Deciphering the transcriptional regulation and spatiotemporal distribution of immunity response in barley to Pyrenophora graminea fungal invasion

Light Drives and Temperature Modulates: Variation of Phenolic Compounds Profile in Relation to Photosynthesis in Spring Barley

Accumulation and metabolic profile of phenolic compounds (PheCs; serving as UV-screening pigments and antioxidants) as well as carbon fixation rate (A_n) and plant growth are sensitive to irradiance and temperature. Since these factors are naturally co-acting in the environment, it is worthy to study the combined effects of these environmental factors to assess their possible physiological consequences. We investigated how low and high irradiance in combination with different temperatures modify the metabolic profile of PheCs and expression of genes involved in the antioxidative enzyme and PheCs biosynthesis, in relation to photosynthetic activity and availability of non-structural carbohydrates (NSC) in spring barley seedlings. High irradiance positively affected A_n, NSC, PheCs content, and antioxidant activity (AOX). High temperature led to decreased A_n, NSC, and increased dark respiration, whilst low temperature was accompanied by reduction of UV-A shielding but increase of PheCs content and AOX. Besides that, irradiance and temperature caused changes in the metabolic profile of PheCs, particularly alteration in homoorientin/isovitexin derivatives ratio, possibly related to demands on AOX-based protection. Moreover, we also observed changes in the ratio of sinapoyl-/feruloyl- acylated flavonoids, the function of which is not yet known. The data also strongly suggested that the NSC content may support the PheCs production.

Regulation of Phenolic Compound Production by Light Varying in Spectral Quality and Total Irradiance

Photosynthetically active radiation (PAR) is an important environmental cue inducing the production of many secondary metabolites involved in plant oxidative stress avoidance and tolerance. To examine the complex role of PAR irradiance and specific spectral components on the accumulation of phenolic compounds (PheCs), we acclimated spring barley (Hordeum vulgare) to different spectral qualities (white, blue, green, red) at three irradiances (100, 200, 400 µmol m⁻² s⁻¹). We confirmed that blue light irradiance is essential for the accumulation of PheCs in secondary barley leaves (in UV-lacking conditions), which underpins the importance of photoreceptor signals (especially cryptochrome). Increasing blue light irradiance most effectively induced the accumulation of B-dihydroxylated flavonoids, probably due to the significantly enhanced expression of the F3′H gene. These changes in PheC metabolism led to a steeper increase in antioxidant activity than epidermal UV-A shielding in leaf extracts containing PheCs. In addition, we examined the possible role of miRNAs in the complex regulation of gene expression related to PheC biosynthesis.

Genome Resource for Barley Leaf Stripe Pathogen Pyrenophora graminea

Pyrenophora graminea is the causative agent of barley leaf stripe disease. In this study, the strong pathogenic isolate QWC was used to generate DNA for Illumina sequencing. After assembly, its genome size was 42.5 Mb, consisting of 264 scaffolds, and a total of 10,376 genes was predicted. This is the first genome resource available for P. graminea. The genome sequences of P. graminea will accelerate the understanding interaction of P. graminea and barley.

PGPBS, a mitogen-activated protein kinase kinase, is required for vegetative differentiation, cell wall integrity, and pathogenicity of the barley leaf stripe fungus Pyrenophora graminea

The high-osmolarity glycerol (HOG) signaling pathway regulates the adaptation of fungi to environmental stressors. The mitogen-activated protein kinase kinase (MAPKK) PBS2 of Saccharomyces cerevisiae serves as a scaffold protein in the HOG pathway. We characterized the pgpbs gene of Pyrenophora graminea, which encodes a MAPKK that is 56% orthologous to PBS2 of S. cerevisiae. A cloning technique based on homology was applied to amplify the pgpbs gene. Specific silent mutations then were generated in pgpbs. We evaluated the potential roles of PGPBS in the osmotic response, vegetative differentiation, cell wall integrity, drug resistance, and pathogenicity. Our findings indicated that the pgpbs coding region comprises 2075 base pairs and encodes a protein of 676 amino acids. Mutants deficient in pgpbs expression had significant reductions in vegetative growth and were sensitive to calcofluor white (CFW), an inhibitor of cell wall synthesis. Mutants also lost pathogenicity and were sensitive to an osmotic stress-inducing medium containing NaCl and sorbitol. Moreover, mutants had increased resistance to the dicarboximide fungicide iprodione and the triazole fungicide tebuconazole. These findings suggest that pgpbs is involved in the osmotic and ionic stress responses, vegetative differentiation, cell wall integrity, virulence, and tolerance to iprodione and tebuconazole. We expect that our findings will help elucidate the pathogenesis of barley leaf stripe and will inform strategies for breeding resistance to this disease.

cDNA-AFLP analysis of transcripts induced in chickpea plants by TiO2 nanoparticles during cold stress

We evaluated the effect of TiO₂ nanoparticles (NPs) on cold tolerance (CT) development in two chickpea (Cicer arietinum L.) genotypes (Sel96Th11439, cold tolerant, and ILC533, cold susceptible) by using cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique during the first and sixth days of cold stress (CS) at 4 °C. Selective amplification by primer combinations generated 4200 transcript-derived fragments (TDFs) while 100 of them (2.62%) were differentially expressed. During CS, 60 differentially expressed TDFs of TiO₂ NPs-treated plants were cloned and 10 of them produced successfully readable sequences. These data represented different groups of genes involved in metabolism pathways, cellular defense, cell connections and signaling, transcriptional regulation and chromatin architecture. Two out of 10 TDFs were unknown genes with uncharacterized functions or sequences without homology to known ones. The network-based analysis showed a gene-gene relationship in response to CS. Quantitative reverse-transcriptase polymerase chain reaction (qPCR) confirmed differential expression of identified genes (six out of 10 TDFs) with potential functions in CT and showed similar patterns with cDNA-AFLP results. An increase in transcription level of these TDFs, particularly on the first day of CS, was crucial for developing CT through decreasing electrolyte leakage index (ELI) content in tolerant plants compared to susceptible ones, as well as in TiO₂ NPs-treated plants compared to control ones. It could also indicate probable role of TiO₂ NPs against CS-induced oxidative stress. Therefore, a new application of TiO₂ NPs in CT development is suggested for preventing or controlling the damages in field conditions and increasing crop productivity.