Zhenying Dong

Dissecting and Enhancing the Contributions of High-Molecular-Weight Glutenin Subunits to Dough Functionality and Bread Quality

Dear Editor, Seed storage proteins (SSPs) are frequently important determinants of crop quality traits (Shewry and Casey,1999).Dissecting and enhancing the genetic contributions of individual SSPs to their target traits are essential for effectively improving crop quality attributes.However,such a task is often difficult to accomplish,because SSPs are frequently expressed from multigene families and exhibit strong allelic variation.Consequently,detailed knowledge of the function of individual SSPs in crop quality trait is still limited.This scenario is well illustrated by high-molecular-weight glutenin subunits (HMWGSs),a complex family of SSPs that are involved in wheat enduse quality through affecting dough functionality (Bekes,2012;Rasheed et al.,2014).

Haplotype Variation of Glu-D1 Locus and the Origin of Glu-D1d Allele Conferring Superior End-Use Qualities in Common Wheat

In higher plants, seed storage proteins (SSPs) are frequently expressed from complex gene families, and allelic variation of SSP genes often affects the quality traits of crops. In common wheat, the Glu-D1 locus, encoding 1Dx and 1Dy SSPs, has multiple alleles. The Glu-D1d allele frequently confers superior end-use qualities to commercial wheat varieties. Here, we studied the haplotype structure of Glu-D1 genomic region and the origin of Glu-D1d. Using seven diagnostic DNA markers, 12 Glu-D1 haplotypes were detected among common wheat, European spelt wheat (T. spelta, a primitive hexaploid relative of common wheat), and Aegilops tauschii (the D genome donor of hexaploid wheat). By comparatively analyzing Glu-D1 haplotypes and their associated 1Dx and 1Dy genes, we deduce that the haplotype carrying Glu-D1d was likely differentiated in the ancestral hexaploid wheat around 10,000 years ago, and was subsequently transmitted to domesticated common wheat and T. spelta. A group of relatively ancient Glu-D1 haplotypes was discovered in Ae. tauschii, which may serve for the evolution of other haplotypes. Moreover, a number of new Glu-D1d variants were found in T. spelta. The main steps in Glu-D1d differentiation are proposed. The implications of our work for enhancing the utility of Glu-D1d in wheat quality improvement and studying the SSP alleles in other crop species are discussed.

Nanochannel system fabricated by MEMS microfabrication and atomic force microscopy

A silicon nanochannel system with integrated transverse electrodes was designed and fabricated by combining micro-electro-mechanical systems (MEMS) micromachining and atomic force microscopy (AFM)-based nanolithography. The fabrication process began with the patterning of microscale reservoirs and electrodes on an oxidised silicon chip using conventional MEMS techniques. A nanochannel, approximately 30 [micro sign]m long with a small semi-circular cross-sectional area of 20 nm × 200 nm, was then mechanically machined on the oxide surface between the micro reservoirs by applying AFM nanolithography with an all-diamond probe. Anodic bonding was used to seal off the nanochannel with a matching Pyrex cover. Continuous flow in the nanochannel was verified by pressurising a solution of fluorescein isothiocyanate in ethanol through the nanochannel in a vacuum chamber. It was further demonstrated by translocating negatively charged nanobeads (diameter approximately 20 nm) through the nanochannel by using an external DC electric field. The passage of the nanobeads caused a sharp increase in the transverse electrical conductivity of the nanochannel.

High-throughput mining of E-genome-specific SNPs for characterizing Thinopyrum elongatum introgressions in common wheat

Diploid Thinopyrum elongatum (EE, 2n = 2x = 14) and related polyploid species constitute an important gene pool for improving Triticeae grain and forage crops. However, the genomic and molecular marker resources are generally poor for these species. To aid the genetic, molecular, breeding and ecological studies involving Thinopyrum species, we developed a strategy for mining and validating E‐genome‐specific SNPs using Th. elongatum and common wheat (Triticum aestivum, AABBDD, 2n = 6x = 42) as experimental materials. By comparing the transcriptomes between Chinese Spring (CS, a common wheat variety) and the CS‐Th. elongatum octoploid, 35,193 candidate SNPs between E genome genes and their common wheat orthologs were computed. Through comparative genomic analysis, these SNPs were putatively assigned to the seven individual E genome chromosomes. Among 420 randomly selected SNPs, 373 could be validated. Thus, approximately 89% of the mined SNPs may be authentic with respect to their polymorphism and chromosomal location. Using 14 such SNPs as molecular markers, complex E genome introgressions were reliably identified in 78 common wheat‐Th. elongatum hybrids, and the structural feature of a novel recombinant chromosome formed by 6E and 7E was revealed. Finally, based on testing 33 SNPs assigned to chromosome 3E in multiple genotypes of Th. elongatum, Pseudoroegneria stipifolia (carrying the St genome related to E) and common wheat, we suggest that some of the SNP markers may also be applicable for genetic studies within and among the Thinopyrum species (populations) carrying E and/or St genomes in the future.

New insight into the function of wheat glutenin proteins as investigated with two series of genetic mutants

Among the three major food crops (rice, wheat and maize), wheat is unique in accumulating gluten proteins in its grains. Of these proteins, the high and low molecular weight glutenin subunits (HMW-GSs and LMW-GSs) form glutenin macropolymers that are vital for the diverse end-uses of wheat grains. In this work, we developed a new series of deletion mutants lacking one or two of the three Glu-1 loci (Glu-A1, -B1 and -D1) specifying HMW-GSs. Comparative analysis of single and double deletion mutants reinforced the suggestion that Glu-D1 (encoding the HMW-GSs 1Dx2 and 1Dy12) has the largest effects on the parameters related to gluten and dough functionalities and breadmaking quality. Consistent with this suggestion, the deletion mutants lacking Glu-D1 or its combination with Glu-A1 or Glu-B1 generally exhibited strong decreases in functional glutenin macropolymers (FGMPs) and in the incorporation of HMW-GSs and LMW-GSs into FGMPs. Further examination of two knockout mutants missing 1Dx2 or 1Dy12 showed that 1Dx2 was clearly more effective than 1Dy12 in promoting FGMPs by enabling the incorporation of more HMW-GSs and LMW-GSs into FGMPs. The new insight obtained and the mutants developed by us may aid further research on the control of wheat end-use quality by glutenin proteins.

Development of a new set of molecular markers for examining Glu-A1 variants in common wheat and ancestral species

In common wheat (Triticum aestivum L.), allelic variations of Glu-A1 locus have important influences on grain end-use quality. Among the three Glu-A1 alleles, Glu-A1a and -A1b encode the high-molecular-weight glutenin subunits (HMW-GSs) 1Ax1 and 1Ax2*, respectively, whereas Glu-A1c does not specify any subunit. Here, we detected a total of 11 Glu-A1 locus haplotypes (H1 to H11) in three wheat species, by developing and using a new set of DNA markers (Xrj5, Xid3, Xrj6, Xid4 and Xrj7). The main haplotypes found in the diploid wheat T. urartu were H1, H4, H5 and H6, with H1 and H4 expressing both 1Ax and 1Ay subunits. The major haplotypes revealed for tetraploid wheat (T. turgidum) were H1, H8 and H9, with the lines expressing both 1Ax and 1Ay belonging to H1, H4 or H7. Four major haplotypes (H1, H9, H10 and H11) were discovered in common wheat, with Glu-A1a associated with H1 and H8, Glu-A1b with H10 or H11, and Glu-A1c with H9. The Glu-A1 locus haplotypes and the new set of DNA markers have potential to be used for more effectively studying and utilizing the molecular variations of Glu-A1 to improve the end-use quality of common wheat are discussed.

Rapid Development of Glu-1 Locus Near-isogenic Introgression Lines Using HMW-GS Deletion Mutant

Wheat (Triticum aestivum L., AABBDD) high molecular weight glutenin subunits (HMW-GS) were encoded by the genes located in Glu-A1, Glu-B1, and Glu-D1 loci. Evaluation and optimization of the combination of HMW-GS are very important to understand Glu-1 functions. In this study, we constructed a HMW-GS deletion mutant, DLGlu1 with Xiaoyan 81 background, and crossed it with Glenlea, a Canada elite wheat variety with superior end-use quality. Combining the technologies of wheat embryo culture and molecular marker-assisted selection (MAS), we obtained seven introgression lines containing Glenlea Glu-A1a, Glu-B1al, and Glu-D1d loci, which can be developed as a complete set of near-isogenic introgression lines possessing Glenlea different HMW-GS genes. Our study indicated that the Glu-1 deletion mutant DLGlu1 is of great value in the fast development of Glu-1 near-isogenic introgression lines and the study and utility of wheat Glu-1.