Barley is the fourth most important cereal crop and has been domesticated and cultivated for more than 10,000 years. Breeding climate-smart and stress-tolerant cultivars is considered the most suitable way to accelerate barley improvement. However, the conventional breeding framework needs to be changed to facilitate genomics-based breeding of barley. The continuous progress in genomics has opened up new avenues and tools that are promising for making barley breeding more precise and efficient. For instance, reference genome assemblies in combination with germplasm sequencing to delineate breeding have led to the development of more efficient barley cultivars. Genetic analysis, such as QTL mapping and GWAS studies using sequencing approaches, have led to the identification of molecular markers, genomic regions and novel genes associated with the agronomic traits of barley. Furthermore, SNP marker technologies and haplotype-based GWAS have become the most applied methods for supporting molecular breeding in barley. The genetic information is also used for high-efficiency gene editing by means of CRISPR-Cas9 technology, the best example of which is the cv. Golden Promise. In this review, we summarize the genomic databases that have been developed for barley and explain how the genetic resources of the reference genome, the available state-of-the-art bioinformatics tools, and the most recent assembly of a barley pan-genome will boost the genomics-based breeding for barley improvement.

Both biotic and abiotic stresses adversely affect plant growth and development, ultimately reducing agricultural productivity. Secondary metabolites (SMs) are essential compounds that contribute to plant survival by facilitating interactions with the environment. In response to both abiotic and biotic stresses, plants synthesize and accumulate SMs, which in turn trigger signaling pathways that lead to post-transcriptional modifications within plant cells. These changes activate a series of defense mechanisms that enhance the plant's resilience and adaptation to stress. SMs are instrumental in ensuring plant survival under challenging conditions by modulating the plant's defense systems to cope with environmental threats. Beyond their role in stress tolerance, SMs are also bioactive compounds with significant economic and health value. In this review, we explore the functions of various SMs, such as alkaloids, flavonoids, and phenolic acids in defense against abiotic and biotis stresses. Additionally, we discuss the potential of harnessing SMs in the genetic improvement of crop stress tolerance, highlighting their roles in advancing agricultural sustainability.

Plants can utilize different N forms, including organic and inorganic N resources, and show great differences in the utilization efficiency of each N form among species and genotypes within a species. Previously, we found that the Tibetan wild barley genotype (XZ16) was better in the utilization of organic nitrogen in comparison with the cultivated barley genotype (Hua30). In this study, the metabolite profiles of the two barley genotypes were comprehensively compared in their response to four N forms, including nitrate (NO₃⁻), ammonium (NH₄⁺), urea, and glycine. The macro and micro nutrient concentrations in shoots were mostly found to be higher in the nitrate and urea treatments than in ammonium and glycine in both the genotypes. XZ16 had higher concentrations of nutrient ions in the glycine treatment, but Hua30 accumulated more nutrients in the ammonium treatment. Among a total of 163 differentially regulated metabolites, the highest up-regulation and highest down-regulation values were found in XZ16 in the glycine and urea treatments, respectively. Some important metabolites, such as proline, glutamine, serine, asparagine, L-homoserine, aspartic acid, putrescine, ornithine, and 4-aminobutyrate, were up-regulated in the glycine treatment in both the genotypes with a higher fold change in XZ16 than that in Hua30. Similarly, fructose-6-PO₄, aconitic acid, and isocitrate were only up-regulated in XZ16 in the glycine treatment. Here, we concluded that the genotype XZ16 exhibited a better response to the glycine treatment, while Hua30 showed a better response to the NH₄⁺ treatment, which is attributed to the better utilization of glycine-N and NH₄⁺-N, respectively.

Plants can utilize the different forms of nitrogen (N), including inorganic and organic N nutrients, and show the great difference in the utilizing efficiency of N-form among species and genotypes within a species. In our previous study, we found that Tibetan wild barley (XZ16) was better in utilization of organic nitrogen in comparison with cultivated barley (Hua30). In this study, metabolite profiles of the two barley genotypes were comprehensively compared in their response to four N forms, including nitrate (NO3-), ammonium (NH4+), urea and glycine. Macro-and micro-nutrient concentrations in shoots were mostly found higher in nitrate and urea treatments than in ammonium and glycine in both the genotypes. XZ16 had higher concentrations of nutrient ions in glycine treatment, but Hua30 accumulated more nutrients in ammonium treatment. Among the total 163 differentially expressed metabolites, highest up-regulation and highest down-regulation was found in XZ16 in glycine and urea treatments respectively. Some important metabolites such as proline, glutamine, serine, asparagine, L-homoserine, aspartic acid, putrescine, ornithine, 4-aminobutyrate were up-regulated in glycine treatment in both the genotypes with higher fold change in XZ16 than in Hua30. Similarly, fructose-6-PO4, aconitic acid and isocitrate were only up-regulated in XZ16 in glycine treatment. Here, we concluded that the genotype XZ16 exhibited higher response to glycine treatment, while Hua30 showed higher response to NH4+ treatment which is attributed to their better utilization of glycine-N and NH4+-N, respectively. .