Enhancement of drought tolerance in rice by silencing of the OsSYT-5 gene

Investigating how reproductive traits in rice respond to abiotic stress

Rice (Oryza sativa) is one of the most important crops and a food source for billions of people. Anthropogenic global warming, soil erosion, and unstable environmental conditions affect both rice vegetative and reproductive growth, and consequently its final yield. The reproductive phase starts with the transition of the apical meristem from the vegetative to the reproductive phase in which it develops into a panicle and proceeds through the differentiation of the floret and, after fertilization, to the filling of the grain. The physiological events that occur during these stages influence the ability of new seeds to respond to stresses during the future germination phase, a key step for successful seedling growth and future plant establishment. This review explores the impacts of different abiotic stresses on the physiological and molecular pathways of reproductive growth.

Double-truncated version of OsGADs leads to higher GABA accumulation and stronger stress tolerance in Oryza sativa L. var. japonica

KEY MESSAGE

Calmodulin binding domain truncation from OsGAD1 and OsGAD3 resulted in enhanced GABA accumulation, upregulated stress related genes, and improved tolerance to multiple abiotic stresses. Rice (Oryza sativa L.), a critical crop for global food security, faces significant challenges from abiotic stresses. Gamma-aminobutyric acid (GABA), synthesized by glutamate decarboxylase (GAD), plays a vital role in stress tolerance. Truncating the calmodulin-binding domain (CaMBD) in GAD enzymes enhances GAD activity and GABA production. In this study, we developed a hybrid line, Hybrid #78, by crossing two genome-edited lines, OsGAD1ΔC #5 and OsGAD3ΔC #8, with truncated CaMBD in OsGAD1 and OsGAD3, respectively. Hybrid #78 demonstrated significantly improved survival rates in cold (25%), salinity (33%), flooding (83%), and drought (83%) stress conditions, compared with wild-type Nipponbare (0-33%), OsGAD1∆C #5 (0-66%), and OsGAD3∆C #8 (0-50%). Hybrid #78 showed the highest GABA levels during stress, with increases of 3.5-fold (cold), 3.9-fold (salinity), 5-fold (flooding), and 5-fold (drought) relative to wild-type Nipponbare and up to 2-fold higher than that of the parent lines. RNA-seq analysis from shoot tissues in control conditions identified 975 differentially expressed genes between Hybrid #78 and wild-type Nipponbare, with 450 genes uniquely expressed in the hybrid. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment revealed that upregulation in nitrogen metabolism pathways likely contributes to enhanced GABA synthesis via increased glutamate production. Hybrid #78 also showed broader gene expression variability, suggesting enhanced adaptability to stress, especially upregulation of stress-related genes, such as OsDREB, OsHSP70, and OsNAC3. These findings highlight the potential of CaMBD truncation in OsGAD1 and OsGAD3 to develop rice lines with increased GABA accumulation and resilience to multiple abiotic stresses.

Adoption of Multi-omics Approaches to Address Drought Stress Tolerance in Rice and Mitigation Strategies for Sustainable Production

Drought is considered one of the major limiting factors for crop production. Drought-affected areas are consistently expanding. As rice stands as a primary grain widely consumed as a staple food by people across the globe, with a particular prominence in Asian countries. Due to its short root structure, thin cuticular wax layer and quick stomatal closure, rice is considered as drought-sensitive crop. The impact of drought on rice amplifies with plant growth and its adverse effects are more pronounced during the reproductive phase, including stages such as blooming, filling and maturity. Every year rice growers are facing a considerable deterioration of yield due to abiotic stresses specially drought. To address this undesirable consequences, multi-omics approaches are successfully being utilized as a mitigation strategy. A thorough, precise and systematic comprehension of the fundamental biological and cellular mechanisms activated by crop plants during stress is achieved through a range of omics technologies, including genomics, transcriptomics, proteomics and metabolomics. The integration of multi omics approaches offers a holistic understanding of cellular dynamics during drought or other stress conditions. These omics-based tools can identify and manipulate drought-tolerant genes. Utilizing omics approaches to stack these genes in rice contributes to the development of a drought resistant plant architecture. This review article aims to compile the latest published strategies on the application of multi omics approaches to accelerate the development of drought-tolerant rice plants.

Drought's physiological footprint: implications for crop improvement in rice

Rice, a staple food for significant percent of the world's population, is increasingly vulnerable to drought stress, threatening global food security. This review synthesizes current knowledge on drought's physiological impact on rice, highlighting key mechanisms, responses, and adaptations. Drought stress alters rice physiology at various stages, from seed germination to grain filling, affecting yield, quality, and nutrient content. Drought tolerance in rice is influenced by physiological traits such as root architecture and depth, stomatal regulation and water use efficiency, Osmo-protectants and antioxidant defences, hormone signalling and stress response pathways. Genetic diversity and molecular breeding have enhanced drought resilience in rice, with key genes and quantitative trait loci (QTLs) controlling drought tolerance identified, enabling marker-assisted selection and genetic engineering. Despite progress, challenges persist, including limited understanding of drought's impact on rice physiology under field conditions, inefficient screening methods for drought tolerance, and insufficient attention to drought's effects on rice quality and nutritional content. To address these gaps, integrating physiology, genetics, and agronomy for holistic drought mitigation strategies is crucial. Developing high-throughput phenotyping tools for drought tolerance screening and investigating drought's impact on rice grain quality and nutritional content are essential. This review provides a comprehensive framework for understanding drought's physiological footprint in rice and guiding future research toward improving drought tolerance and resilience.

Advances in Understanding Drought Stress Responses in Rice: Molecular Mechanisms of ABA Signaling and Breeding Prospects

Drought stress is a pivotal environmental factor impacting rice production and presents a significant challenge to sustainable agriculture worldwide. This review synthesizes the latest research advancements in the regulatory mechanisms and signaling pathways that rice employs in response to drought stress. It elaborates on the adaptive changes and molecular regulatory mechanisms that occur in rice under drought conditions. The review highlights the perception and initial transmission of drought signals, key downstream signaling networks such as the MAPK and Ca2+ pathways, and their roles in modulating drought responses. Furthermore, the discussion extends to hormonal signaling, especially the crucial role of abscisic acid (ABA) in drought responses, alongside the identification of drought-resistant genes and the application of gene-editing technologies in enhancing rice drought resilience. Through an in-depth analysis of these drought stress regulatory signaling pathways, this review aims to offer valuable insights and guidance for future rice drought resistance breeding and agricultural production initiatives.

Water-saving techniques: physiological responses and regulatory mechanisms of crops

Water-saving irrigation techniques play a crucial role in addressing water scarcity challenges and promoting sustainable agriculture. However, the selection of appropriate water-saving irrigation methods remains a challenge in agricultural production. Additionally, the molecular regulatory mechanisms of crops under water-saving irrigation are not yet clear. This review summarizes the latest research developments in the application of different water-saving irrigation technologies to five important crops (rice, wheat, soybeans, maize, and cotton). It provides an overview of the impact of different irrigation techniques on crop yield, water use efficiency (WUE), physiology, growth, and environmental effects. Additionally, the review compares and contrasts the molecular regulatory mechanisms of crops under water-saving irrigation techniques with those under traditional drought stress, emphasizing the significance of combining irrigation technologies with genetic engineering for developing drought-resistant varieties and improving WUE. Furthermore, the integration of various technologies can stimulate new management strategies, optimize water resource utilization, and enhance sustainability, representing a major focus for future research. In conclusion, this review underscores the importance of water-saving irrigation technologies, especially when combined with genetic engineering, in addressing water resource scarcity, increasing crop yields, and promoting sustainable agriculture.

Transposons are important contributors to gene expression variability under selection in rice populations

Transposable elements (TEs) are an important source of genome variability. Here, we analyze their contribution to gene expression variability in rice by performing a TE insertion polymorphism expression quantitative trait locus mapping using expression data from 208 varieties from the Oryza sativa ssp. indica and O. sativa ssp. japonica subspecies. Our data show that TE insertions are associated with changes of expression of many genes known to be targets of rice domestication and breeding. An important fraction of these insertions were already present in the rice wild ancestors, and have been differentially selected in indica and japonica rice populations. Taken together, our results show that small changes of expression in signal transduction genes induced by TE insertions accompany the domestication and adaptation of rice populations.

Improving abiotic stress tolerance of forage grasses - prospects of using genome editing

Due to an increase in the consumption of food, feed, and fuel and to meet global food security needs for the rapidly growing human population, there is a necessity to obtain high-yielding crops that can adapt to future climate changes. Currently, the main feed source used for ruminant livestock production is forage grasses. In temperate climate zones, perennial grasses grown for feed are widely distributed and tend to suffer under unfavorable environmental conditions. Genome editing has been shown to be an effective tool for the development of abiotic stress-resistant plants. The highly versatile CRISPR-Cas system enables increasingly complex modifications in genomes while maintaining precision and low off-target frequency mutations. In this review, we provide an overview of forage grass species that have been subjected to genome editing. We offer a perspective view on the generation of plants resilient to abiotic stresses. Due to the broad factors contributing to these stresses the review focuses on drought, salt, heat, and cold stresses. The application of new genomic techniques (e.g., CRISPR-Cas) allows addressing several challenges caused by climate change and abiotic stresses for developing forage grass cultivars with improved adaptation to the future climatic conditions. Genome editing will contribute towards developing safe and sustainable food systems.

Transcriptional Comparison of Genes Associated with Photosynthesis, Photorespiration, and Photo-Assimilate Allocation and Metabolic Profiling of Rice Species

The ever-increasing human population alongside environmental deterioration has presented a pressing demand for increased food production per unit area. As a consequence, considerable research effort is currently being expended in assessing approaches to enhance crop yields. One such approach is to harness the allelic variation lost in domestication. This is of particular importance since crop wild relatives often exhibit better tolerance to abiotic stresses. Here, we wanted to address the question as to why wild rice species have decreased grain production despite being characterized by enhanced rates of photosynthesis. In order to do so, we selected ten rice species on the basis of the presence of genome information, life span, the prominence of distribution, and habitat type and evaluated the expression of genes in photosynthesis, photorespiration, sucrose and starch synthesis, sucrose transport, and primary and secondary cell walls. We additionally measured the levels of a range of primary metabolites via gas chromatography–mass spectrometry. The results revealed that the wild rice species exhibited not only higher photosynthesis but also superior CO₂ recovery by photorespiration; showed greater production of photosynthates such as soluble sugars and starch and quick transportation to the sink organs with a possibility of transporting forms such as RFOs, revealing the preferential consumption of soluble sugars to develop both primary and secondary cell walls; and, finally, displayed high glutamine/glutamic acid ratios, indicating that they likely exhibited high N-use efficiency. The findings from the current study thus identify directions for future rice improvement through breeding.