Identification of candidate MYB transcription factors that influence CslF6 expression in barley grain

Comparative genomics analysis of the MYB gene family in barley: preliminary insights into evolution and biological function in Blue Qingke

Background

The Myeloblastosis related (MYB) family is one of the most widely distributed transcription factor families in plants and plays a significant role in plant growth and development, hormone signal transduction, and stress response. There are many reports on MYB family species, but the research on Qingke is still limited.

Methods

This study used comparative genomics methods to analyze gene and protein structure, protein physicochemical properties, chromosome localization, and evolution. A bioinformatics approach was used to systematically analyze the HvMYB gene family. At the milk stage, soft dough stage, and mature stage, White and Blue Qingke grains were selected for RNA sequencing (RNA-seq), among which two proteins interacted (HvMYB and HvMYC). The expression of this gene family was analyzed through RNA-seq, and the expression levels of HvMYB and HvMYC in the grains of two different color varieties were analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Finally, the interaction between HvMYB and HvMYC was verified by bimolecular fluorescence complementation (BiFC) experiments.

Results

A total of 92 Qingke HvMYB genes were identified and analyzed, and 92 HvMYB proteins were classified into five categories. Cis-acting elements associated with abscisic acid response, light response, and methyl jasmonate (MeJA) response were found in the promoter regions of most MYB genes. Using qRT-PCR combined with RNA-seq analysis showed that MYB gene was highly expressed in the soft dough stage and was varietal specific. Subcellular localization indicated that HvMYB was located in the nucleus and cell membrane, HvMYC was located in the nucleus, cell membrane, and cytoplasm. Through BiFC analysis, it has been proven that HvMYB in the MYB family and HvMYC in the basic helix-loop-helix (bHLH) family can interact. This study provides a preliminary theoretical basis for understanding the function and role of the Qingke MYB gene family and provides a reference for the molecular mechanism of Qingke gene evolution.

Characterization of a near isogenic barley line with high grain β-amylase activity reveals a separation in the tight co-regulation of B-hordeins (Hor2) with endosperm-specific β-amylase (Bmy1)

GSHO 2096 is a near isogenic barley line with extremely high grain β-amylase activity, a desirable trait in the malting and brewing industry. High levels of grain β-amylase activity are caused by a surge in endosperm-specific β-amylase (Bmy1) gene expression during the early stages of grain development with high expression levels persisting throughout development. Origins of the high β-amylase activity trait are perplexing considering GSHO 2096 is not supposed to have grain β-amylase activity. GSHO 2096 is reported to be derived from a Bowman x Risø 1508 cross followed by recurrent backcrossing to Bowman (BC5). Risø 1508 carries a mutated form of the barley prolamin binding factor, which is responsible for Bmy1 expression during grain development. Thus, the pedigree of GSHO 2096 was explored to determine the potential origins of the high grain β-amylase trait. Genotyping using the barley 50k iSelect SNP array revealed Bowman and GSHO 2096 were very similar (95.4 %) and provided evidence that both Risø 56 and 1508 are in the pedigree. Risø mutants 56 and 1508 both have perturbed hordein gene expression leading to a discernable pattern using SDS-PAGE. GSHO 2096 and Risø 56 have the same hordein pattern whereas Bowman and Risø 1508 have unique patterns. RNAseq revealed that Hor2 (B-hordein) gene expression was completely downregulated making it unique as the only known line with Bmy1 expression without Hor2 co-expression. Regardless of pedigree, GSHO 2096 remains an extremely valuable high β-amylase activity line with potential utilization in breeding for malt quality.

Characterization of barley (Horduem vulgare) lys3 mutants identifies genes under the regulation of the prolamin-box binding transcription factor and elucidates its role in endosperm promoter methylation during grain development

Barley ranks fourth in global cereal production and is primarily grown for animal feed and malt. Hordeins, the principal barley seed storage proteins, are homologous to wheat gluten and when ingested elicit an immune response in people with Coeliac disease. Risø 1508 is a chemically induced barley mutant with low hordein levels imparted by the lys3.a locus that is reported to be caused by an SNP in the barley prolamin-box binding factor gene (BPBF). Reports suggest the lys3.a locus prevents CG DNA demethylation at the Hor2 (B-hordein) promoter during grain development subsequently causing hypermethylation and inhibiting gene expression. In lys3.a mutants, endosperm-specific β-amylase (Bmy1) and Hor2 are similarly downregulated during grain development and thus we hypothesize that the inability to demethylate the Bmy1 promoter CG islands is also causing Bmy1 downregulation. We use whole-genome bisulfite sequencing and mRNA-seq on developing endosperms from two lys3.a mutants and a lys3.b mutant to determine all downstream genes affected by lys3 mutations. RNAseq analysis identified 306 differentially expressed genes (DEGs) shared between all mutants and their parents and 185 DEGs shared between both lys3.a mutants and their parents. Global DNA methylation levels and promoter CG DNA methylation levels were not significantly different between the mutants and their parents and thus refute the hypothesis that the lys3.a mutant's phenotype is caused by dysregulation of demethylation during grain development. The majority of DEGs were downregulated (e.g., B- and C-hordeins and Bmy1), but some DEGs were upregulated (e.g., β-glucosidase, D-hordein) suggesting compensatory effects and potentially explaining the low β-glucan phenotype observed in lys3.a germplasm. These findings have implications on human health and provide novel insight to barley breeders regarding the use of BPBF transcription factor mutants to create gluten-free barley varieties.

Genetic Approaches to Increase Arabinoxylan and β-Glucan Content in Wheat

Wheat is one of the three staple crops feeding the world. The demand for wheat is ever increasing as a relatively good source of protein, energy, nutrients, and dietary fiber (DF) when consumed as wholemeal. Arabinoxylan and β-glucan are the major hemicelluloses in the cell walls and dietary fiber in wheat grains. The amount and structure of DF varies between grain tissues. Reducing post-prandial glycemic response as well as intestinal transit time and contribution to increased fecal bulk are only a few benefits of DF consumption. Dietary fiber is fermented in the colon and stimulates growth of beneficial bacteria producing SCFA, considered responsible for a wide range of health benefits, including reducing the risk of heart disease and colon cancer. The recommended daily intake of 25-30 g is met by only few individuals. Cereals cover nearly 40% of fiber in the Western diet. Therefore, wheat is a good target for improving dietary fiber content, as it would increase the fiber intake and simultaneously impact the health of many people. This review reflects the current status of the research on genetics of the two major dietary fiber components, as well as breeding approaches used to improve their quantity and quality in wheat grain.

An Agrobacterium-Mediated Transient Expression Method for Functional Assay of Genes Promoting Disease in Monocots

Agrobacterium-mediated transient expression (AMTE) has been widely used for high-throughput assays of gene function in diverse plant species. However, its application in monocots is still limited due to low expression efficiency. Here, by using histochemical staining and a quantitative fluorescence assay of β-glucuronidase (GUS) gene expression, we investigated factors affecting the efficiency of AMTE on intact barley plants. We found prominent variation in GUS expression levels across diverse vectors commonly used for stable transformation and that the vector pCBEP produced the highest expression. Additionally, concurrent treatments of plants with one day of high humidity and two days of darkness following agro-infiltration also significantly increased GUS expression efficiency. We thus established an optimized method for efficient AMTE on barley and further demonstrated its efficiency on wheat and rice plants. We showed that this approach could produce enough proteins suitable for split-luciferase assays of protein-protein interactions on barley leaves. Moreover, we incorporated the AMTE protocol into the functional dissection of a complex biological process such as plant disease. Based on our previous research, we used the pCBEP vector to construct a full-length cDNA library of genes upregulated during the early stage of rice blast disease. A subsequent screen of the library by AMTE identified 15 candidate genes (out of ~2000 clones) promoting blast disease on barley plants. Four identified genes encode chloroplast-related proteins: OsNYC3, OsNUDX21, OsMRS2-9, and OsAk2. These genes were induced during rice blast disease; however, constitutive overexpression of these genes conferred enhanced disease susceptibility to Colletotrichum higginsianum in Arabidopsis. These observations highlight the power of the optimized AMTE approach on monocots as an effective tool for facilitating functional assays of genes mediating complex processes such as plant-microbe interactions.