Genetic mapping of pre-harvest sprouting resistance loci in bread wheat (Triticum aestivum L.)

Non-Peer ReviewedPre-harvest sprouting (PHS) in bread wheat (Triticum aestivum L.) is the germination of mature grain while still in spike. PHS causes downgrading of grain quality which severely limits its end use. In western Canada, cool and wet weather during harvest makes the crops susceptible to PHS. Breeding for PHS tolerance in wheat is challenging on phenotypic basis because PHS is inherited quantitatively and strongly affected by environmental conditions. A mapping population of one hundred and fifty one doubled haploid (DH) lines from a cross between two spring wheat cultivars ND690 (non-dormant) and W98616 (dormant) was developed for genetic mapping of PHS resistance loci. Initially, 20 dormant and 20 non dormant lines were used for genetic mapping with SSR (Simple sequence repeat) and AFLP (Amplified Fragment Length Polymorphism) markers. A total of 550 markers (300 SSR markers and 250 AFLP) markers have been mapped on different chromosomes. Five chromosomal regions on the chromosomes 1A, 3B, 4A, 5B and 6B associated with pre-harvest sprouting were identified in this study

Allelic diversity of HMW and LMW glutenin subunits and ω-gliadins in Canadian hard red spring bread wheat (Triticum aestivum L.) developed over 150 years

Non-Peer ReviewedWheat (Triticum aestivum L.) is a major cereal crop that is grown around the world. Wheat based products are an important component of human diet as source of calories and proteins. The wheat grain storage proteins are made up of glutenin and gliadin subunits that form gluten in the dough, when wheat flour is mixed with water. The viscoelastic properties of wheat dough lend itself to make diverse food products consumed around the world. During the past few years, wheat gluten has been blamed for increased incidence of some chronic diseases such as obesity and associated cardiovascular ailments and type-2 diabetes. The main objective of this study was to study the diversity in wheat glutenins and gliadins, the two proteins that make up gluten, during 150 years of wheat improvement in Canada. A set of 37 hard red spring wheat cultivars were grown during 2013 and 2014, in a randomized complete block design with four replicates at the Kernen farm, University of Saskatchewan. Cultivars were selected based on the year of release from 1860 to 2007 and subdivided into historical and modern wheats. Historical cultivars included 11 entries released in Canada from 1860 until 1935 and the modern group included 26 cultivars released after 1935 and up to 2007. Gluten protein composition was determined by SDS-PAGE. Most of the genotypes in both groups had the combination Glu-A1b (2*), Glu-B1c (7+9) and Glu-D1d (5+10) for the high molecular weight glutenins (HMW-GS). Another allele that remained stable was the low molecular weight glutenin (LMW-GS) Glu-A3e present in 91% (historical) to 58% (modern) of the cultivars. Most variation was observed in the frequency of appearance of the most common subunits in the LMW-GS Glu-B3 and Glu-D3. For instance, in the historical group, the most common alleles were the Glu-B3b’ (55%) and the Glu-D3a (37%) or Glu-D3b (36%) whereas in modern cultivars Glu-B3h (58%) and the Glu-D3c (58%) were most frequent. Regarding ω-gliadins encoded by the Gli-B1, a relative high proportion of the historical genotypes carried the Gli-B1b subunit whereas in modern cultivars the Gli-B1d (58%) was common. No major alterations in the gluten subunits were observed between the Canadian historical and modern hard red spring wheat cultivars developed over the last century and half. However, subtle differences were found in the HMW-GS and the LMW-GS Glu-A3, and the frequency of appearance in the Glu-D3 and Glu-B3 (LMW-GS) and the Gli-B1 (ω-gliadins). The impact of the alterations on the incidence of Celiac disease is currently being studied

Identification and validation of QTLs associated with pre-harvest sprouting tolerance in bread wheat

Non-Peer ReviewedPre-harvest sprouting (PHS) is the in-spike germination of physiologically mature grain in response to relatively high humidity due to untimely rains prior to harvest. PHS in bread wheat (Triticum aestivum L.) results in substantial economic loss, as it decreases the functional quality of wheat grain. The Canadian Grain Commission sets the limit of percentage severely sprouted and total sprouted grain depending on the grade and wheat classes. Pre-harvest sprouted wheat is reduced in grade and value, depending on the quantity of sprouted kernels present in a sample. Breeding for PHS tolerance in wheat is challenging on phenotypic basis because PHS is inherited quantitatively and highly influenced by environmental conditions. Seed dormancy is the main factor responsible for conferring the PHS resistance to the grains of bread wheat. The objectives of this study were to identify and validate the major quantitative loci (QTL) for pre-harvest sprouting (PHS) resistance in bread wheat. A F1-derived doubled haploid (DH) population of 151 lines from a cross between two spring wheat cultivars ND690 (nondormant) and W98616 (dormant) was used to identify the genomic regions associated with PHS tolerance. A total of 950 polymorphic markers (369 SSR, 306 AFLP, 267 DArT and 8 EST) have been used to develop a genetic map and to identify QTLs for PHS tolerance. Interval mapping revealed a major QTL on chromosome 4A explaining 25% phenotypic variation in this mapping population. Forty two Canadian wheat cultivars and germplasm lines were screened with the DNA marker in the QTL region on chromosome 4A for validation. 113 BC1F1 plants from four different backcrosses were screened with the marker associated with PHS resistance. Marker assisted back crossing reduced the population size in BC1F1 generation by 40.7%. This information will help the plant breeders to pyramid this QTL with other QTLs from different PHS resistance sources

Comparative expression of Cbf genes in the Triticeae under different acclimation induction temperatures

In plants, the C-repeat binding factors (Cbfs) are believed to regulate low-temperature (LT) tolerance. However, most functional studies of Cbfs have focused on characterizing expression after an LT shock and have not quantified differences associated with variable temperature induction or the rate of response to LT treatment. In the Triticeae, rye (Secale cereale L.) is one of the most LT-tolerant species, and is an excellent model to study and compare Cbf LT induction and expression profiles. Here, we report the isolation of rye Cbf genes (ScCbfs) and compare their expression levels in spring- and winter-habit rye cultivars and their orthologs in two winter-habit wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) cultivars. Eleven ScCbfs were isolated spanning all four major phylogenetic groups. Nine of the ScCbfs mapped to 5RL and one to chromosome 2R. Cbf expression levels were variable, with stronger expression in winter- versus spring-habit rye cultivars but no clear relationship with cultivar differences in LT, down-stream cold-regulated gene expression and Cbf expression were detected. Some Cbfs were expressed only at warmer acclimation temperatures in all three species and their expression was repressed at the end of an 8-h dark period at warmer temperatures, which may reflect a temperature-dependent, light-regulated diurnal response. Our work indicates that Cbf expression is regulated by complex genotype by time by induction–temperature interactions, emphasizing that sample timing, induction–temperature and light-related factors must receive greater consideration in future studies involving functional characterization of LT-induced genes in cereals

The CBF gene family in hexaploid wheat and its relationship to the phylogenetic complexity of cereal CBFs

Most temperate plants tolerate both chilling and freezing temperatures whereas many species from tropical regions suffer chilling injury when exposed to temperatures slightly above freezing. Cold acclimation induces the expression of cold-regulated genes needed to protect plants against freezing stress. This induction is mediated, in part, by the CBF transcription factor family. To understand the evolution and function of this family in cereals, we identified and characterized 15 different CBF genes from hexaploid wheat. Our analyses reveal that wheat species, T. aestivum and T. monococcum, may contain up to 25 different CBF genes, and that Poaceae CBFs can be classified into 10 groups that share a common phylogenetic origin and similar structural characteristics. Six of these groups (IIIc, IIId, IVa, IVb, IVc and IVd) are found only in the Pooideae suggesting they represent the CBF response machinery that evolved recently during colonization of temperate habitats. Expression studies reveal that five of the Pooideae-specific groups display higher constitutive and low temperature inducible expression in the winter cultivar, and a diurnal regulation pattern during growth at warm temperature. The higher constitutive and inducible expression within these CBF groups is an inherited trait that may play a predominant role in the superior low temperature tolerance capacity of winter cultivars and possibly be a basis of genetic variability in freezing tolerance within the Pooideae subfamily

Genetic variants of HvCbf14 are statistically associated with frost tolerance in a European germplasm collection of Hordeum vulgare

Two quantitative trait loci (Fr-H1 and Fr-H2) for frost tolerance (FT) have been discovered on the long arm of chromosome 5H in barley. Two tightly linked groups of CBF genes, known to play a key role in the FT regulatory network in A. thaliana, have been found to co-segregate with Fr-H2. Here, we investigate the allelic variations of four barley CBF genes (HvCbf3, HvCbf6, HvCbf9 and HvCbf14) in a panel of European cultivars, landraces and H. spontaneum accessions. In the cultivars a reduction of nucleotide and haplotype diversities in CBFs compared with the landraces and the wild ancestor H. spontaneum, was evident. In particular, in cultivars the loss of HvCbf9 genetic variants was higher compared to other sequences. In order to verify if the pattern of CBF genetic variants correlated with the level of FT, an association procedure was adopted. The pairwise analysis of linkage disequilibrium (LD) among the genetic variants in four CBF genes was computed to evaluate the resolution of the association procedure. The pairwise plotting revealed a low level of LD in cultivated varieties, despite the tight physical linkage of CBF genes analysed. A structured association procedure based on a general liner model was implemented, including the variants in CBFs, of Vrn-H1, and of two reference genes not involved in FT (α-Amy1 and Gapdh) and considering the phenotypic data for FT. Association analysis recovered two nucleotide variants of HvCbf14 and one nucleotide variant of Vrn-H1 as statistically associated to FT

Hv-CBF2A overexpression in barley accelerates COR gene transcript accumulation and acquisition of freezing tolerance during cold acclimation

Abstract C-Repeat Binding Factors (CBFs) are DNAbinding transcriptional activators of gene pathways imparting freezing tolerance. Poaceae contain three CBF subfamilies, two of which, HvCBF3/CBFIII and HvCBF4/CBFIV, are unique to this taxon. To gain mechanistic insight into HvCBF4/CBFIV CBFs we overexpressed Hv-CBF2A in spring barley (Hordeum vulgare) cultivar ‘Golden Promise’. The Hv-CBF2A overexpressing lines exhibited stunted growth, poor yield, and greater freezing tolerance compared to non-transformed ‘Golden Promise’. Differences in freezing tolerance were apparent only upon cold acclimation. During cold acclimation freezing tolerance of the Hv-CBF2A overexpressing lines increased more rapidly than that of ‘Golden Promise’ and paralleled the freezing tolerance of the winter hardy barley ‘Dicktoo’. Transcript levels of candidate CBF target genes, COR14B and DHN5 were increased in the overexpressor lines at warm temperatures, and at cold temperatures they accumulated to much higher levels in the Hv-CBF2A overexpressors than in ‘Golden Promise’. Hv-CBF2A overexpression also increased transcript levels of other CBF genes at FROST RESISTANCE-H2-H2 (FR-H2) possessing CRT/DRE sites in their upstream regions, the most notable of which was CBF12. CBF12 transcript levels exhibited a relatively constant incremental increase above levels in ‘Golden Promise’ both at warm and cold. These data indicate that Hv-CBF2A activates target genes at warm temperatures and that transcript accumulation for some of these targets is greatly enhanced by cold temperatures