. Finally, we employed the Wheat55K SNP Array to map single-nucleotide polymorphisms using N response-related static and dynamic phenotypes, helping us explore genetic components underlying N responsiveness in wheat. In summary, we believe that our work demonstrates valuable advances in N response-related plant research, which could have major implications for improving N sustainability in wheat breeding and production.

Collinearity-based marker mining for the fine mapping of Pm6, a powdery mildew resistance gene in wheat.

The genome sequences of rice (Oryza sativa L.) and Brachypodium distachyon and the comprehensive Triticeae EST (Expressed Sequence Tag) resources provide invaluable information for comparative genomics analysis. The powdery mildew resistance gene, Pm6, which was introgressed into common wheat from Triticum timopheevii, was previously mapped to the wheat chromosome bin of 2BL [fraction length (FL) 0.50-1.00] with limited DNA markers. In this study, we saturated the Pm6 locus in wheat using the collinearity-based markers by extensively exploiting these genomic resources. All wheat ESTs located in the bin 2BL FL 0.50-1.00 and their corresponding orthologous genes on rice chromosome 4 were firstly used to develop STS (Sequence Tagged Site) markers. Those identified markers that flanked the Pm6 locus were then used to identify the collinear regions in the genomes of rice and Brachypodium. Triticeae ESTs with orthologous genes in these collinear regions were further used to develop new conserved markers for the fine mapping of Pm6. Using two F(2) populations derived from crosses of IGVI-465 × Prins and IGVI-466 × Prins, we mapped a total of 29 markers to the Pm6 locus. Among them, 14 markers were co-segregated with Pm6 in the IGVI-466/Prins population. Comparative genome analysis showed that the collinear region of the 29 linked markers covers a ~5.6-Mb region in chromosome 5L of Brachypodium and a ~6.0-Mb region in chromosome 4L of rice. The marker order is conserved between rice and Brachypodium, but re-arrangements are present in wheat. Comparative mapping in the two populations showed that two conserved markers (CINAU123 and CINAU127) flanked the Pm6 locus, and an LRR-receptor-like protein kinase cluster was identified in the collinear regions of Brachypodium and rice. This putative resistance gene cluster provides a potential target site for further fine mapping and cloning of Pm6. Moreover, the newly developed conserved markers closely linked to Pm6 can be used for the marker-assisted selection (MAS) of Pm6 in wheat breeding programs.

The evolutionary history of PDR in Brachypodium distachyon polyploids.

The ATP-binding cassette transporter genes include the pleiotropic drug resistance (PDR) family found only in fungi and plants. These transporters transport toxic compounds across biological membranes. Here, we investigated the evolution of the PDR1 gene in Brachypodium distachyon, a widely distributed temperate grass species that belongs to the Poaceae (Gramineae) family, which also contains the domesticated cereal crops. Because this species has multiple ploidy levels, investigating PDR1 evolution in B. distachyon will offer insights into the formation and evolution of polyploidy. From 23 B. distachyon ecotypes, 39 PDR1 homologs were identified. All ecotypes had either one or two PDR1 copies. Based on restriction site analysis, the PDR1 homologs were classified as E or H type. All but one diploid and tetraploid ecotypes had only a single H type PDR1. All but one hexaploid ecotypes had both an E and a H type PDR1. Phylogenetic analysis revealed that each type formed a well-supported cluster. The two PDR1 types appeared to evolve differently. These different evolutionary patterns could indicate a difference in age between the two types or might indicate different mutation rates or selection pressures on the two types. The phylogenetic analysis also revealed that the hexaploid ecotypes shared a genomic origin for their E type PDR1, but there were multiple origins for hexaploid H type PDR1 homologs. Overall, the results suggest that tetraploid and hexaploid might be misnomers in B. distachyon and suggest a complex polyploidization history during B. distachyon evolution.

[Effect of rubrene position on the EL performance of the device and analysis of the exciton recombination zone].

By using an ultrathin 5, 6, 11, 12-tetraphenylnaphthacene (rubrene) layer deposited on the top of host materials, the influence of rubrene layer position on the electroluminescence (EL) spectra of organic light-emitting devices (OLEDs) was stud ied. When the rubrene layer is located at the interface between N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,18-biphenyl)-4,4'-di-amine (NPB) and tris(8-hydroxyquinoline) aluminum (AlQ) layer, EL luminescence of the device is nearly coming from rubrene emission. From the analysis of the EL spectra of the devices with different rubrene layer position, the solely contribution of rubrene and AlQ, respectively, to the luminescence of the devices is determined by spectra unmixing. Based on the analysis, the exciton length in AlQ layer is determined to be about 15-20 nm. The exciton transport and recombination characteristics are also discussed in this work.

[Molecular marker analysis of wheat-Roegneria ciliaris additions lines.].

A total of 135 EST, 27 STS, and 253 SSR primer pairs located in 7 homoeologous groups of wheat and barly were used for amplification of 24 possible Wheat-R. ciliaris disomic addition lines. Fifty-five primer pairs could amplified polymorphic bands between common wheat variety "Inayama Komugi" and the Inayama Komugi- R. ciliaris amphiploid, and 31 of the 55 could amplify the specific bands of R. ciliaris in the addition lines. According to the PCR (polymerase Chain Reaction) results, the added R. ciliaris chromosomes in lines 07K02, 07K06, 07K39, 07K201, 07K202, 07K255, and 07K256 belong to homoeologous group 1 of wheat; the added R. ciliaris chromosomes in lines 07K07, 07K08, 07K09, 07K11, 07K14, and 07K17 belong to homoeologous group 2 of wheat; the added R. ciliaris chromosomes in lines 07K15, 07K16, 07K21, and 07K47 belong to homoeologous group 6 of wheat.

[Discrimination of the Triticum aestivum-T. timopheevii introgression lines using PCR-based molecular markers].

In order to determine the fragment size of Triticum timopheevii chromosome segments introduced into wheat background and physically map the Pm6 gene, a total of 72 primers (including SSR and STS primers) were used to analyze the eight introduced introgression lines containing Pm6 gene. Referring to the available mapping information of the analyzed markers on chromosome 2B, Pm6 was physically located in distal part of the long arm of chromosome 2B at the region of Bin 2BL-6. The introgressed fragment sizes of the chromosome 2G in different introgression lines was determined to be as follow (from short to long): IGV1-465

Functional characterization of open chromatin in bidirectional promoters of rice.

Bidirectional gene pairs tend to be highly coregulated and function in similar biological processes in eukaryotic genomes. Structural features and functional consequences of bidirectional promoters (BDPs) have received considerable attention among diverse species. However, the underlying mechanisms responsible for the bidirectional transcription and coexpression of BDPs remain poorly understood in plants. In this study, we integrated DNase-seq, RNA-seq, ChIP-seq and MNase-seq data and investigated the effect of physical DNase I hypersensitive site (DHS) positions on the transcription of rice BDPs. We found that the physical position of a DHS relative to the TSS of bidirectional gene pairs can affect the expression of the corresponding genes: the closer a DHS is to the TSS, the higher is the expression level of the genes. Most importantly, we observed that the distribution of DHSs plays a significant role in the regulation of transcription and the coexpression of gene pairs, which are possibly mediated by orchestrating the positioning of histone marks and canonical nucleosomes around BDPs. Our results demonstrate that the combined actions of chromatin structures with DHSs, which contain functional cis-elements for interaction with transcriptional machinery, may play an important role in the regulation of the bidirectional transcription or coexpression in rice BDPs. Our findings may help to enhance the understanding of DHSs in the regulation of bidirectional gene pairs.

[Inheritance analysis and molecular marker selection of genes for wheat spindle streak mosaic disease resistance].

Three wheat spindle streak mosaic viruses (WSSMV) resistant cultivars ('Yining Xiaomai', 'Xu87-633', and 'Xifeng') and one susceptible cultivar ('Zhen9523') were used as parents of 3 crosses in this experiment. WSSMV resistance of the parents, F1, and F2 was evaluated under field condition. Based on the segregation ratios of resistant and susceptible plants in F, and F2 populations, it was deduced that the resistance to WSSMV was dominant and the inheritable factors controlling WSSMV resistance were encoded by the nuclear genome. WSSMV resistances in 'Yining Xiaomai' and 'Xifeng' were controlled by two pairs of alleles, which showed complementary effects. However the resistance in 'Xu-87633' was controlled by a single dominant gene. 266 pairs of SSR primers located on 21 wheat chromosomes were used for polymorphic analysis of the two resistant and the susceptible parents 'Yining Xiaomai' and 'Zhen9523', and 108 of them amplified polymorphic DNA products. By Bulk Segregant Analysis of resistant and susceptible pools, one pair of primer located on chromosome arm 2DS, Xgwm261, were found being linked to WSSMV resistance. The 224 F2 individuals were then amplified with marker Xgwm261. The statistic genetic distance between Xgwm261 and the resistance locus was calculated to be 22.9 cM using the software Mapmaker 3.0.

Competitive Expression of Endogenous Wheat CENH3 May Lead to Suppression of Alien ZmCENH3 in Transgenic Wheat × Maize Hybrids.

Uniparental chromosome elimination in wheat × maize hybrid embryos is widely used in double haploid production of wheat. Several explanations have been proposed for this phenomenon, one of which is that the lack of cross-species CENH3 incorporation may act as a barrier to interspecies hybridization. However, it is unknown if this mechanism applies universally. To study the role of CENH3 in maize chromosome elimination of wheat × maize hybrid embryos, maize ZmCENH3 and wheat αTaCENH3-B driven by the constitutive CaMV35S promoter were transformed into wheat variety Yangmai 158. Five transgenic lines for ZmCENH3 and six transgenic lines for αTaCENH3-B were identified. RT-PCR analysis showed that the transgene could be transcribed at a low level in all ZmCENH3 transgenic lines, whereas transcription of endogenous wheat CENH3 was significantly up-regulated. Interestingly, the expression levels of both wheat CENH3 and ZmCENH3 in the ZmCENH3 transgenic wheat × maize hybrid embryos were higher than those in the non-transformed Yangmai 158 × maize hybrid embryos. This indicates that the alien ZmCENH3 in wheat may induce competitive expression of endogenous wheat CENH3, leading to suppression of ZmCENH3 over-expression. Eliminations of maize chromosomes in hybrid embryos of ZmCENH3 transgenic wheat × maize and Yangmai 158 × maize were compared by observations on micronuclei presence, by marker analysis using maize SSRs (simple sequence repeats), and by FISH (fluorescence in situ hybridization) using 45S rDNA as a probe. The results indicate that maize chromosome elimination events in the two crosses are not significantly different. Fusion protein ZmCENH3-YFP could not be detected in ZmCENH3 transgenic wheat by either Western blotting or immnunostaining, whereas accumulation and loading of the αTaCENH3-B-GFP fusion protein was normal in αTaCENH3-B transgenic lines. As ZmCENH3-YFP did not accumulate after AM114 treatment, we speculate that low levels of ZmCENH3 protein in transgenic wheat may be one of the factors that lead to failure of suppression of maize chromatin elimination in ZmCENH3 transgenic wheat × maize hybrids.

NF-κB signaling inhibition and anticancer activities of LLDT-246 on human colorectal cancer HCT-116 cells in vitro.

Triptolide attracts attention for its anti-inflammatory, immune modulation, anti-proliferative and pro-apoptotic activity, but the clinical application of triptolide is restricted by its serious toxicity. Here, we demonstrate LLDT-246, a new triptolide derivative, exhibited a little more potent activity of NF-κB inhibition and cytotoxicity whether acting alone or in combination with TNF-α on colorectal cancer HCT-116 cells than its maternal compound, and showed low toxic to non-cancer cells. Mechanism study revealed that LLDT-246 inhibited phosphorylation of AKT, p-GSK3ß and p-mTOR, however, no significant effects were found on the level of p-ERK and p-JNK, along with HSP70, indicating LLDT-246 indirectly affects NF-κB and suppresses NF-κB signaling largely by interpreting AKT/GSK3ß/mTOR pathway. Altogether, LLDT-246 is a promising anticancer derivative of triptolide, further studies in vivo and about detailed mechanism of LLDT-246 is required in the future.

Development of T. aestivum L.-H. californicum alien chromosome lines and assignment of homoeologous groups of Hordeum californicum chromosomes.

Hordeum californicum (2n = 2x = 14, HH) is resistant to several wheat diseases and tolerant to lower nitrogen. In this study, a molecular karyotype of H. californicum chromosomes in the Triticum aestivum L. cv. Chinese Spring (CS)-H. californicum amphidiploid (2n = 6x = 56, AABBDDHH) was established. By genomic in situ hybridization (GISH) and multicolor fluorescent in situ hybridization (FISH) using repetitive DNA clones (pTa71, pTa794 and pSc119.2) as probes, the H. californicum chromosomes could be differentiated from each other and from the wheat chromosomes unequivocally. Based on molecular karyotype and marker analyses, 12 wheat-alien chromosome lines, including four disomic addition lines (DAH1, DAH3, DAH5 and DAH6), five telosomic addition lines (MtH7L, MtH1S, MtH1L, DtH6S and DtH6L), one multiple addition line involving H. californicum chromosome H2, one disomic substitution line (DSH4) and one translocation line (TH7S/1BL), were identified from the progenies derived from the crosses of CS-H. californicum amphidiploid with common wheat varieties. A total of 482 EST (expressed sequence tag) or SSR (simple sequence repeat) markers specific for individual H. californicum chromosomes were identified, and 47, 50, 45, 49, 21, 51 and 40 markers were assigned to chromosomes H1, H2, H3, H4, H5, H6 and H7, respectively. According to the chromosome allocation of these markers, chromosomes H2, H3, H4, H5, and H7 of H. californicum have relationship with wheat homoeologous groups 5, 2, 6, 3, and 1, and hence could be designated as 5H(c), 2H(c), 6H(c), 3H(c) and 1H(c), respectively. The chromosomes H1 and H6 were designated as 7H(c) and 4H(c), respectively, by referring to SSR markers located on rye chromosomes.

Characterization of T. aestivum-H. californicum chromosome addition lines DA2H and MA5H.

In order to transfer useful genes of Hordeum californicum into common wheat (Triticum aestivum L.), the T. aestivum c.v. Chinese Spring (CS)-H. californicum amphiploid was crossed to CS, and its backcrossing and self-fertilized progenies were analyzed by morphological observation, cytological, biochemical and molecular marker techniques. Alien addition lines with two H. californicum chromosomes were identified and their genetic constitution was characterized. STS-PCR analysis using chromosome 2B specific markers indicated that chromosome H3 of H. californicum belongs to homologous group 2, and was thus designated 2H. SDS-PAGE showed that chromosome H2 of H. californicum belongs to homologous group 5, and was designated 5H. The CS-H. californicum amphiploid and the chromosome addition lines (DA2H and MA5H) identified were evaluated for powdery mildew (Erysiphe graminis f. sp. triticii) resistance in field. The preliminary results indicated that the amphiploid showed higher powdery mildew resistance than CS. However, chromosome addition lines DA2H and MA5H were highly susceptible to powdery mildew, indicating that major powdery mildew resistant genes of H. californicum should be located on chromosomes other than 2H and 5H.

Assessment of genetic diversity of Yunnan, Tibetan, and Xinjiang wheat using SSR markers.

A total of 206 SSR (Simple Sequence Repeats) primer pairs were used to detect genetic diversity in 52 accessions of three unique wheat varieties of western China. A total of 488, 472, and 308 allelic variants were detected in 31 Yunnan, 15 Tibetan and 6 Xinjiang wheat accessions with an average of PIC values 0.2764, 0.3082, and 0.1944, respectively. Substantial differences in allelic polymorphisms were detected by SSR markers in all the 21 chromosomes, the 7 homoeologous groups, and the three genomes (A, B, and D) in Yunnan, Tibetan, and Xinjiang wheat. The highest and lowest allelic polymorphisms in all the 21 chromosomes were observed in 3B and 1D chromosomes, respectively. The lowest and highest allelic polymorphisms among the seven homoeologous groups was observed in 6 and 3 homoeologous groups, respectively. Among the three genomes, B genome showed the highest, A the intermediate, and D the lowest allelic polymorphism. The genetic distance (GD) indexes within Yunnan, Tibetan, and Xinjiang wheat, and between different wheat types were calculated. The GD value was found to be much higher within Yunnan and Tibetan wheat than within Xinjiang wheat, but the GD value between Yunnan and Tibetan wheat was lower than those between Yunnan and Xinjiang wheat, and between Tibetan and Xinjiang wheat. The cluster analysis indicated a closer relationship between Yunnan and Tibetan wheat than that between Yunnan and Xinjiang wheat or between Tibetan and Xinjiang wheat.