Puroindoline A-gene expression is involved in association of puroindolines to starch

An Overview of Factors Affecting the Functional Quality of Common Wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L.) is one of the most important crops worldwide, and, as a resilient cereal, it grows in various climatic zones. Due to changing climatic conditions and naturally occurring environmental fluctuations, the priority problem in the cultivation of wheat is to improve the quality of the crop. Biotic and abiotic stressors are known factors leading to the deterioration of wheat grain quality and to crop yield reduction. The current state of knowledge on wheat genetics shows significant progress in the analysis of gluten, starch, and lipid genes responsible for the synthesis of the main nutrients in the endosperm of common wheat grain. By identifying these genes through transcriptomics, proteomics, and metabolomics studies, we influence the creation of high-quality wheat. In this review, previous works were assessed to investigate the significance of genes, puroindolines, starches, lipids, and the impact of environmental factors, as well as their effects on the wheat grain quality.

Construction of a novel Wheat 55 K SNP array-derived genetic map and its utilization in QTL mapping for grain yield and quality related traits

Wheat is one of the most important staple crops for supplying nutrition and energy to people world. A new genetic map based on the Wheat 55 K SNP array was constructed using recombinant inbred lines derived from a cross between Zhongkemai138 and Kechengmai2 to explore the genetic foundation for wheat grain features. This new map covered 2,155.72 cM across the 21 wheat chromosomes with 11,455 markers. And 2,846 specific markers for this genetic map and 148 coincident markers among different maps were documented, which was helpful for improving and updating wheat genetic and genomic information. Using this map, a total of 68 additive QTLs and 82 pairs of epistatic QTLs were detected for grain features including yield, nutrient composition, and quality-related traits by QTLNetwork 2.1 and IciMapping 4.1 software. Fourteen additive QTLs and one pair of epistatic QTLs could be detected by both software programs and thus regarded as stable QTLs here, all of which explained higher phenotypic variance and thus could be utilized for wheat grain improvement. Additionally, thirteen additive QTLs were clustered into three genomic intervals (C4D.2, C5D, and C6D2), each of which had at least two stable QTLs. Among them, C4D.2 and C5D have been attributed to the famous dwarfing gene Rht2 and the hardness locus Pina, respectively, while endowed with main effects on eight grain yield/quality related traits and epistatically interacted with each other to control moisture content, indicating that the correlation of involved traits was supported by the pleotropic of individual genes but also regulated by the gene interaction networks. Additionally, the stable additive effect of C6D2 (QMc.cib-6D2 and QTw.cib-6D2) on moisture content was also highlighted, potentially affected by a novel locus, and validated by its flanking Kompetitive Allele-Specific PCR marker, and TraesCS6D02G109500, encoding aleurone layer morphogenesis protein, was deduced to be one of the candidate genes for this locus. This result observed at the QTL level the possible contribution of grain water content to the balances among yield, nutrients, and quality properties and reported a possible new locus controlling grain moisture content as well as its linked molecular marker for further grain feature improvement.

Molecular and physical characterization of grain hardness in European spring common wheat (Triticum aestivum L.)

Grain hardness is the single most important trait in determining technological properties and end-use quality of wheat product. This trait is controlled by two genes (Pina-D1 and Pinb-D1) at the Hardness (Ha) locus. Soft endosperm kernels are characterized by the presence of alleles 'a' in both genes (Pina-D1a and Pinb-D1a), while the medium hard and hard grain is the result of deletion in the Pina-D1 gene or single mutation of the Pinb-D1 gene. The aim of the current study was to determine the relationship between common wheat grain hardness and the presence of puroindoline genes. Eighty-one spring common wheat cultivars from Europe were analysed for grain hardness by SKCS (Single Kernel Characterization System) and Pin-D1 genes. The analysed genotypes were divided into three hardness classes: hard, medium and soft and they showed four allelic combinations in Pin-D1 genes. The SKCS results showed that hard wheat was the major type in European cultivars, whereas molecular analysis showed differential allelic combinations of puroindoline genes among these classes. The conducted analyses suggest that another major gene or other factors were influencing kernel texture.

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The online version contains supplementary material available at 10.1007/s13205-021-02897-3.

Expression and purification of recombinant puroindoline A protein in Escherichia coli and its antifungal effect against Aspergillus flavus

Aspergillus flavus is the main cause of postharvest agricultural commodity loss. In this study, puroindoline A (PINA) protein was expressed in Escherichia coli, purified, and its antifungal properties against A. flavus were characterized. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the molecular weight of the recombinant PINA protein was approximately 44 kDa. PINA exerted a powerful antifungal effect against A. flavus at 42.42 μg/mL on potato dextrose agar culture medium. Flow cytometry and scanning electron microscopy revealed that the spore morphology was damaged by PINA exposure; spores were depressed and broken, suggesting that the cell wall was impaired. Transmission electron microscopy and propidium iodide staining illustrated significant changes in intracellular spore structure, indicating cell membrane damage. 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine iodide staining indicated decreased mitochondrial membrane potential. Large nuclear condensation and DNA fragmentation were detected by 4',6-diamidino-2-phenylindole staining. The expression of genes related to the cell wall, cell membrane, and spore germination significantly changed in PINA-treated cells; this illustrated the probable mode of PINA action on A. flavus through cell wall destruction and triggered cell membrane, mitochondrial, and DNA damage leading to cell death. The antifungal mechanism of wheat PINA protein on A. flavus has been demonstrated in this study, and has potential application in preventing postharvest loss in the agricultural industry.

Influence of Gene Expression on Hardness in Wheat

Puroindoline (Pina and Pinb) genes control grain texture or hardness in wheat. Wild-type/soft alleles lead to softer grain while a mutation in one or both of these genes results in a hard grain. Variation in hardness in genotypes with identical Pin alleles (wild-type or mutant) is known but the molecular basis of this is not known. We now report the identification of wheat genotypes with hard grain texture and wild-type/soft Pin alleles indicating that hardness in wheat may be controlled by factors other than mutations in the coding region of the Pin genes. RNA-Seq analysis was used to determine the variation in the transcriptome of developing grains of thirty three diverse wheat genotypes including hard (mutant Pin) and soft (wild type) and those that were hard without having Pin mutations. This defined the role of pin gene expression and identified other candidate genes associated with hardness. Pina was not expressed in hard wheat with a mutation in the Pina gene. The ratio of Pina to Pinb expression was generally lower in the hard non mutant genotypes. Hardness may be associated with differences in Pin expression and other factors and is not simply associated with mutations in the PIN protein coding sequences.

Wheat (Triticum aestivum L. and T. turgidum L. ssp. durum) Kernel Hardness: I. Current View on the Role of Puroindolines and Polar Lipids

Wheat hardness has major consequences for the entire wheat supply chain from breeders and millers over manufacturers to, finally, consumers of wheat-based products. Indeed, differences in hardness among Triticum aestivum L. or between T. aestivum L. and T. turgidum L. ssp. durum wheat cultivars determine not only their milling properties, but also the properties of flour or semolina endosperm particles, their preferential use in cereal-based applications, and the quality of the latter. Although the mechanism causing differences in wheat hardness has been subject of research more than once, it is still not completely understood. It is widely accepted that differences in wheat hardness originate from differences in the interaction between the starch granules and the endosperm protein matrix in the kernel. This interaction seems impacted by the presence of either puroindoline a and/or b, polar lipids on the starch granule surface, or by a combination of both. We focus here on wheat hardness and its relation to the presence of puroindolines and polar lipids. More in particular, the structure, properties, and genetics of puroindolines and their interactions with polar lipids are critically discussed as is their possible role in wheat hardness. We also address future research needs as well as the presence of puroindoline-type proteins in other cereals.

The RNA-mediated silencing of one of the Pin genes in allohexaploid wheat simultaneously decreases the expression of the other, and increases grain hardness

The RNAi-mediated silencing of Pina and Pinb, the two genes responsible for the grain texture of allohexaploid wheat, was induced and analysed in two wheat cultivars, Kontesa and Torka. A characterization of the two genes in non-transgenic plants revealed that Pinb carries a point mutation, designated Pinb-D1c in both cultivars. This mutation does not influence transcript abundance or protein content. Two silencing cassettes of the hpRNA type were constructed and used for stable transformation via Agrobacterium. In total, 43 transgenic lines representing the two cultivars were obtained, transformed with the silencing cassettes for Pina or for Pinb or co-transformed with both cassettes. The relative transcript levels of the two genes in the same progeny plant were found to be similar, independent of the silencing cassette used. The reduction in the Pina and Pinb transcript levels in the segregating T(1) progeny of Kontesa and Torka transformed with one of the silencing cassettes exceeded 80%. Co-transformation with the silencing cassettes for both genes resulted in a reduction of over 91% of Pina and Pinb transcripts in some segregating T(1) progeny of Kontesa. The silencing was transmitted to the T(4) kernel generation of the T(3) lines. A significant reduction or lack of both puroindoline proteins in the silenced lines correlated with an essential increase in grain hardness. The discussion covers some new insights into the function of the Pin genes, including the simultaneous silencing of both, independent of the siRNA signal.

The determinants of grain texture in cereals

Kernel hardness is an important agronomic trait that influences end-product properties. In wheat cultivars, this trait is determined by the Puroindoline a (Pina) and Puroindoline b (Pinb) genes, located in the Hardness locus (Ha) on chromosome 5DS of the D genome. Wild type alleles code puroindoline a (PINA) and puroindoline b (PINB) proteins, which form a 15-kDa friabilin present on the surface of water-washed starch granules. Both the proteins are accumulated in the starch endosperm cells and aleurone of the mature kernels. Puroindoline-like genes coding puroindoline-like proteins in the starch endosperm occur in some of the genomes of Triticeae and Aveneae cereals. Orthologs are present in barley, rye and oats. However, some genomes of these diploid and polyploid cereals, like that of Triticum turgidum var. durum (AABB) lack the puroindoline genes, having a very hard kernel texture. The two wild type alleles in opposition (dominant loci) control the soft phenotype. Mutation either in Pina or Pinb or in both leads to a medium-hard or hard kernel texture. The most frequent types of Pin mutations are point mutations within the coding sequence resulting in the substitution of a single amino acid or a null allele. The latter is the result of a frame shift determined by base deletion or insertion or a one-point mutation to the stop codon. The lipid-binding properties of the puroindolines affect not only the dough quality but also the plants' resistance to pathogens. Genetic modification of cereals with Puroindoline genes and/or their promoters enable more detailed functional analyses and the production of plants with the desired characteristics.

Molecular genetics of puroindolines and related genes: regulation of expression, membrane binding properties and applications

Kernel texture of wheat is a primary determinant of its technological properties. Soft kernel texture phenotype results when the Puroindoline a and Puroindoline b genes are present and encode the wild-type puroindolines PINA and PINB, respectively, and various mutations in either or both gene(s) result in hard phenotypes. A wealth of information is now available that furthers our understanding regarding the spatial and temporal regulation of expression of Puroindoline genes. Through the use of model membranes and synthetic peptides we also have a clearer understanding of the significance of the cysteine backbone, the tryptophan-rich domain (TRD) and the helicoid tertiary structures of PIN proteins in relation to their membrane-active properties. Many studies suggest individual yet co-operative modes of action of the PIN proteins in determining kernel texture, and significant evidence is accumulating that the proteins have in vivo and in vitro antimicrobial activities, shedding light on the biological roles of this unique ensemble of proteins. The puroindolines are now being explored for grain kernel texture modifications as well as antimicrobial activities.

Analysis of the wheat endosperm transcriptome

Among the cereals, wheat is the most widely grown geographically and is part of the staple diet in much of the world. Understanding how the cereal endosperm develops and functions will help generate better tools to manipulate grain qualities important to end-users. We used a genomics approach to identify and characterize genes that are expressed in the wheat endosperm. We analyzed the 17,949 publicly available wheat endosperm EST sequences to identify genes involved in the biological processes that occur within this tissue. Clustering and assembly of the ESTs resulted in the identification of 6,187 tentative unique genes, 2,358 of which formed contigs and 3,829 remained as singletons. A BLAST similarity search against the NCBI non-redundant sequence database revealed abundant messages for storage proteins, putative defense proteins, and proteins involved in starch and sucrose metabolism. The level of abundance of the putatively identified genes reflects the physiology of the developing endosperm. Half of the identified genes have unknown functions. Approximately 61% of the endosperm ESTs has been tentatively mapped in the hexaploid wheat genome. Using microarrays for global RNA profiling, we identified endosperm genes that are specifically up regulated in the developing grain.

Complementation of the pina (null) allele with the wild type Pina sequence restores a soft phenotype in transgenic wheat

The tightly linked puroindoline genes, Pina and Pinb, control grain texture in wheat, with wild type forms of both giving soft, and a sequence alteration affecting protein expression or function in either giving rise to hard wheat. Previous experiments have shown that addition of wild type Pina in the presence of mutated Pinb gave intermediate grain texture but addition of wild type Pinb gave soft grain. This raises questions as to whether Pina may be less functional than Pinb. Our goal here was to develop and characterize wheat lines expressing the wild type Pina-D1a sequence in hard wheat with the null mutation (Pina-D1b) for Pina. Three transgenic lines plus Bobwhite were evaluated in two environments. Grain texture, grain protein, and kernel weight were determined for the transgenic lines and Bobwhite. The three transgenic lines had soft phenotype, and none of the transgenic lines differed from Bobwhite for grain protein or kernel weight. The soft phenotype was accompanied by increases in Pina transcript accumulation. Total Triton X-114 extractable PINA and PINB increased from 2.5 to 5.5 times those from a soft wheat reference sample, and friabilin, PINA and PINB bound to starch, increased from 3.8 to 7.8 times those of the soft wheat reference. Bobwhite showed no starch bound PINA, but transgenic lines had levels from 5.3 to 13.7 times those of the soft wheat reference sample. Starch bound PINB in transgenic lines also increased from 0.9 to 2.5 times that for the soft wheat reference sample. The transgenic expression of wild type Pina sequence in the Pina null genotype gave soft grain with the characteristics of soft wheat including increased starch bound friabilin. The results support the hypothesis that both wild type Pin genes need to be present for friabilin formation and soft grain.

Cloning and expression of two plant proteins: similar antimicrobial activity of native and recombinant form

Antimicrobial peptides and proteins are being studied with increasing interest because of their broad range antimicrobial activity. Among plant antimicrobial proteins, the wheat seed polypeptides, puroindoline a and puroindoline b, are particularly interesting because of their established antibacterial activity. In this paper we describe different strategies used to clone His tagged and GST tagged puroindolines obtaining 1.5 mg recombinant protein from 1 l culture. The antimicrobial activity of recombinant and native puroindolines was comparable.

Molecular and biochemical characterization of puroindoline a and b alleles in Chinese landraces and historical cultivars

Kernel hardness that is conditioned by puroindoline genes has a profound effect on milling, baking and end-use quality of bread wheat. In this study, 219 landraces and 166 historical cultivars from China and 12 introduced wheats were investigated for their kernel hardness and puroindoline alleles, using molecular and biochemical markers. The results indicated that frequencies of soft, mixed and hard genotypes were 42.7, 24.3, and 33.0%, respectively, in Chinese landraces and 45.2, 13.9, and 40.9% in historical cultivars. The frequencies of PINA null, Pinb-D1b and Pinb-D1p genotypes were 43.8, 12.3, and 39.7%, respectively, in hard wheat of landraces, while 48.5, 36.8, and 14.7%, respectively, in historical hard wheats. A new Pinb-D1 allele, designated Pinb-D1t, was identified in two landraces, Guangtouxianmai and Hongmai from the Guizhou province, with the characterization of a glycine to arginine substitution at position 47 in the coding region of Pinb gene. Surprisingly, a new Pina-D1 allele, designated Pina-D1m, was detected in the landrace Hongheshang, from the Jiangsu province, with the characterization of a proline to serine substitution at position 35 in the coding region of Pina gene; it was the first novel mutation found in bread wheat, resulting in a hard endosperm with PINA expression. Among the PINA null genotypes, an allele designed as Pina-D1l, was detected in five landraces with a cytosine deletion at position 265 in Pina locus; while another novel Pina-D1 allele, designed as Pina-D1n, was identified in six landraces, with the characterization of an amino acid change from tryptophan-43 to a 'stop' codon in the coding region of Pina gene. The study of puroindoline polymorphism in Chinese wheat germplasm could provide useful information for the further understanding of the molecular basis of kernel hardness in bread wheat.

Two plant puroindolines colocalize in wheat seed and in vitro synergistically fight against pathogens

Puroindolines, for years largely investigated for their involvement in wheat kernel hardness, have recently attracted attention thanks to their possible role as antimicrobial proteins. With the aim to enhance our knowledge of these proteins we studied their localization in the kernel, and their antimicrobial activity in vitro against six different bacterial strains. Immunolocalization showed that both the PINs are strongly concentrated in the aleurone layer, but also highly present in the endosperm. Interestingly we observed that puroindolines not only have the same spatial distribution in the kernel, they are also always found co-localized. Their co-localization suggests that they could cooperate in defending the plant against pathogens. We therefore tested antimicrobial activity of PINA and PINB, and a putative synergism between these proteins. The results showed that the two polypeptides can in vitro inhibit growth of all the bacteria tested; furthermore when combined together they are able to enhance each other's toxicity. In view of their antimicrobial activity and of their natural presence in Triticum aestivum wheat flour, puroindolines look promising antibacterial agents and thus deserve further studies aimed at establishing their possible future applications in fields of food and health care. Since PINs were still detectable in bakery products, these proteins may be promising tools in investigating natural ways of food preservation.

A microarray analysis of wheat grain hardness

Grain hardness is an important quality characteristic of wheat grain, and considerable research effort has focused on characterising the genetic and biochemical basis underlying the hardness phenotype. Previous research has shown that the predominant difference between hard and soft seeds is linked to the puroindoline (PIN) proteins. In this study the near-isogenic lines of Heron and Falcon, which differ only in the grain hardness character, were compared using a cDNA microarray consisting of approximately 5,000 unique cDNA clones that were isolated from wheat and barley endosperm tissue. Our analysis showed that major differences in gene expression were evident for puroindoline-a (Pina), with a minor but not consistent change in the expression of puroindoline-b (Pinb). These observations were confirmed using a 16,000 unique cDNA microarray in a comparison of hard wheats with either the Pina null or Pinb mutation.

Genetic and biochemical analysis of common wheat cultivars lacking puroindoline a

Puroindoline a (Pin-a) and puroindoline b (Pin-b), two basic isoforms encoded by the Pina-D1 and Pinb-D1 loci respectively, involved in controlling grain texture in wheat, were isolated from starch granules of soft wheat cultivars using three different extraction procedures, and fractionated by acidic polyacrylamide gel electrophoresis (A-PAGE). Tris buffer containing 1% Triton X-114 extracted Pin-a and small amounts of Pin-b, whereas 1% SDS preferably extracted Pin-b. Large amounts of both puroindolines were isolated by a solution containing 50% propan-2-ol and 50 mM NaCl. This solution extracted reduced amounts of Pin-b and no traces of Pin-a from starch granules of 20 hard common wheats containing the null allele Pina-D1b. The absence of Pin-a was confirmed by immunostaining with an anti-Pin-a antiserum. With the exception of two cultivars, null Pin-a cultivars gave no PCR fragment with three primer pairs specific to either the coding region or the promoter region of Pina-D1a, suggesting that major changes had occurred at the Pina-D1 locus in these genotypes. Cultivars Fortuna and Glenman were unique in giving size-specific PCR fragments with all primer pairs for the allele Pina-D1a and showed a cytosine deletion at position 267 in the coding region of the Pin-a gene, which resulted in a TGA stop codon at position 361. However, there was no evidence of a mutated protein in the A-PAGE or SDS-PAGE patterns of Fortuna and Glenman. The novel gene, provisionally named Pina-D1c, is the first null allele due to a point mutation that has been identified at the Pina-D1 locus.

Real Time RT-PCR and flow cytometry to investigate wheat kernel hardness: role of puroindoline genes and proteins

Developing seeds from Triticum aestivum (wheat) cultivars were collected after flowering and analysed for puroindoline a and b gene expression by Real Time RT-PCR. Mature seeds were investigated for the presence and the amount of starch-associated puroindoline a and b proteins by flow cytometry. Puroindoline a gene and protein were found to have a predominant role in controlling wheat kernel hardness.