Abstract

Kernel texture is an important trait in cereals, especially wheat (Triticum spp.). Throughout the Triticeae, the puroindoline genes act to soften kernel endosperm. Absence or mutation of either or both of the two puroindolines, ‘a’ and ‘b’, inTriticum aestivum results in harder grain texture. Apparently only one puroindoline haplotype was contributed by theAegilops tauschii variety that contributed the D-genome during allopolyploidization. Yet, world collections ofAe. tauschii exhibit a range of puroindoline sequence polymorphisms. Consequently, these genes, through synthetic hexaploids (× Aegilotriticum) can enrich the wheat gene pool. Lastly, the puroindolines represent a useful tool for phylogenetic analyses. Here we review original sequence data published and/or available in public databases to reconcile the known gene sequence polymorphisms with a systematic approach to the designating of puroindoline gene and allele symbols inT. aestivum,Ae. tauschii, and × Aegilotriticum. This system follows the recommendations adopted by the International Wheat Genetics Symposium and described in the Catalogue of Gene Symbols for Wheat. Errors, discrepancies and ambiguities in the puroindolines are reviewed; a reconciliation of all existing data is outlined.

Grain texture is one of the characteristics of bread wheat (Triticum aestivum L.) quality and has an important influence on wheat milling and processing quality. Puroindoline gene, mainly controlling grain texture of bread wheat, locates on the short arm of dismal 5D chromosome and is divided into Pina and Pinb genes tightly linking together. Pina and Pinb with the coding sequence of 447 bp have no any intron and form the basis of molecular genetics of grain texture in bread wheat. Up to now, lots of haplotypes of Pina and Pinb genes have been identified in bread wheat and Aegilops tauschii. Of them, Pina-D1b allele with hardest grain texture among the known haplotypes has been found to possess a large 15 380 bp deletion beginning after nt 23 inside of Pina coding sequence in comparison with the wild type. Besides the obvious influence on grain texture, puroindoline gene plays a significant role on other aspects of wheat quality so that some Pina and Pinb alleles have significantly different quality characteristics, e.g. Pinb-D1b have slightly superior quality of steamed bread, pan bread and Chinese noodles to Pina-D1b. Gsp-1 gene tightly linking with Pina and Pinb possesses more haplotypes than puroindoline genes while has no significant effect on grain texture according to lots of reports so far. Pinb-2v genes with approximate 70% identity to Pinb gene at the DNA level have been found to possess four variants very recently that locate on 7A, 7B and 7D chromosome, respectively, which play a minor role in controlling grain texture. This study has further provided useful information on understanding the molecular basis of grain texture and Chinese wheat improvement.

籽粒硬度是重要的小麦品质性状之一,对小麦的磨粉品质和加工品质有重要影响。控制籽粒硬度的 主效基因puroindoline位于5D染色体的短臂上,可分为Pina和Pinb 2种类型。Pina和Pinb紧密连锁,编 码区均为447个碱基,没有内含子,共同形成小麦籽粒硬度的分子遗传基础。目前,普通小麦和山羊草中均已发现多种puroindoline变异类型,其中引起小麦籽粒硬度大幅度升高的Pina-D1b类型的分子机制为从编码区第23个碱基开始缺失15 380个碱基。Puroindoline除了对小麦籽粒硬度有重要影响之外,对其它品质性状也有重要影响,不同puroindoline变异类型之间小麦品质具有一定差异。另外,与puroindoline紧密连锁的Gsp-1基因变异类型更为丰富,但对籽粒硬度没有明显的调节作用。最近发现的与puroindoline b高度同源的基因Pinb-2v具有4种类型,分别位于小麦7A、7B和7D染色体上,可能对籽粒硬度具有微效的调节作用。本文通过对puroindoline的分子特征和突变类型以及相关功能进行分析和总结,旨在为中国小麦品质的基因工程改良提供参考。

Abstract

Understanding the effects of different alleles at the puroindoline b (Pinb) locus on processing quality will provide crucial information for quality improvement. Seven near-isogenic lines (NILs) planted at two locations in the 2008 cropping season were used to determine the effect of puroindoline b alleles on milling performance and Chinese raw white noodle (CRWN) quality. ThePina-D1b/Pinb-D1a genotype possessed significantly higher values in grain hardness, protein content and starch damage than other genotypes, whereas thePina-D1a/Pinb-D1d genotype had the lowest grain hardness and starch damage, with higher break flour yield, and less reduction flour yield, higher flour colour L*, and lower flour colour b*, than other genotypes. Farinograph parameters, except for water absorption, were not significantly affected by variation of puroindoline b alleles.Pina-D1a/Pinb-D1e had the highest peak viscosity, whereas the lowest value was observed in aPina-D1b/Pinb-D1a genotype. For CRWN quality, higher noodle viscoelasticity was obtained in the genotypePina-D1a/Pinb-D1e andPina-D1a/Pinb-D1g, whereasPina-D1a/Pinb-D1d had a lower smoothness score. Genotypes withPina-D1a/Pinb-D1e andPina-D1a/Pinb-D1g produced the best total noodle score. It was concluded that genotypePina-D1a/Pinb-D1d had better milling qualities, whereasPina-D1a/Pinb-D1e andPina-D1a/Pinb-D1g had slightly superior CRWN qualities in comparison with other genotypes.

Abstract

Two trials with a total of 75 spring bread wheat cultivars and advanced lines, were used to evaluate single kernel characterization system hardness, puroindoline alleles, milling yield, flour ash content, flour colour, and end-use qualities for Chinese noodles, steamed bread and pan bread. The results indicated that all International Maize and Wheat Improvement Center hard wheat lines surveyed werePina-D1b genotype, whereasPinb-D1b was the most common allele in the remaining cultivars. Genotypes withPinb-D1b possess significantly lower flour ash content and higher milling yield than those of genotypes withPina-D1b. For steamed bread, mean scores for loaf volume, crumb colour, width, structure and total score ofPinb-D1b genotypes were significantly higher than those of genotypes withPina-D1b and wild type. For Chinese fresh white noodles, means for noodle a*, colour score, viscoelasticity and total score withPinb-D1b were significantly higher than those ofPina-D1b and wild type. Means of loaf volume, texture and total score forPinb-D1b genotypes were significantly higher than those ofPina-D1b genotypes. This study further illustrated the superiority of thePinb-D1b allele on milling and processing qualities for various end products and provides useful information for wheat quality improvement.

Abstract

Transcripts encoding three novel variant forms of puroindoline b have been identified in developing seeds of wheat. These show 57–60% sequence identity with the wild type form of Pin b but all lack one of the three tryptophan residues present in the “tryptophan loop” region of the wild type protein. Counts of ESTs and array analysis indicate that the transcripts encoding variant forms of Pin b are about an order of magnitude less abundant than those encoding wild type Pin b while array analysis also shows that expression of the variant form 1 declines more rapidly than that of the wild type form during the later stages of grain development. The gene(s) encoding variant form 1, namedPinb-A2, were mapped to the long arm of chromosome 7A of bread wheat where they show linkage to novel QTLs for hardness which have been identified in two doubled haploid populations derived from crosses between hard parental cultivars (Shamrock × Shango, Malacca × Charger).

Abstract

A total of 169 wheat (Triticum aestivum L.) varieties (landraces and cultivars) were used to asses the relationship betweenPuroindoline D1 alleles andPuroindoline b-B2 variants and grain hardness, other grain traits, yield components, and flag leaf size. Results indicated that the average SKCS hardness ofPinb-B2v3 varieties was significantly greater than that ofPinb-B2v2 varieties within the softPuroindoline D1 haplotype sub-group. Conversely, no statistically significant difference was obtained for SKCS hardness between varieties with thePinb-B2v3 vs.Pinb-B2v2 alleles within the two hardPuroindoline D1 haplotypes (Pinb-D1b andPinb-D1p sub-groups). Therefore, thePuroindoline b-B2 gene may have a bigger impact on soft wheat varieties than hard. Across all varieties, thousand-kernel weight, grain weight per spike, grain diameter, grain number per spike, flag leaf width and area ofPinb-B2v3 varieties were significantly greater than those possessingPinb-B2v2. These results indicated that thePinb-B2v3 allele was associated with preferable grain yield traits compared to thePinb-B2v2 allele in bread wheat. This study provides evocative information for better understanding the molecular and genetic basis of wheat grain yield.

Abstract

While the commercially important trait of grain hardness in wheat is largely determined by the puroindoline proteins, a number of studies suggest additional loci, and a role for the grain softness protein-1 (GSP-1), encoded by the geneGsp-1 tightly linked to thepuroindoline genes, remains ambiguous. To investigate their role individualGsp-1 genes were cloned from several accessions of durum, diploid and hexaploid wheat, rather than sequencing of genomic DNA PCR products. Analysis of clones identified >1 restriction fragment length polymorphisms (RFLPs) in some 2n progenitors, >2 RFLP types in several durums and >3 in common wheat. DNA sequencing identified 30 differentGsp-1 haplotypes from various 2n, 4n and 6n wheats, exhibiting extensive single nucleotide polymorphisms (SNPs) and a 3-base deletion, all but three haplotypes being novel. Shared SNPs between various diploids, indicated an ancient origin of this gene family, but certain aspects were unique to durums, and existence of multigenes in at least some genomes was confirmed through single plant analysis of select accessions ofAegilops speltoides, durum and common wheat. Most interestingly, despite the great sequence diversity, the functionally important amino acids involved in lipid binding, i.e., the 10 cysteines and two tryptophans, were retained in all putative proteins. The results suggest that these genes may be functionally important, particularly in durums which lack puroindolines, and may have major roles in plant defence and only a minor influence on grain texture.