Addition of Aegilops biuncialis chromosomes 2M or 3M improves the salt tolerance of wheat in different way

Coping with salinity stress: segmental group 7 chromosome introgressions from halophytic Thinopyrum species greatly enhance tolerance of recipient durum wheat

Increased soil salinization, tightly related to global warming and drought and exacerbated by intensified irrigation supply, implies highly detrimental effects on staple food crops such as wheat. The situation is particularly alarming for durum wheat (DW), better adapted to arid/semi-arid environments yet more sensitive to salt stress than bread wheat (BW). To enhance DW salinity tolerance, we resorted to chromosomally engineered materials with introgressions from allied halophytic Thinopyrum species. "Primary" recombinant lines (RLs), having portions of their 7AL arms distally replaced by 7el1L Th. ponticum segments, and "secondary" RLs, harboring Th. elongatum 7EL insertions "nested" into 7el1L segments, in addition to near-isogenic lines lacking any alien segment (CLs), cv. Om Rabia (OR) as salt tolerant control, and BW introgression lines with either most of 7el1 or the complete 7E chromosome substitution as additional CLs, were subjected to moderate (100 mM) and intense (200 mM) salt (NaCl) stress at early growth stages. The applied stress altered cell cycle progression, determining a general increase of cells in G1 and a reduction in S phase. Assessment of morpho-physiological and biochemical traits overall showed that the presence of Thinopyrum spp. segments was associated with considerably increased salinity tolerance versus its absence. For relative water content, Na+ accumulation and K+ retention in roots and leaves, oxidative stress indicators (malondialdehyde and hydrogen peroxide) and antioxidant enzyme activities, the observed differences between stressed and unstressed RLs versus CLs was of similar magnitude in "primary" and "secondary" types, suggesting that tolerance factors might reside in defined 7el1L shared portion(s). Nonetheless, the incremental contribution of 7EL segments emerged in various instances, greatly mitigating the effects of salt stress on root and leaf growth and on the quantity of photosynthetic pigments, boosting accumulation of compatible solutes and minimizing the decrease of a powerful antioxidant like ascorbate. The seemingly synergistic effect of 7el1L + 7EL segments/genes made "secondary" RLs able to often exceed cv. OR and equal or better perform than BW lines. Thus, transfer of a suite of genes from halophytic germplasm by use of fine chromosome engineering strategies may well be the way forward to enhance salinity tolerance of glycophytes, even the sensitive DW.

Chromosome genomics facilitates the marker development and selection of wheat-Aegilops biuncialis addition, substitution and translocation lines

The annual goatgrass, Aegilops biuncialis is a rich source of genes with considerable agronomic value. This genetic potential can be exploited for wheat improvement through interspecific hybridization to increase stress resistance, grain quality and adaptability. However, the low throughput of cytogenetic selection hampers the development of alien introgressions. Using the sequence of flow-sorted chromosomes of diploid progenitors, the present study enabled the development of chromosome-specific markers. In total, 482 PCR markers were validated on wheat (Mv9kr1) and Ae. biuncialis (MvGB642) crossing partners, and 126 on wheat-Aegilops additions. Thirty-two markers specific for U- or M-chromosomes were used in combination with GISH and FISH for the screening of 44 Mv9kr1 × Ae. biuncialis BC3F3 genotypes. The predominance of chromosomes 4M and 5M, as well as the presence of chromosomal aberrations, may indicate that these chromosomes have a gametocidal effect. A new wheat-Ae. biuncialis disomic 4U addition, 4M(4D) and 5M(5D) substitutions, as well as several introgression lines were selected. Spike morphology and fertility indicated that the Aegilops 4M or 5M compensated well for the loss of 4D and 5D, respectively. The new cytogenetic stocks represent valuable genetic resources for the introgression of key genes alleles into wheat.

Flow karyotyping of wheat-Aegilops additions facilitate dissecting the genomes of Ae. biuncialis and Ae. geniculata into individual chromosomes

Breeding of wheat adapted to new climatic conditions and resistant to diseases and pests is hindered by a limited gene pool due to domestication and thousands of years of human selection. Annual goatgrasses (Aegilops spp.) with M and U genomes are potential sources of the missing genes and alleles. Development of alien introgression lines of wheat may be facilitated by the knowledge of DNA sequences of Aegilops chromosomes. As the Aegilops genomes are complex, sequencing relevant Aegilops chromosomes purified by flow cytometric sorting offers an attractive route forward. The present study extends the potential of chromosome genomics to allotetraploid Ae. biuncialis and Ae. geniculata by dissecting their M and U genomes into individual chromosomes. Hybridization of FITC-conjugated GAA oligonucleotide probe to chromosomes suspensions of the two species allowed the application of bivariate flow karyotyping and sorting some individual chromosomes. Bivariate flow karyotype FITC vs. DAPI of Ae. biuncialis consisted of nine chromosome-populations, but their chromosome content determined by microscopic analysis of flow sorted chromosomes indicated that only 7M^b and 1U^b could be sorted at high purity. In the case of Ae. geniculata, fourteen chromosome-populations were discriminated, allowing the separation of nine individual chromosomes (1M^g, 3M^g, 5M^g, 6M^g, 7M^g, 1U^g, 3U^g, 6U^g, and 7U^g) out of the 14. To sort the remaining chromosomes, a partial set of wheat-Ae. biuncialis and a whole set of wheat-Ae. geniculata chromosome addition lines were also flow karyotyped, revealing clear separation of the GAA-rich Aegilops chromosomes from the GAA-poor A- and D-genome chromosomes of wheat. All of the alien chromosomes represented by individual addition lines could be isolated at purities ranging from 74.5% to 96.6% and from 87.8% to 97.7%, respectively. Differences in flow karyotypes between Ae. biuncialis and Ae. geniculata were analyzed and discussed. Chromosome-specific genomic resources will facilitate gene cloning and the development of molecular tools to support alien introgression breeding of wheat.

Mapping of the novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis based on ph1b-induced homoeologous recombination

A novel powdery mildew resistance gene Pm2Mb from Aegilops biuncialis was transferred into common wheat and mapped to chromosome 2M^bL bin FL 0.49-0.66 by molecular cytogenetic analysis of 2M^b recombinants. Aegilops biuncialis, a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies identified that chromosome 2M^b in Chinese Spring (CS)-Ae. biuncialis 2M^b disomic addition line TA7733 conferred high resistance to powdery mildew, and the resistance gene was temporarily designated as Pm2Mb. In this study, a total of 65 CS-Ae. biuncialis 2M^b recombinants were developed by ph1b-induced homoeologous recombination and they were grouped into 12 different types based on the presence of different markers of 2M^b-specificity. Segment sizes and breakpoints of each 2M^b recombinant type were further characterized using in situ hybridization and molecular marker analyses. Powdery mildew responses of each type were assessed by inoculation of each 2M^b recombinant-derived F₂ progenies using the isolate E05. Combined analyses of in situ hybridization, molecular markers and powdery mildew resistance data of the 2M^b recombinants, the gene Pm2Mb was cytologically located to an interval of FL 0.49-0.66 in the long arm of 2M^b, where 19 2M^b-specific markers were located. Among the 65 2M^b recombinants, T-11 (T2DS.2DL-2M^bL) and T-12 (Ti2DS.2DL-2M^bL-2DL) contained a small 2M^bL segment harboring Pm2Mb. Besides, a physical map of chromosome 2M^b was constructed with 70 2M^b-specific markers in 10 chromosomal bins and the map showed that submetacentric chromosome 2M^b of Ae. biuncialis was rearranged by a terminal intrachromosomal translocation. The newly developed 2M^b recombinants with powdery mildew resistance, the 2M^b-specific molecular markers and the physical map of chromosome 2M^b will benefit wheat disease breeding as well as fine mapping and cloning of Pm2Mb.

Transfer of the ph1b Deletion Chromosome 5B From Chinese Spring Wheat Into a Winter Wheat Line and Induction of Chromosome Rearrangements in Wheat-Aegilops biuncialis Hybrids

Effective utilization of genetic diversity in wild relatives to improve wheat requires recombination between wheat and alien chromosomes. However, this is suppressed by the Pairing homoeologous gene, Ph1, on the long arm of wheat chromosome 5B. A deletion mutant of the Ph1 locus (ph1b) has been used widely to induce homoeologous recombination in wheat × alien hybrids. However, the original ph1b mutation, developed in Chinese Spring (CS) background has poor agronomic performance. Hence, alien introgression lines are first backcrossed with adapted wheat genotypes and after this step, alien chromosome segments are introduced into breeding lines. In this work, the ph1b mutation was transferred from two CSph1b mutants into winter wheat line Mv9kr1. Homozygous genotypes Mv9kr1 ph1b/ph1b exhibited improved plant and spike morphology compared to Chinese Spring. Flow cytometric chromosome analysis confirmed reduced DNA content of the mutant 5B chromosome in both wheat genotype relative to the wild type chromosome. The ph1b mutation in the Mv9kr1 genotype allowed wheat-alien chromosome pairing in meiosis of Mv9kr1ph1b_K × Aegilops biuncialis F₁ hybrids, predominantly with the M^b-genome chromosomes of Aegilops relative to those of the U^b genome. High frequency of wheat-Aegilops chromosome interactions resulted in rearranged chromosomes identified in the new Mv9kr1ph1b × Ae. Biuncialis amphiploids, making these lines valuable sources for alien introgressions. The new Mv9kr1ph1b mutant genotype is a unique resource to support alien introgression breeding of hexaploid wheat.

Towards rainbow portable Cytophone with laser diodes for global disease diagnostics

In vivo, Cytophone has demonstrated the capability for the early diagnosis of cancer, infection, and cardiovascular disorders through photoacoustic detection of circulating disease markers directly in the bloodstream with an unprecedented 1,000-fold improvement in sensitivity. Nevertheless, a Cytophone with higher specificity and portability is urgently needed. Here, we introduce a novel Cytophone platform that integrates a miniature multispectral laser diode array, time-color coding, and high-speed time-resolved signal processing. Using two-color (808 nm/915 nm) laser diodes, we demonstrated spectral identification of white and red clots, melanoma cells, and hemozoin in malaria-infected erythrocytes against a blood background and artifacts. Data from a Plasmodium yoelii murine model and cultured human P. falciparum were verified in vitro with confocal photothermal and fluorescent microscopy. With these techniques, we detected infected cells within 4 h after invasion, which makes hemozoin promising as a spectrally selective marker at the earliest stages of malaria progression. Along with the findings from our previous application of Cytophone with conventional lasers for the diagnosis of melanoma, bacteremia, sickle anemia, thrombosis, stroke, and abnormal hemoglobin forms, this current finding suggests the potential for the development of a portable rainbow Cytophone with multispectral laser diodes for the identification of these and other diseases.

Identification of New QTLs for Dietary Fiber Content in Aegilops biuncialis

Grain dietary fiber content is an important health-promoting trait of bread wheat. A dominant dietary fiber component of wheat is the cell wall polysaccharide arabinoxylan and the goatgrass Aegilops biuncialis has high β-glucan content, which makes it an attractive gene source to develop wheat lines with modified fiber composition. In order to support introgression breeding, this work examined genetic variability in grain β-glucan, pentosan, and protein content in a collection of Ae. biuncialis. A large variation in grain protein and edible fiber content was revealed, reflecting the origin of Ae. biuncialis accessions from different eco-geographical habitats. Association analysis using DArTseq-derived SNPs identified 34 QTLs associated with β-glucan, pentosan, water-extractable pentosan, and protein content. Mapping the markers to draft chromosome assemblies of diploid progenitors of Ae. biuncialis underlined the role of genes on chromosomes 1M^b, 4M^b, and 5M^b in the formation of grain β-glucan content, while other QTLs on chromosome groups 3, 6, and 1 identified genes responsible for total- and water-extractable pentosan content. Functional annotation of the associated marker sequences identified fourteen genes, nine of which were identified in other monocots. The QTLs and genes identified in the present work are attractive targets for chromosome-mediated gene transfer to improve the health-promoting properties of wheat-derived foods.

Draft Sequencing Crested Wheatgrass Chromosomes Identified Evolutionary Structural Changes and Genes and Facilitated the Development of SSR Markers

Crested wheatgrass (Agropyron cristatum), a wild relative of wheat, is an attractive source of genes and alleles for their improvement. Its wider use is hampered by limited knowledge of its complex genome. In this work, individual chromosomes were purified by flow sorting, and DNA shotgun sequencing was performed. The annotation of chromosome-specific sequences characterized the DNA-repeat content and led to the identification of genic sequences. Among them, genic sequences homologous to genes conferring plant disease resistance and involved in plant tolerance to biotic and abiotic stress were identified. Genes belonging to the important groups for breeders involved in different functional categories were found. The analysis of the DNA-repeat content identified a new LTR element, Agrocen, which is enriched in centromeric regions. The colocalization of the element with the centromeric histone H3 variant CENH3 suggested its functional role in the grass centromere. Finally, 159 polymorphic simple-sequence-repeat (SSR) markers were identified, with 72 of them being chromosome- or chromosome-arm-specific, 16 mapping to more than one chromosome, and 71 mapping to all the Agropyron chromosomes. The markers were used to characterize orthologous relationships between A. cristatum and common wheat that will facilitate the introgression breeding of wheat using A. cristatum.