Genome-wide profiling of genetic variations reveals the molecular basis of aluminum stress adaptation in Tibetan wild barley

Aluminum (Al) toxicity in acidic soil is a major factor affecting crop productivity. The extensive genetic diversity found in Tibetan wild barley germplasms offers a valuable reservoir of alleles associated with aluminum tolerance. Here, resequencing of two Al-tolerant barley genotypes (Tibetan wild barley accession XZ16 and cultivated barley Dayton) identified a total of 19,826,182 and 16,287,277 single nucleotide polymorphisms (SNPs), 1628,052 and 1386,973 insertions/deletions (InDels), 61,532 and 57,937 structural variations (SVs), 248,768 and 240,723 copy number variations (CNVs) in XZ16 and Dayton, respectively, and uncovered approximately 600 genes highly related to Al tolerance in barley. Comparative genomic analyses unveiled 71 key genes that contain unique genetic variants in XZ16 and are predominantly associated with organic acid exudation, Al sequestration, auxin response, and transcriptional regulation. Manipulation of these key genes at the genetic and transcriptional level is a promising strategy for developing optimal haplotype combinations and new barley cultivars with improved Al tolerance. This study represents the first comprehensive examination of genetic variation in Al-tolerant Tibetan wild barley through genome-wide profiling. The obtained results make the deep insight into the mechanisms underlying barley adaptation to Al toxicity, and identified the candidate genes useful for improvement of Al tolerance in barley.

Identification of QTLs conferring resistance to scald (Rhynchosporium commune) in the barley nested association mapping population HEB-25

BACKGROUND

Barley scald, caused by the fungus Rhynchosporium commune, is distributed worldwide to all barley growing areas especially in cool and humid climates. Scald is an economically important leaf disease resulting in yield losses of up to 40%. To breed resistant cultivars the identification of quantitative trait loci (QTLs) conferring resistance to scald is necessary. Introgressing promising resistance alleles of wild barley is a way to broaden the genetic basis of scald resistance in cultivated barley. Here, we apply nested association mapping (NAM) to map resistance QTLs in the barley NAM population HEB-25, comprising 1420 lines in BC1S3 generation, derived from crosses of 25 wild barley accessions with cv. Barke.

RESULTS

In scald infection trials in the greenhouse variability of resistance across and within HEB-25 families was found. NAM based on 33,005 informative SNPs resulted in the identification of eight reliable QTLs for resistance against scald with most wild alleles increasing resistance as compared to cv. Barke. Three of them are located in the region of known resistance genes and two in the regions of QTLs, respectively. The most promising wild allele was found at Rrs17 in one specific wild donor. Also, novel QTLs with beneficial wild allele effects on scald resistance were detected.

CONCLUSIONS

To sum up, wild barley represents a rich resource for scald resistance. As the QTLs were linked to the physical map the identified candidate genes will facilitate cloning of the scald resistance genes. The closely linked flanking molecular markers can be used for marker-assisted selection of the respective resistance genes to integrate them in elite cultivars.

Characterization of the Barley Net Blotch Pathosystem at the Center of Origin of Host and Pathogen

Net blotch (NB) is a major disease of barley caused by the fungus Pyrenophora teres f. teres (Ptt), and P. teres f. maculata (Ptm). Ptt and Ptm infect the cultivated crop (Hordeum vulgare) and its wild relatives (H. vulgare ssp. spontaneum and H. murinum ssp. glaucum). The main goal of this research was to study the NB-causing pathogen in the crop center of origin. To address this, we have constructed a Ptt (n = 15) and Ptm (n = 12) collection isolated from three barley species across Israel. Isolates were characterized genetically and phenotypically. Aggressiveness of the isolates was determined based on necrotrophic growth rate on detached leaves of barley. In addition, isolates were genetically characterized by the mating type, followed by phylogenetic analysis, clustering them into seven groups. The analysis showed no significant differentiation of isolates based on either geographic origin, host of origin or form (Ptt vs. Ptm). Nevertheless, there was a significant difference in aggressiveness among the isolates regardless of host species, geographic location or sampling site. Moreover, it was apparent that the isolates derived from wild hosts were more variable in their necrotrophic growth rate, compared to isolates sampled from cultivated hosts, thereby suggesting that NB plays a major role in epidemiology at the center of barley origin where most of the diversity lies. Ptm has significantly higher necrotrophic and saprotrophic growth rates than Ptt, and for both a significant negative correlation was found between light intensity exposure and growth rates.

spontaneum for the Development of a Transposon-Based Insertional Mutagenesis System

Domestication and intensive selective breeding of plants has triggered erosion of genetic diversity of important stress-related alleles. Researchers highlight the potential of using wild accessions as a gene source for improvement of cereals such as barley, which has major economic and social importance worldwide. Previously, we have successfully introduced the maize Ac/Ds transposon system for gene identification in cultivated barley. The objective of current research was to investigate the response of Hordeum vulgare ssp. spontaneum wild barley accessions in tissue culture to standardize parameters for introduction of Ac/Ds transposons through genetic transformation. We investigated the response of ten wild barley genotypes for callus induction, regenerative green callus induction and regeneration of fertile plants. The activity of exogenous Ac/Ds elements was observed through a transient assay on immature wild barley embryos/callus whereby transformed embryos/calli were identified by the expression of GUS. Transient Ds expression bombardment experiments were performed on 352 pieces of callus (3-5 mm each) or immature embryos in 4 genotypes of wild barley. The transformation frequency of putative transgenic callus lines based on transient GUS expression ranged between 72 and100 % in wild barley genotypes. This is the first report of a transformation system in H. vulgare ssp. spontaneum.