Mapping of sequence-specific markers and loci controlling preharvest sprouting and alpha-amylase activity in rye (Secale cereale L.) on the genetic map of an F2 (S120×S76) population

Pyramiding wheat pre-harvest sprouting resistance genes in triticale breeding

Pre -harvest sprouting (PHS) is an important problem in cereal production reducing yield and grain quality. After decades of improvement, triticale remains particularly susceptible to PHS but no resistance genes or QTLs were identified so far in this species. As wheat shares the A and B genomes with triticale, wheat PHS resistance genes can be introgressed into triticale genome by recombination after interspecific crosses. In this project, three PHS resistance genes have been transferred from wheat to triticale by marker-assisted interspecific crosses, followed by four backcrosses. The gene TaPHS1 from the 3AS chromosome of cultivar Zenkoujikomugi (Zen) and the TaMKK3 and TaQsd1, respectively located on the 4AL and 5BL chromosomes derived both from cultivar Aus1408, were pyramided in the triticale cultivar Cosinus. Only the TaPHS1 gene increases consistently the PHS resistance in triticale. The lack of efficacy of the other two genes, especially TaQsd1, could be the result of an imperfect linkage between the marker and the gene of interest. The introduction of PHS resistance genes did not alter agronomic nor disease resistance performances of triticale. This approach leads to two new, agronomically performant and PHS-resistant triticale cultivars. Today, two breeding triticale lines are ready to enter the official registration process.

How Machine Learning Methods Helped Find Putative Rye Wax Genes Among GBS Data

The standard approach to genetic mapping was supplemented by machine learning (ML) to establish the location of the rye gene associated with epicuticular wax formation (glaucous phenotype). Over 180 plants of the biparental F2 population were genotyped with the DArTseq (sequencing-based diversity array technology). A maximum likelihood (MLH) algorithm (JoinMap 5.0) and three ML algorithms: logistic regression (LR), random forest and extreme gradient boosted trees (XGBoost), were used to select markers closely linked to the gene encoding wax layer. The allele conditioning the nonglaucous appearance of plants, derived from the cultivar Karlikovaja Zelenostebelnaja, was mapped at the chromosome 2R, which is the first report on this localization. The DNA sequence of DArT-Silico 3585843, closely linked to wax segregation detected by using ML methods, was indicated as one of the candidates controlling the studied trait. The putative gene encodes the ABCG11 transporter.

The GAMYB gene in rye: sequence, polymorphisms, map location, allele-specific markers, and relationship with α-amylase activity

BACKGROUND

Transcription factor (TF) GAMYB, belonging to MYB family (named after the gene of the avian myeloblastosis virus) is a master gibberellin (GA)-induced regulatory protein that is crucial for development and germination of cereal grain and involved in anther formation. It activates many genes including high-molecular-weight glutenin and α-amylase gene families. This study presents the first attempt to characterize the rye gene encoding GAMYB in relation to its sequence, polymorphisms, and phenotypic effects.

RESULTS

ScGAMYB was mapped on rye chromosome 3R using high-density Diversity Arrays Technology (DArT)/DArTseq-based maps developed in three mapping populations. The ScGAMYB sequences were identified in RNA-seq libraries of four rye inbred lines. The transcriptome used for the search contained almost 151,000 transcripts with a median contig length of 500 nt. The average amount of total base raw data was approximately 9 GB. Comparative analysis of the ScGAMYB sequence revealed its high level of homology to wheat and barley orthologues. Single nucleotide polymorphisms (SNPs) detected among rye inbred lines allowed the development of allele specific-PCR (AS-PCR) markers for ScGAMYB that might be used to detect this gene in wide genetic stocks of rye and triticale. Segregation of the ScGAMYB alleles showed significant relationship with α-amylase activity (AMY).

CONCLUSIONS

The research showed the strong similarity of rye GAMYB sequence to its orthologues in other Graminae and confirmed the position in the genome consistent with the collinearity rule of cereal genomes. Concurrently, the ScGAMYB coding sequence (cds) showed stronger variability (24 SNPs) compared to the analogous region of wheat (5 SNPs) and barley (7 SNPs). The moderate regulatory effect of ScGAMYB on AMY was confirmed, therefore, ScGAMYB was identified as a candidate gene for partial control of α-amylase production in rye grain. The predicted structural protein change in the aa region 362-372, caused by a single SNP (C/G) at the 1100 position in ScGAMYB cds and single aa sequence change (S/C) at the 367 position, is the likely cause of the differences in the effectiveness of ScGAMYB regulatory function associated with AMY. The development of sequence-based, allele-specific (AS) PCR markers could be useful in research and application.

The application of GBS markers for extending the dense genetic map of rye (Secale cereale L.) and the localization of the Rfc1 gene restoring male fertility in plants with the C source of sterility-inducing cytoplasm

Genotyping by sequencing (GBS) is an efficient method of genotyping in numerous plant species. One of the crucial steps toward the application of GBS markers in crop improvement is anchoring them on particular chromosomes. In rye (Secale cereale L.), chromosomal localization of GBS markers has not yet been reported. In this paper, the application of GBS markers generated by the DArTseq platform for extending the high-density map of rye is presented. Additionally, their application is used for the localization of the Rfc1 gene that restores male fertility in plants with the C source of sterility-inducing cytoplasm. The total number of markers anchored on the current version of the map is 19,081, of which 18,132 were obtained from the DArTseq platform. Numerous markers co-segregated within the studied mapping population, so, finally, only 3397 unique positions were located on the map of all seven rye chromosomes. The total length of the map is 1593 cM and the average distance between markers is 0.47 cM. In spite of the resolution of the map being not very high, it should be a useful tool for further studies of the Secale cereale genome because of the presence on this map of numerous GBS markers anchored for the first time on rye chromosomes. The Rfc1 gene was located on high-density maps of the long arm of the 4R chromosome obtained for two mapping populations. Genetic maps were composed of DArT, DArTseq, and PCR-based markers. Consistent mapping results were obtained and DArTs tightly linked to the Rfc1 gene were successfully applied for the development of six new PCR-based markers useful in marker-assisted selection.

The application of high-density genetic maps of rye for the detection of QTLs controlling morphological traits

The development of genetic maps is, nowadays, one of the most intensive research activities of plant geneticists. One of the major goals of genome mapping is the localisation of quantitative trait loci (QTLs). This study was aimed at the identification of QTLs controlling morphological traits of rye and comparison of their localisation on genetic maps constructed with the use of genetically different germplasms. For QTL analyses, two high-density consensus maps of two populations (RIL-S and RIL-M) of recombinant inbred lines (RIL) were applied. Plant height (Ph), length of spikes (Sl) and the number of spikelets per spike (Sps) were studied in both populations. Additionally, the number of kernels per spike under isolation (Kps), the weight of kernels per spike (Kw) and thousand kernel weight (Tkw) were assessed in the RIL-M population. Except for Tkw, the majority of the traits were correlated to each other. The non-parametric Kruskal-Wallis (K-W) test and composite interval mapping (CIM) revealed 18/48 and 24/18 regions of rye chromosomes engaged in the determination of Ph, Sl and Sps in the RIL-S and RIL-M populations, respectively. An additional 18/15 QTLs controlling Kps, Kw and Tkw were detected on a map of the RIL-M population. A numerous group of QTLs detected via CIM remained in agreement with the genomic regions found when the K-W test was applied. Frequently, the intervals indicated by CIM were narrower.

Detection of the quantitative trait loci for α-amylase activity on a high-density genetic map of rye and comparison of their localization to loci controlling preharvest sprouting and earliness

The objectives of the research were to determine the position of quantitative trait loci (QTL) for α-amylase activity on the genetic map of a rye recombinant inbred line population-S120 × S76-and to compare them to known QTL for preharvest sprouting and heading earliness. Fourteen QTL for α-amylase activity on all seven chromosomes were identified. The detected QTL were responsible for 6.09-23.32% of α-amylase activity variation. The lowest LOD value (2.22) was achieved by locus QAa4R-M3 and the highest (7.79) by locus QAa7R-M1. Some QTL intervals for features of interest overlapped partially or completely. There were six overlapping QTL for α-amylase activity and preharvest sprouting (on 1R, 3R, 4R, 6R, 7R) and the same number for preharvest sprouting and heading earliness (on 1R, 2R, 6R, 7R). Furthermore, there was one interval partially common to all three traits, mapped on the long arm of chromosome 1R. Testing of lines originating from hybrid breeding programs, such as S120 and S76, may provide important information about the most significant genes and markers for selection in commercial breeding. Among the statistically significant markers selected in the Kruskal-Wallis test (P < 0.005), there were 55 common ones for preharvest sprouting and heading earliness (1R, 2R, 6R), 30 markers coinciding between α-amylase activity and preharvest sprouting (5R, 7R) and one marker for α-amylase activity and heading earliness (6R). ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11032-011-9627-1) contains supplementary material, which is available to authorized users.

A high density consensus map of rye (Secale cereale L.) based on DArT markers

Background

Rye (Secale cereale L.) is an economically important crop, exhibiting unique features such as outstanding resistance to biotic and abiotic stresses and high nutrient use efficiency. This species presents a challenge to geneticists and breeders due to its large genome containing a high proportion of repetitive sequences, self incompatibility, severe inbreeding depression and tissue culture recalcitrance. The genomic resources currently available for rye are underdeveloped in comparison with other crops of similar economic importance. The aim of this study was to create a highly saturated, multilocus linkage map of rye via consensus mapping, based on Diversity Arrays Technology (DArT) markers.

Methodology/Principal Findings

Recombinant inbred lines (RILs) from 5 populations (564 in total) were genotyped using DArT markers and subjected to linkage analysis using Join Map 4.0 and Multipoint Consensus 2.2 software. A consensus map was constructed using a total of 9703 segregating markers. The average chromosome map length ranged from 199.9 cM (2R) to 251.4 cM (4R) and the average map density was 1.1 cM. The integrated map comprised 4048 loci with the number of markers per chromosome ranging from 454 for 7R to 805 for 4R. In comparison with previously published studies on rye, this represents an eight-fold increase in the number of loci placed on a consensus map and a more than two-fold increase in the number of genetically mapped DArT markers.

Conclusions/Significance

Through the careful choice of marker type, mapping populations and the use of software packages implementing powerful algorithms for map order optimization, we produced a valuable resource for rye and triticale genomics and breeding, which provides an excellent starting point for more in-depth studies on rye genome organization.