Integrated Transcriptomic and Metabolomics Analysis of the Root Responses of Orchardgrass to Submergence Stress

Waterlogging alone and combined with other abiotic stresses provides unique metabolic signatures at the plant-rhizosphere interface: A multi-omics perspective on root metabolome, root exudation and rhizomicrobiome

Despite the growing evidence on unique and unpredictable impact of stress combination over plants, waterlogging-combined stresses effects are still underexplored. Under those conditions, besides the impairment of plant aerial parts, the root system is particularly vulnerable, leading to consequences on plant survival. Here, we report on the short-term exposure of soil-grown Arabidopsis thaliana L. to waterlogging alone and combined with cold, heat, and salinity to inspect their antagonistic, additive or synergistic effects in the rhizosphere. To this aim, root metabolic changes, exudation profiles, and microbial diversity were investigated using a combination of metabolomics and metagenomics, and their interaction was analysed through multi-omics data integration. In roots, waterlogging strongly affected metabolism compared to other single stresses, causing a down-accumulation of targeted classes of compounds including, phenylpropanoids, sterols, terpenoids, and alkaloids. Additive and synergistic effects were reported in roots under waterlogging combined with heat and cold stresses, respectively. Regarding root exudates, flavonoids, terpenoids, and alkaloids were the main classes of compounds affected. Waterlogging caused a down-accumulation of all classes except for coumarins, and mixed trends were observed in waterlogging-combined stresses, with waterlogging-salinity stresses resulting in an ameliorating effect. Even though microbial communities' alpha- and beta-diversity remained stable, suggesting their resilience under short-term exposure, specific taxa modulation was recorded under each condition. Overall, these results contribute to understanding the hierarchical impact of waterlogging on root metabolism and exudation, influencing rhizosphere interactions. This multi-omics approach advances our understanding of plant stress responses and microbial dynamics, paving the way for future studies on adaptive mechanisms.

Effect of AM fungi on the growth and powdery mildew development of Astragalus sinicus L. under water stress

Arbuscular mycorrhizal (AM) fungi are widely existing soil microorganisms that form symbiotic relationships with most terrestrial plants. They are important for enhancing adversity resistance, including resistance to disease and water stresses. Nevertheless, it is not clear whether the benefits can be maintained in regulating the occurrence of plant diseases under drought, flooding stress and during water restoration. In this study, we investigated the effect of AM fungus (Glomus versiforme) on the development of powdery mildew in Chinese milk vetch (Astragalus sinicus) under drought, flooding, and water recovery. The results showed that AM fungal symbiosis promoted the growth of Chinese milk vetch under water stress conditions. It increased the accumulation of ethylene (ET) and jasmonic acid (JA), enhanced the activities of antioxidant enzymes, and decreased the accumulation of salicylic acid (SA) and abscisic acid (ABA). The differentially expressed genes (DEGs) obtained from transcriptome sequencing under each stress were subjected to weighted gene co-expression network analysis (WGCNA), and a total of 12 gene co-expression modules were obtained. The analysis of the relationship between the co-expressed genes in the 12 modules and plant physiological traits showed that the magent, grey60 and darkturquoise modules were significantly associated with ET, SA, JA, ABA, plant defence enzyme activities, malondialdehyde (MDA) and H2O2 content. Water stress and disease were related with the up-regulated expression of genes in the flavonoid biosynthesis and oxidative phosphorylation, plant hormone signal transduction and plant-pathogen interaction pathways. Importantly, inoculation with AM fungus reduced the incidence of powdery mildew under drought stress by 16.54%. In summary, the results of this study showed that inoculation with AM had a positive effect on powdery mildew development tolerance in Chinese milk vetch under drought and flooding stresses and stress recovery. This provides a good basis for field management and sustainable growth of green manure crop Chinese milk vetch.

Physiological and Multi-Omics Integrative Analysis Provides New Insights into Tolerance to Waterlogging Stress in Sesame (Sesamum indicum L.)

Plant growth and development require water, but excessive water hinders growth. Sesame (Sesamum indicum L.) is an important oil crop; it is drought-tolerant but sensitive to waterlogging, and its drought tolerance has been extensively studied. However, the waterlogging tolerance of sesame still has relatively few studies. In this study, two kinds of sesame, R (waterlogging-tolerant) and S (waterlogging-intolerant), were used as materials, and they were treated with waterlogging stress for 0, 24, 72, and 120 h. Physiological analysis showed that after waterlogging, sesame plants responded to stress by increasing the contents of ascorbate peroxidase (APX), glutathione (GSH), and some other antioxidants. The results of the multi-omics analysis of sesame under waterlogging stress revealed 15,652 (R) and 12,156 (S) differentially expressed genes (DEGs), 41 (R) and 47 (S) differentially expressed miRNAs (DEMis), and 896 (R) and 1036 (S) differentially accumulated metabolites (DAMs). The combined DEMi-DEG analysis that 24 DEMis regulated 114 DEGs in response to waterlogging stress. In addition, 13 hub genes and three key pathways of plant hormone signal transduction, glutathione metabolism, and glyoxylate and dicarboxylate metabolism were identified by multi-omics analysis under waterlogging stress. The results showed that sesame regulated the content of hormones and antioxidants and promoted energy conversion in the plant through the above pathways to adapt to waterlogging stress. In summary, this study further analyzed the response mechanism of sesame to waterlogging stress and provides helpful information for the breeding of plants for waterlogging tolerance and genetic improvement.

Accumulation characteristics of plant flavonoids and effects of cultivation measures on their biosynthesis: A review

Flavonoids, a kind of secondary metabolites with both edible, medicinal and antioxidant purposes, could be widely used in food, drug processing, forest products, chemical industry and many other fields. Flavonoid production in plant organs were influenced by numerous internal and external factors at various stages, leading to differential gene expression and transcription factors activity. This study reviews the characteristics of major flavonoids categories, their distribution and accumulation in different plant parts and analyzing their molecular mechanisms. The results showed that: (1) Flavonoids exhibited wide distribution in all parts of the plants, with higher concentrations found in shoots system compared to roots sytem, across most species (predominantly accumulated in leaves and flowers). Plant sex, specific growth and development stages are both impacting indicators; (2) Cultivation methods and abiotic stress could affect plants flavonoid biosynthesis, while inappropriate physical treatments and cultivation methods induced stress in plants, prompting the activation of antioxidant mechanisms for flavonoid synthesis as a defence strategy via indirect pathways; (3) Various key genes and transcription factors collaboratively influenced key enzymes activities and regulate flavonoid biosynthesis, forming a complex regulatory network among these genes and transcription factors; (4) Further studies are required to elucidate whether flavonoid synthesis under various cultivation measures follows direct or indirect pathways. Furthermore, exploring methods for flavonoid biosynthesis and accumulation in specific organs or tissues, as well as identifying plant tissues and microorganisms with high efficiency in flavonoid biosynthesis, is essential for achieving targeted cultivation of plants and quantitative flavonoid production.

Application of multiomics analysis to plant flooding response

Flooding, as a natural disaster, plays a pivotal role in constraining the growth and development of plants. Flooding stress, including submergence and waterlogging, not only induces oxygen, light, and nutrient deprivation, but also alters soil properties through prolonged inundation, further impeding plant growth and development. However, hypoxia (or anoxia) is the most serious and direct damage to plants caused by flooding. Moreover, flooding disrupts the structural integrity of plant cell walls and compromises endoplasmic reticulum functionality, while hindering nutrient absorption and shifting metabolic processes from normal aerobic respiration to anaerobic respiration. It can be asserted that flooding exerts comprehensive effects on plants encompassing phenotypic changes, transcriptional alterations, protein dynamics, and metabolic shifts. To adapt to flooding environments, plants employ corresponding adaptive mechanisms at the phenotypic level while modulating transcriptomic profiles, proteomic characteristics, and metabolite levels. Hence, this study provides a comprehensive analysis of transcriptomic, proteomic, and metabolomics investigations conducted on flooding stress on model plants and major crops, elucidating their response mechanisms from diverse omics perspectives.

Transcriptomic and Metabolomic Analyses Reveal the Response Mechanism of Ophiopogon japonicus to Waterlogging Stress

Ophiopogon japonicus, a plant that thrives in river alluvial dams, often faces waterlogging stress due to sustained rainfall and flood seasons, which significantly impacts its growth and development. Currently, the mechanisms of waterlogging tolerance in Ophiopogon japonicus are still unclear. This study analyzed the transcriptome and metabolome data for Ophiopogon japonicus in the Sichuan region (referred to as CMD) under varying degrees of waterlogging stress: mild, moderate, and severe. The results indicate that the group exposed to flooding stress exhibited a higher number of differentially expressed genes (DEGs) compared to the control group. Notably, most DEGs were downregulated and primarily enriched in phenylpropanoid biosynthesis, starch and sucrose metabolism, and plant hormone signal transduction pathways. A total of 5151 differentially accumulated metabolites (DAMs) were identified, with significantly upregulated DAMs annotated to two clusters, namely flavonoids such as apiin, pelargonin, and others. Furthermore, our study revealed significant upregulation in the expression of C2H2 (C2H2 zinc finger proteins) and AP2/ERF-ERF (the subfamily ERF proteins of APETALA2/ethylene-responsive element binding factors) transcription factors in CMD under flooding stress, suggesting their critical roles in enabling CMD to adapt to these conditions. In conclusion, this research provides insights into the intricate molecular mechanisms underlying CMD's response to flooding stress and reports valuable genetic data for the development of transgenic plants with improved waterlogging tolerance.