Decoding the wheat awn transcriptome and overexpressing TaRca1β in rice for heat stress tolerance

Identification of Key Genes and Pathways for Anaerobic Germination Tolerance in Rice Using Weighted Gene Co-Expression Network Analysis (WGCNA) in Association with Quantitative Trait Locus (QTL) Mapping

BACKGROUND

Rice is one of the most important food crops in the world, and with the development of direct seeding methods for rice, exposure to anaerobic stress has become a major factor limiting its growth.

RESULTS

In this experiment, we tested the tolerance to anaerobic germination of rice varieties NIP and HD84, and they were used as parents to construct a DH (doubled-haploid) population. The transcriptomes of NIP (highly tolerant) and HD86 (intolerant), and their progeny HR (highly tolerant) and NHR (intolerant) were sequenced from normal and anaerobic environments. The differentially-expressed genes (DEGs) were subjected to GO (Gene ontology), KEGG (Kyoto Encyclopedia of Genes and Genomes), and WGCNA analyses. QTL mapping of the DH population identified tolerance to anaerobic germination-related chromosomal segments. The transcriptome results from 24 samples were combined with the anaerobic stress QTL results for 159 DH population lines to construct a metabolic network to identify key pathways and a gene interaction network to study the key genes. Essential genes were initially subjected to rigorous functional validation, followed by a comprehensive analysis aimed at elucidating their potential utility in domestication and breeding practices, particularly focusing on the exploitation of dominant haplotypes.

CONCLUSION

The results show that pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) are the starting signals of energy metabolism for coleoptile length growth, the auxin transporter EXPA is the determining signal for coleoptile length growth. The pivotal genes Os05g0498700 and Os01g0866100 exert a negative regulatory influence on coleoptile length, ultimately enhancing tolerance to anaerobic germination in rice. Analyses of breeding potential underscore the additional value of Os05g0498700-hyp2 and Os01g0866100-hyp2, highlighting their potential utility in further improving rice through breeding programs. The results of our study will provide a theoretical basis for breeding anaerobic-tolerant rice varieties.

Unveiling differential expression profiles of the wheat DOG1 gene family and functional analysis of the association between TaDOG1-1 and heat stress tolerance in transgenic Arabidopsis

High temperatures can significantly impact wheat growth and grain yields during the grain-filling stage. In this study, we identified genes that respond to high-temperature stress during the grain-filling stage. We also identified and characterized 24 novel genes of the DOG1 gene family in hexaploid wheat. Motif analysis and conserved domain search revealed substantial similarities among TaDOG1 family members. Phylogenetic analysis demonstrated the evolutionary conservation of the TaDOG1 family across various plant species. Tissue-specific expression profiling indicated consistent patterns, with TaDOG1 genes predominantly expressed in stem tissues. Only TaDOG1-1 exhibited enhanced expression, particularly during hard dough and ripening stages. TaDOG1-1 and TaDOG1-7 exhibited increased expression under heat stress during the grain-filling stage, indicating their heat-responsive nature. Cis-element analysis revealed potential regulatory motifs, suggesting the involvement of TaDOG1-1 and TaDOG1-7 in stress tolerance mechanisms. Yeast two-hybrid screening revealed interacting proteins, including stress-responsive and grain development-associated proteins. To understand the biological function, we overexpressed TaDOG1-1 in Arabidopsis plants and observed enhanced thermotolerance under basal heat stress. Under heat stress, the transgenic plants exhibited increased biomass and elevated expression levels of heat-responsive genes. Furthermore, TaDOG1-1-overexpressing plants showed improved survival rates under soil heat stress, along with a greater accumulation of antioxidant enzymes in leaves. In this study, the identification and functions of the DOG1 gene family provide valuable insights for developing genetic engineering strategies aimed at improving wheat yield under high-temperature stress.

Influence mechanism of awns on wheat grain Pb absorption: Awns' significant contribution to grain Pb was mainly originated from their direct absorption of atmospheric Pb at the late grain-filling stage

The spike is the organ that contributes the most to lead (Pb) accumulation in wheat grains. However, as an important photosynthetic and transpiration tissue in spike, the role of awn in wheat grain Pb absorption remains unknown. A field experiment was conducted to investigate the influence mechanism of awn on grain Pb accumulation through two comparative treatments: with and without awns (de-awned treatment). The de-awned treatment decreased wheat yield by 4.1 %; however, it significantly lowered the grain Pb accumulation rate at the late filling stage (15 days after anthesis) and led to a 22.8 % decrease in grain Pb concentration from 0.57 to 0.44 mg·kg^-1. Moreover, the relative contribution of awn-to-grain Pb accumulation gradually increased with the filling process, finally reaching 26.6 % at maturity. In addition, Pb isotope source analysis indicated that the Pb in the awn and grain mainly originated from atmospheric deposition, and the de-awned treatment decreased the proportion of grain Pb from atmospheric deposition by 8.9 %. Microstructural observations further confirmed that the contribution of awns to grain Pb accumulation mainly originated from their direct absorption of atmospheric Pb. In conclusion, awns play an important role in wheat grain Pb absorption at the late grain-filling stage; planting awnless or short-awn wheat varieties may be the simplest and effective environmental management measure to reduce the health risks of Pb in wheat in regions with serious atmospheric Pb contamination.

In vitro application of proline in potato tubers under newly emerging bacteria Lelliottia amnigena infection

Biotic stress deleteriously affects growth, development, and productivity in plants. Proline (Pro) plays a significant role in enhancing plant resistance to pathogen infection. However, its effects on reducing Lelliottia amnigena-induced oxidative stress in potato tubers remain unknown. The present study aims to evaluate the in vitro Pro treatment in potato tubers exposed to a newly emerging bacterium, L. amnigena. Sterilized healthy potato tubers were inoculated with 0.3 mL of L. amnigena suspension (3.69 × 10⁷ CFU mL^-1) 24 h before Pro (5.0 mM) application. The L. amnigena treatment significantly increased the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in the potato tubers by 80.6 and 85.6%, respectively, compared to the control. Application of proline (Pro) decreased MDA and H₂O₂ contents by 53.6 and 55.9%, respectively, compared to the control. Application of Pro to L. amnigena-stressed potato tubers increased the activities of NADPH oxidase (NOX), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), 4-coumaryl-CoA ligase (4CL) and cinnamate-4-hydroxylase (C4H) C4H by 94.2, 96.3, 97.3, 97.1, 96.6, 79.3, 96.4, 93.6, and 96.2%, respectively, compared to the control. In comparison to the control, the genes PAL, SOD, CAT, POD, and NOX were significantly increased in the Pro-treated tubers at 5.0 mM concentration. Tubers treated with Pro + L. amnigena increased the transcript levels of PAL, SOD, CAT, POD, and NOX by 2.3, 2.2, 2.3, 2.5, and 2.8-fold respectively, compared to the control. Our findings suggested that pretreatment of tubers with Pro might reduce lipid peroxidation and oxidative stress by enhancing enzymatic antioxidant activity and gene expression.

Nitric Oxide and Proline Modulate Redox Homeostasis and Photosynthetic Metabolism in Wheat Plants under High Temperature Stress Acclimation

The effects of exogenously-sourced NO (nitric oxide, as 100 µM SNP) and proline (50 mM) in the protection of the photosynthetic performance of wheat (Triticum aestivum L.) plants against heat stress were investigated. The study focused on the mechanisms of proline accumulation, activity, gene expression of antioxidant enzymes, and NO generation. Plants were exposed to a temperature of 40 °C for 6 h per day over 15 days, then allowed to recover at 28 °C. Heat-stressed plants showed increased oxidative stress, with higher levels of H₂O₂ and TBARS (thiobarbituric acid reactive substances) and increased proline accumulation, ACS activity, ethylene evolution, and NO generation, which in turn leads to increased accumulation of antioxidant enzymes and reduced photosynthetic attributes. In the tested wheat cultivar, the exogenous application of SNP and proline under heat stress improved the photosynthesis and reduced oxidative stress by enhancing the enzymatic antioxidant defense system. Potentially, the promoter AOX (alternative oxidase) played a role in maintaining redox homeostasis by lowering H₂O₂ and TBARS levels. The genes for GR antioxidant and photosystem II core protein encoding psbA and psbB were highly up-regulated in nitric oxide and proline treated heat-stressed plants, indicating that ethylene positively impacted photosynthesis under high temperature stress. Moreover, nitric oxide supplementation under high temperature stress optimized ethylene levels to regulate the assimilation and metabolism of proline and the antioxidant system, lowering the adverse effects. The study showed that nitric oxide and proline increased high temperature stress tolerance in wheat by increasing the osmolytes accumulation and the antioxidant system, resulting in enhanced photosynthesis.

'Garlic-lipo'4Plants: Liposome-Encapsulated Garlic Extract Stimulates ABA Pathway and PR Genes in Wheat (Triticum aestivum)

Recently, environmentally friendly crop improvements using next-generation plant biostimulants (PBs) come to the forefront in agriculture, regardless of whether they are used by scientists, farmers, or industries. Various organic and inorganic solutions have been investigated by researchers and producers, focusing on tolerance to abiotic and biotic stresses, crop quality, or nutritional deficiency. Garlic has been considered a universal remedy ever since antiquity. A supercritical carbon dioxide garlic extract encapsulated in nanoscale liposomes composed of plant-derived lipids was examined as a possible PB agent. The present study focused on the characterization of the genes associated with the pathways involved in defense response triggered by the liposome nanoparticles that were loaded with supercritical garlic extracts. This material was applied to Triticum aestivum in greenhouse experiments using foliar spraying. The effects were examined in a large-scale genome-wide transcriptional profiling experiment by collecting the samples four times (0 min, used as a control, and 15 min, 24 h, and 48 h after spraying). Based on a time-course expression analysis, the dynamics of the cellular response were determined by examining differentially expressed genes and applying a cluster analysis. The results suggested an enhanced expression of abscisic acid (ABA) pathway and pathogenesis-related (PR) genes, of which positive regulation was found for the AP2-, C2H2-, HD-ZIP-, and MYB-related transcription factor families.

Improving plant heat tolerance through modification of Rubisco activase in C3 plants to secure crop yield and food security in a future warming world

The world's population may reach 10 billion by 2050, but 10% still suffer from food shortages. At the same time, global warming threatens food security by decreasing crop yields, so it is necessary to develop crops with enhanced resistance to high temperatures in order to secure the food supply. In this review, the role of Rubisco activase as an important factor in plant heat tolerance is summarized, based on the conclusions of recent findings. Rubisco activase is a molecular chaperone determining the activation of Rubisco, whose heat sensitivity causes reductions of photosynthesis at high temperatures. Thus, the thermostability of Rubisco activase is considered to be critical for improving plant heat tolerance. It has been shown that the introduction of thermostable Rubisco activase through gene editing into Arabidopsis thaliana and from heat-adapted wild Oryza species or C4Zea mays into Oryza sativa improves Rubisco activation, photosynthesis, and plant growth at high temperatures. We propose that developing a universal thermostable Rubisco activase could be a promising direction for further studies.

Foliar cytokinins or brassinosteroids applications influence the rice plant acclimatization to combined heat stress

The effect of different foliar sprays numbers of cytokinins - (CK) and brassinosteroids - (BR) on the physiological, biochemical, and panicle parameters of rice plants subjected to combined heat stress (high day/night temperatures) were studied in three different experiments. The treatments established for the first (E1) and second (E2) experiments were the following: i) absolute control, ii) stress control, iii) heat stress + one foliar spray of CK, iv) heat stress + two foliar sprays of CK, v) heat stress + three foliar sprays of CK, vi) heat stress + one foliar spray of BR, vii) heat stress + two foliar sprays of BR, or viii) heat stress + three foliar sprays of BR. For the third experiment (E3), the treatments were the following: i) absolute control, ii) stress control, iii) heat stress + three foliar applications of CK, iv) heat stress + three foliar applications of BR. Rice-stressed plants and sprayed with three foliar sprays of CK or BR had a better stomatal conductance in E1 and E2 compared to their heat-stressed control. The relative tolerance index suggests that three CK or BR applications helped to mitigate the combined heat stress in both experiments. The foliar CK or BR applications at the flowering and grain-filling stages in rice-stressed plants increased Fv/Fm ratio and panicle characteristics (number of filled spikelets and the percentage of panicle blanking in E3). In conclusion, foliar applications of BR or CK can be considered an agronomic strategy to help improve the negative effect of combined heat stress conditions on the physiological behavior of rice plants during different phenological stages.

Overexpression of HVA1 Enhances Drought and Heat Stress Tolerance in Triticum aestivum Doubled Haploid Plants

Plant responses to multiple environmental stresses include various signaling pathways that allow plant acclimation and survival. Amongst different stresses, drought and heat stress severely affect growth and productivity of wheat. HVA1, a member of the group 3 LEA protein, has been well known to provide protection against drought stress. However, its mechanism of action and its role in other stresses such as heat remain unexplored. In this study, doubled haploid (DH) wheat plants overexpressing the HVA1 gene were analyzed and found to be both drought-and heat stress-tolerant. The transcriptome analysis revealed the upregulation of transcription factors such as DREB and HsfA6 under drought and heat stress, respectively, which contribute toward the tolerance mechanism. Particularly under heat stress conditions, the transgenic plants had a lower oxidative load and showed enhanced yield. The overexpression lines were found to be ABA-sensitive, therefore suggesting the role of HsfA6 in providing heat tolerance via the ABA-mediated pathway. Thus, apart from its known involvement in drought stress, this study highlights the potential role of HVA1 in the heat stress signaling pathway. This can further facilitate the engineering of multiple stress tolerance in crop plants, such as wheat.

Physiological and molecular insights on wheat responses to heat stress

Increasing temperature is a key component of global climate change, affecting crop growth and productivity worldwide. Wheat is a major cereal crop grown in various parts of the globe, which is affected severely by heat stress. The morphological parameters affected include germination, seedling establishment, source-sink activity, leaf area, shoot and root growth. The physiological parameters such as photosynthesis, respiration, leaf senescence, water and nutrient relation are also affected by heat. At the cellular level, heat stress leads to the generation of reactive oxygen species that disrupt the membrane system of thylakoid, chloroplast and plasma membrane. The deactivation of the photosystem, reduction in photosynthesis and inactivation of rubisco affect the production of photoassimilates and their allocation. This ultimately affects anthesis, grain filling, size, number and maturity of wheat grains, which hamper crop productivity. The interplay of various systems comprising antioxidants and hormones plays a crucial role in imparting heat stress tolerance in wheat. Thus, implementation of various omics technologies could foster in-depth insights on heat stress effects, eventually devising heat stress mitigation strategies by conventional and modern breeding to develop heat-tolerant wheat varieties. This review provides an integrative view of heat stress responses in wheat and also discusses approaches to develop heat-tolerant wheat varieties.

Unveiling the Actual Functions of Awns in Grasses: From Yield Potential to Quality Traits

Awns, which are either bristles or hair-like outgrowths of lemmas in the florets, are one of the typical morphological characteristics of grass species. These stiff structures contribute to grain dispersal and burial and fend off animal predators. However, their phenotypic and genetic associations with traits deciding potential yield and quality are not fully understood. Awns appear to improve photosynthesis, provide assimilates for grain filling, thus contributing to the final grain yield, especially under temperature- and water-stress conditions. Long awns, however, represent a competing sink with developing kernels for photosynthates, which can reduce grain yield under favorable conditions. In addition, long awns can hamper postharvest handling, storage, and processing activities. Overall, little is known about the elusive role of awns, thus, this review summarizes what is known about the effect of awns on grain yield and biomass yield, grain nutritional value, and forage-quality attributes. The influence of awns on the agronomic performance of grasses seems to be associated with environmental and genetic factors and varies in different stages of plant development. The contribution of awns to yield traits and quality features previously documented in major cereal crops, such as rice, barley, and wheat, emphasizes that awns can be targeted for yield and quality improvement and may advance research aimed at identifying the phenotypic effects of morphological traits in grasses.