Diversity and function of microbial communities in the sand sheath of Agropyron cristatum by metagenomic analysis

The roots of most gramineous plants are surrounded by a variety of microorganisms; however, few studies have focused on the rhizosheath of psammophytes. Therefore, in this study, we used Illumina HiSeq high-throughput sequencing technology to analyse the composition and functional diversity of microbial communities in the rhizosheath of sand-grown Agropyron cristatum (L.) Gaertn. We found that the number of species and functions of microbial communities gradually decreased from the rhizosheath to the bulk soil. Thus, the microbial composition of the rhizosheath was richer and more diverse, and the abundance of bacteria, including Sphingosinicella, Rhizorhabdus, Friedmanniella, Geodermatophilus, Blastococcus, and Oscillatoria, was higher, and the abundance of fungi, such as Mycothermus, was higher. The abundance of CO2 fixation-related genes (acsA, Pcc, and cbbL) in the carbon cycle; NO3–, NO2–, NH2OH, and N2 transformation genes (nrtP, nirS, hao, and nifK) in the nitrogen cycle; soxB/A/C, Sat, and dsrB genes in the sulphur cycle; and 1-phosphate mannitol dehydrogenase (MtlD) gene and polyketide synthase gene (pks) were higher in the rhizosheath than in the bulk soil, as well as genes related to phosphorus uptake in the phosphorus cycle. Our findings showed that the rhizosheath may host the predominant microbial species related to the formation of a rhizosheath.

Analysis of Chromosome Associations during Early Meiosis in Wheat Lines Carrying Chromosome Introgressions from Agropyron cristatum

Crested wheatgrass (Agropyron cristatum L. Gaertn., genome P), included in the Triticeae tribe (family Poaceae), is one of the most important grasses in temperate regions. It has been valued as a donor of important agronomic traits for wheat improvement, including tolerance to cold, drought, and high salinity, as well as resistance to leaf rust, stripe rust, and powdery mildew. For successful incorporation of beneficial alleles into wheat, it is essential that recombination between wheat and A. cristatum chromosomes occurs. In this work, we analysed chromosome associations during meiosis in wheat lines carrying chromosome introgressions from A. cristatum chromosomes 5P and 6P in the presence and absence of Ph1 locus using fluorescence in situ hybridisation. The results showed that the Ph1 locus does not affect chromosome associations between A. cristatum and wheat chromosomes because there were no interspecific chromosome associations; therefore, no recombination between chromosomes from wheat and Agropyron were observed in the absence of the Ph1 locus. The 5P and 6P A. cristatum chromosomes do not have a suppressor effect on the Ph1 locus. Wheat univalents in metaphase I suggest that Agropyron chromosomes might carry genes having a role in wheat homologous chromosome associations. Putative effect of the Agropyron genes on wheat chromosome associations does not interact with the Ph1 locus.

New Insights Into the Introgression Between Agropyron Cristatum P Genome and Wheat Genome

Agropyron cristatum (2n = 4x = 28, PPPP) is an important wild relative of common wheat and confers desirable agronomic traits to common wheat. A previous report showed that the wheat-A. cristatum 6P translocation line WAT655 carrying A. cristatum 6PS (0.81–1.00) exhibited high resistance to prevalent physiological races (CYR32 and CYR33). In this study, three disease resistance-related transcriptomes, which were mapped to A. cristatum 6PS (0.81–1.00) through the analysis of specific molecular markers, were searched from among A. cristatum full-length transcriptomes. Then, three disease resistance-related gene markers, A. cristatum P genome-specific markers, and fluorescence in situ hybridization (FISH)/genomic in situ hybridization (GISH) probes made from the DNA of three bacterial artificial chromosome (BAC) clones, three genes, and A. cristatum “Z559” were used to analyze the BC5F2 and BC5F2:3 genetic populations of the translocation line WAT655. The results revealed the introgression can spontaneously occur between A. cristatum P genome and wheat genome, and indicated the three genes could constitute a gene cluster according to the positions of their FISH signals. Additionally, kompetitive allele-specific PCR (KASP) markers of the three genes were developed to detect and acquire 24 wheat-A. cristatum breeding materials, which showed resistance to physiological races (CYR32 and CYR33) and other desirable agronomic traits according to the field investigation. In conclusion, our study not only provides new insights into the introgression between A. cristatum P genome and wheat genome, but also provides the desirable breeding materials for breeding practice.

Development and Characterization of Wheat-Agropyron cristatum Introgression Lines Induced by Gametocidal Genes and Wheat ph1b Mutant

The P genome of Agropyron cristatum Gaertn. contains many desirable genes that can be utilized as genetic resources to improve wheat. In this research, we used both the gametocidal chromosome 2Cc and the pairing homologous gene (Ph1b) mutant to induce structural aberrations and translocations between wheat and the 4P, 5P, and 6P genome chromosomes. By using the two approaches, a total of 19 wheat-A. cristatum translocations have been identified, in which 13 were induced by the Triticum aestivum cv. Chinese Spring (CS) ph1b mutant (CS ph1b) and six were induced by gametocidal chromosome 2Cc from Aegilops cylindrica Host. The wheat-4P, -5P and -6P A. cristatum translocations were characterized by in situ hybridization and by a set of conserved orthologous set (COS) molecular markers. The aberrations included centromeric translocations, terminal translocations, dicentric translocations, and deletions. The average induction frequency of chromosome structural aberrations was 10.9% using gametocidal 2Cc chromosome and 8.8% using ph1b mutant. The highest frequency obtained was for chromosome 4P using both approaches. All the wheat-A. cristatum translocation lines obtained were valuable for identifying A. cristatum chromosome 4P, 5P, and 6P related genes. In addition, these lines provided genetic resources and new germplasm accessions for the genetic improvement of wheat.