Differential RNA expression of Bmy1 during barley seed development and the association with β-amylase accumulation, activity, and total protein

Endophytic Fungi Regulate HbNHX1 Expression and Ion Balance in Hordeum bogdanii under Alkaline Stress

Plants cope with abiotic stress in several ways, including by collaborating with microorganisms. Epichloë, an endophytic fungus, has been shown to improve plant tolerance to extreme external environments. Hordeum bogdanii is a known salt-tolerant plant with the potential to improve alkaline lands. NHX1 plays a key role in the transport of ions in the cell and is overexpressed in plants with increased salt tolerance. However, the expression levels of HbNHX1 in Epichloë endophytic fungal symbionts in H. bogdanii have not been elucidated. We used Hordeum bogdanii (E+) with the endophytic fungi Epichloë bromicola and H. bogdanii (E-) without the endophytic fungi and compared the differences in the ion content and HbNHX1 expression between the shoots and roots of E+ and E- plants under alkaline stress. The absorption capacity of both K⁺ and Na⁺ of H. bogdanii with endophytic fungi was higher than that without endophytic fungi. In the absence of alkaline stress, endophytic fungi significantly reduced the Cl^- content in the host H. bogdanii. Alkaline stress reduced SO₄^2- content in H. bogdanii; however, compared with E-, endophytic fungi increased the content of SO₄^2- in E+ plants. With an increase in the alkaline concentration, the expression of HbNHX1 in the roots of H. bogdanii with endophytic fungus exhibited an upward trend, whereas the expression in the shoots exhibited a downward trend first and then an upward trend. Under 100 mmol·L^-1 mixed alkaline stress, the expression of HbNHX1 in E+ was significantly higher than that in E-, indicating that endophytic fungi could increase the Na⁺ region in vacuoles. The external environment affects the regulation of endophytic fungi in H. bogdanii and that endophytic fungi can play a key role in soil salinization. Therefore, the findings of this study will provide technical support and a theoretical basis for better utilization of endophytic fungi from H. bogdanii in saline land improvement.

Comparative transcriptome analysis of resistant and susceptible Kentucky bluegrass varieties in response to powdery mildew infection

BACKGROUND

Poa pratensis is one of the most common cold-season turfgrasses used for urban turf building, and it is also widely used in ecological environment management worldwide. Powdery mildew is a common disease of P. pratensis. To scientifically and ecologically control lawn powdery mildew, the molecular mechanism underlying the response of P. pratensis to powdery mildew infection must better understood.

RESULTS

To explore molecular mechanism underlying the response of P. pratensis to powdery mildew infection, this study compared physiological changes and transcriptomic level differences between the highly resistant variety 'BlackJack' and the extremely susceptible variety 'EverGlade' under powdery mildew infection conditions. We analyzed DEGs using reference canonical pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and the results showed that "starch and sucrose metabolism", "photosynthesis" and "fatty acid metabolism"pathways were only enriched in 'BlackJack', and the expression of DEGs such as HXK, INV, GS, SS, AGpase and β-amylase in "starch and sucrose metabolism" pathway of 'BlackJack' were closely related to powdery mildew resistance. Meanwhile, compared with 'EverGlade', powdery mildew infection promoted synthesis of sucrose, expression of photosynthesis parameters and photosynthesis-related enzymes in leaves of 'BlackJack' and decreased accumulation of monosaccharides such as glucose and fructose.

CONCLUSIONS

This study identified the key metabolic pathways of a P. pratensis variety with high resistance to powdery mildew infection and explored the differences in physiological characteristics and key genes related to sugar metabolism pathways under powdery mildew stress. These findings provide important insights for studying underlying molecular response mechanism.

Genetic Analysis and Molecular Breeding Applications of Malting Quality QTLs in Barley

Malting quality is an important determinant of the value of barley grain used in malting and brewing. With recent sequencing and assembling of the barley genome, an increasing number of quantitative trait loci (QTLs) and genes related to malting quality have been identified and cloned, which lays a good molecular genetic basis for barley quality improvement. In this review, we describe the following indicators of malting quality: malt extract (ME), diastatic power (DP), kolbach index (KI), wort viscosity (VIS), free amino nitrogen (FAN) content, soluble protein (SP) content, wort β-glucan (WBG) content, and protein content (PC), and have list related QTLs/genes with high phenotypic variation in multiple populations or environments. Meanwhile, the correlations among the quality parameters and parts of significant indicators suitable for improvement are discussed based on nutrient composition and content required for high-quality malt, which will provide reference for molecular marker-assisted selection (MAS) of malting quality in barley.

Differences in hydrolytic enzyme activity accompany natural variation in mature aleurone morphology in barley (Hordeum vulgare L.)

The aleurone is a critical component of the cereal seed and is located at the periphery of the starchy endosperm. During germination, the aleurone is responsible for releasing hydrolytic enzymes that degrade cell wall polysaccharides and starch granules, which is a key requirement for barley malt production. Inter- and intra-species differences in aleurone layer number have been identified in the cereals but the significance of this variation during seed development and germination remains unclear. In this study, natural variation in mature aleurone features was examined in a panel of 33 Hordeum vulgare (barley) genotypes. Differences were identified in the number of aleurone cell layers, the transverse thickness of the aleurone and the proportion of aleurone relative to starchy endosperm. In addition, variation was identified in the activity of hydrolytic enzymes that are associated with germination. Notably, activity of the free fraction of β-amylase (BMY), but not the bound fraction, was increased at grain maturity in barley varieties possessing more aleurone. Laser capture microdissection (LCM) and transcriptional profiling confirmed that HvBMY1 is the most abundant BMY gene in developing grain and accumulates in the aleurone during early stages of grain fill. The results reveal a link between molecular pathways influencing early aleurone development and increased levels of free β-amylase enzyme, potentially highlighting the aleurone as a repository of free β-amylase at grain maturity.

Differences in hydrolytic enzyme activity accompany natural variation in mature aleurone morphology in barley (Hordeum vulgare L.)

The aleurone is a critical component of the cereal seed and is located at the periphery of the starchy endosperm. During germination, the aleurone is responsible for releasing hydrolytic enzymes that degrade cell wall polysaccharides and starch granules, which is a key requirement for barley malt production. Inter- and intra-species differences in aleurone layer number have been identified in the cereals but the significance of this variation during seed development and germination remains unclear. In this study, natural variation in mature aleurone features was examined in a panel of 33 Hordeum vulgare (barley) genotypes. Differences were identified in the number of aleurone cell layers, the transverse thickness of the aleurone and the proportion of aleurone relative to starchy endosperm. In addition, variation was identified in the activity of hydrolytic enzymes that are associated with germination. Notably, activity of the free fraction of β-amylase (BMY), but not the bound fraction, was increased at grain maturity in barley varieties possessing more aleurone. Laser capture microdissection (LCM) and transcriptional profiling confirmed that HvBMY1 is the most abundant BMY gene in developing grain and accumulates in the aleurone during early stages of grain fill. The results reveal a link between molecular pathways influencing early aleurone development and increased levels of free β-amylase enzyme, potentially highlighting the aleurone as a repository of free β-amylase at grain maturity.

Evaluation and selection of internal reference genes from two- and six-row U.S. malting barley varieties throughout micromalting for use in RT-qPCR

Reverse transcription quantitative polymerase chain reaction (RT-qPCR) is a popular method for measuring transcript abundance. The most commonly used method of interpretation is relative quantification and thus necessitates the use of normalization controls (i.e. reference genes) to standardize transcript abundance. The most popular gene targets for RT-qPCR are housekeeping genes because they are thought to maintain a static transcript level among a variety of samples. However, more recent studies have shown, several housekeeping genes are not reliably stable. This is the first study to examine the potential of several reference genes for use in RT-qPCR normalization during barley malting. The process of malting barley mechanizes the imbibition and subsequent germination of barley seeds under controlled conditions. Malt quality is controlled by many pleiotropic genes that are determined by examining the result of physiological changes the barley seed undergoes during the malting process. We compared the stability of 13 reference genes across both two-and six-row malting barleys (Conrad and Legacy, respectfully) throughout the entirety of the malting process. Initially, primer target specificity, amplification efficiency and average Ct values were determined for each of the selected primer pairs. Three statistical programs (geNorm, NormFinder, and BestKeeper) were used to rank the stability of each reference gene. Rankings were similar between the two- and six-row with the exception of BestKeeper’s ranking of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). A consensus ranking among programs was determined using RefFinder. Our results show that Actin (ACT) and Heat Shock Protein 70 (HSP70) were the most stable throughout micromalting, while GAPDH and Cyclophilin (CYP) were the least stable. Two reference genes are necessary for stable transcript normalization according to geNorm and the best two reference genes (ACT and HSP70) provided a sufficient level of stability.

Variation in β-amylase activity and thermostability in Tibetan annual wild and cultivated barley genotypes

β-Amylase activity (BAA) and thermostability (BAT) are important traits for malt quality. In this study, 138 Tibetan annual wild barley accessions and 20 cultivated genotypes differing in BAA were planted and analyzed in 2009 and 2012. Significant differences were detected among genotypes in BAA and BAT. The cultivated genotypes had a mean BAA of 1137.6 U/g and a range of from 602.1 to 1407.5 U/g, while the wild accessions had a mean of 1517.9 U/g and a range of from 829.7 to 2310.0 U/g. The cultivated genotypes had a mean relative residual β-amylase activity (RRBAA) of 61.6% and a range of from 22.2% to 82.3%, while the wild barleys had a mean of 57.8% and a range of from 21.9% to 96.1%. Moreover, there was a significant difference among genotypes in the response of RRBAA to the temperature and duration of heat treatment. The wild barleys had wider variation in BAA and BAT than cultivated genotypes.

Discovery of novel Bmy1 alleles increasing β-amylase activity in Chinese landraces and Tibetan wild barley for improvement of malting quality via MAS

China has a large barley germplasm collection which has not been well characterized and is therefore underutilized. The Bmy1 locus encoding the β-amylase enzyme on chromosome 4H has been well characterized in the worldwide barley germplasm collections due to its importance in the malting and brewing industry. The Bmy1 locus was chosen as an indicator to understand genetic potential for improvement of malting quality in Chinese landraces and Tibetan wild barley. The genetic diversity of 91 barley accessions was assessed using allele specific Multiplex-ready molecular markers. Eight accessions were further sequenced, based on the Multiplex-ready marker diversity for Bmy1 in the germplasm. Six of the eight accessions clustered together in a unique group, and showed similarities to ‘Haruna Nijo’, wild barley accession PI296896 and ‘Ashqelon’. Sequence comparisons with the known Bmy1 alleles identified not only the existing 13 amino acid substitutions, but also a new substitution positioned at A387T from a Chinese landrace W127, which has the highest β-amylase activity. Two new alleles/haplotypes namely Bmy1-Sd1c and Bmy1-Sd5 were designated based on different amino acid combinations. We identified new amino acid combination of C115, D165, V233, S347 and V430 in the germplasm. The broad variation in both β-amylase activity and amino acid composition provides novel alleles for the improvement of malting quality for different brewing styles, which indicates the high potential value of the Chinese landraces and Tibetan wild barley.

Differential expression of two β-amylase genes (Bmy1 and Bmy2) in developing and mature barley grain

Two barley (Hordeum vulgare L.) β-amylase genes (Bmy1 and Bmy2) were studied during the late maturation phase of grain development in four genotypes. The Bmy1 and Bmy2 DNA and amino acid sequences are extremely similar. The largest sequence differences are in the introns, seventh exon, and 3' UTR. Accumulation of Bmy2 mRNA was examined in developing grain at 17, 19, and 21 days after anthesis (DAA). One genotype, PI 296897, had significantly higher Bmy2 RNA transcript accumulation than the other three genotypes at all developmental stages. All four genotypes had Bmy2 mRNA levels decrease from 17 to 19 DAA, and remain the same from 19 to 21 DAA. Levels of Bmy1 mRNA were twenty thousand to over one hundred thousand times more than Bmy2 mRNA levels in genotypes Legacy, Harrington, and Ashqelon at all developmental stages and PI 296897 at 19 and 21 DAA. PI 296897 had five thousand times more Bmy1 mRNA than Bmy2 mRNA at 17 DAA. However, Bmy2 protein was not found at 17 DAA in any genotype. The presence of Bmy2 was immunologically detected at 19 DAA and was present in greater amounts at 21 DAA. Also, Bmy2 protein was found to be stored in mature grain and localized in the soluble fraction. However, Bmy1 protein was far more prevalent than Bmy2 at all developmental stages in all genotypes. Thus, the vast majority of β-amylase activity in developing and mature grain can be attributed to endosperm-specific β-amylase.