Molecular Mechanisms of the Stripe Rust Interaction with Resistant and Susceptible Wheat Genotypes

Rust fungi cause significant damage to wheat production worldwide. In order to mitigate disease impact and improve food security via durable resistance, it is important to understand the molecular basis of host-pathogen interactions. Despite a long history of research and high agricultural importance, still little is known about the interactions between the stripe rust fungus and wheat host on the gene expression level. Here, we present analysis of the molecular interactions between a major wheat pathogen-Puccinia striiformis f. sp. tritici (Pst)-in resistant and susceptible host backgrounds. Using plants with durable nonrace-specific resistance along with fully susceptible ones allowed us to show how gene expression patterns shift in compatible versus incompatible interactions. The pathogen showed significantly greater number and fold changes of overexpressed genes on the resistant host than the susceptible host. Stress-related pathways including MAPK, oxidation-reduction, osmotic stress, and stress granule formation were, almost exclusively, upregulated in the resistant host background, suggesting the requirement of the resistance-countermeasure mechanism facilitated by Pst. In contrast, the susceptible host background allowed for broad overrepresentation of the nutrient uptake pathways. This is the first study focused on the stripe rust pathogen-wheat interactions, on the whole transcriptome level, from the pathogen side. It lays a foundation for the better understanding of the resistant/susceptible hosts versus pathogenic fungus interaction in a broader sense.

Organellomic gradients in the fourth dimension

Organelles function as hubs of cellular metabolism and elements of cellular architecture. In addition to 3 spatial dimensions that describe the morphology and localization of each organelle, the time dimension describes complexity of the organelle life cycle, comprising formation, maturation, functioning, decay, and degradation. Thus, structurally identical organelles could be biochemically different. All organelles present in a biological system at a given moment of time constitute the organellome. The homeostasis of the organellome is maintained by complex feedback and feedforward interactions between cellular chemical reactions and by the energy demands. Synchronized changes of organelle structure, activity, and abundance in response to environmental cues generate the fourth dimension of plant polarity. Temporal variability of the organellome highlights the importance of organellomic parameters for understanding plant phenotypic plasticity and environmental resiliency. Organellomics involves experimental approaches for characterizing structural diversity and quantifying the abundance of organelles in individual cells, tissues, or organs. Expanding the arsenal of appropriate organellomics tools and determining parameters of the organellome complexity would complement existing -omics approaches in comprehending the phenomenon of plant polarity. To highlight the importance of the fourth dimension, this review provides examples of organellome plasticity during different developmental or environmental situations.

Heat and drought induced transcriptomic changes in barley varieties with contrasting stress response phenotypes

Drought and heat stress substantially impact plant growth and productivity. When subjected to drought or heat stress, plants exhibit reduction in growth resulting in yield losses. The occurrence of these two stresses together intensifies their negative effects. Unraveling the molecular changes in response to combined abiotic stress is essential to breed climate-resilient crops. In this study, transcriptome profiles were compared between stress-tolerant (Otis), and stress-sensitive (Golden Promise) barley genotypes subjected to drought, heat, and combined heat and drought stress for five days during heading stage. The major differences that emerged from the transcriptome analysis were the overall number of differentially expressed genes was relatively higher in Golden Promise (GP) compared to Otis. The differential expression of more than 900 transcription factors in GP and Otis may aid this transcriptional reprogramming in response to abiotic stress. Secondly, combined heat and water deficit stress results in a unique and massive transcriptomic response that cannot be predicted from individual stress responses. Enrichment analyses of gene ontology terms revealed unique and stress type-specific adjustments of gene expression. Weighted Gene Co-expression Network Analysis identified genes associated with RNA metabolism and Hsp70 chaperone components as hub genes that can be useful for engineering tolerance to multiple abiotic stresses. Comparison of the transcriptomes of unstressed Otis and GP plants identified several genes associated with biosynthesis of antioxidants and osmolytes were higher in the former that maybe providing innate tolerance capabilities to effectively combat hostile conditions. Lines with different repertoire of innate tolerance mechanisms can be effectively leveraged in breeding programs for developing climate-resilient barley varieties with superior end-use traits.

Drought Tolerance Strategies and Autophagy in Resilient Wheat Genotypes

Drought resiliency strategies combine developmental, physiological, cellular, and molecular mechanisms. Here, we compare drought responses in two resilient spring wheat (Triticum aestivum) genotypes: a well-studied drought-resilient Drysdale and a resilient genotype from the US Pacific North-West Hollis. While both genotypes utilize higher water use efficiency through the reduction of stomatal conductance, other mechanisms differ. First, Hollis deploys the drought escape mechanism to a greater extent than Drysdale by accelerating the flowering time and reducing root growth. Second, Drysdale uses physiological mechanisms such as non-photochemical quenching (NPQ) to dissipate the excess of harvested light energy and sustain higher F_v/F_m and ϕ_PSII, whereas Hollis maintains constant NPQ but lower F_v/F_m and ϕ_PSII values. Furthermore, more electron donors of the electron transport chain are in the oxidized state in Hollis than in Drysdale. Third, many ROS homeostasis parameters, including peroxisome abundance, transcription of peroxisome biogenesis genes PEX11 and CAT, catalase protein level, and enzymatic activity, are higher in Hollis than in Drysdale. Fourth, transcription of autophagy flux marker ATG8.4 is upregulated to a greater degree in Hollis than in Drysdale under drought, whereas relative ATG8 protein abundance under drought stress is lower in Hollis than in Drysdale. These data demonstrate the activation of autophagy in both genotypes and a greater autophagic flux in Hollis. In conclusion, wheat varieties utilize different drought tolerance mechanisms. Combining these mechanisms within one genotype offers a promising strategy to advance crop resiliency.

Impact of Wheat Streak Mosaic Virus on Peroxisome Proliferation, Redox Reactions, and Resistance Responses in Wheat

Although peroxisomes play an essential role in viral pathogenesis, and viruses are known to change peroxisome morphology, the role of genotype in the peroxisomal response to viruses remains poorly understood. Here, we analyzed the impact of wheat streak mosaic virus (WSMV) on the peroxisome proliferation in the context of pathogen response, redox homeostasis, and yield in two wheat cultivars, Patras and Pamir, in the field trials. We observed greater virus content and yield losses in Pamir than in Patras. Leaf chlorophyll and protein content measured at the beginning of flowering were also more sensitive to WSMV infection in Pamir. Patras responded to the WSMV infection by transcriptional up-regulation of the peroxisome fission genes PEROXIN 11C (PEX11C), DYNAMIN RELATED PROTEIN 5B (DRP5B), and FISSION1A (FIS1A), greater peroxisome abundance, and activation of pathogenesis-related proteins chitinase, and β-1,3-glucanase. Oppositely, in Pamir, WMSV infection suppressed transcription of peroxisome biogenesis genes and activity of chitinase and β-1,3-glucanase, and did not affect peroxisome abundance. Activity of ROS scavenging enzymes was higher in Patras than in Pamir. Thus, the impact of WMSV on peroxisome proliferation is genotype-specific and peroxisome abundance can be used as a proxy for the magnitude of plant immune response.