Redox metabolic and molecular parameters for screening drought tolerant indigenous aromatic rice cultivars

Comparative transcriptomic data confirm the findings of dehydration stress-induced redox biology of indigenous aromatic rice cultivars

The present work compares the transcriptome data sets of post-imbibitional dehydration stress-raised seedlings of two contrasting indigenous aromatic rice cultivars (Oryza sativa L., Cultivars Jamainadu and Badshabhog) for unfolding genetic regulation of dehydration stress. The result of RNA-seq analysis in Illumina platform in general revealed significant cultivar-specific expression of genes under dehydration stress that substantiate the data of redox metabolic fingerprints (assessed in terms of differential efficacy of ascorbate-glutathione pathway, ROS-antioxidant interaction dynamics and sensitive biomarkers of oxidative stress). Both the cultivars showed a diverse global transcriptomic response under water-deficit condition. Transcripts selected for heatmap generation with proper annotation revealed genes that are significantly expressed and mainly involved in redox functions, signaling, membrane trafficking, replication, protein synthesis, etc. Gene ontology (GO) analysis proposed that dehydration stress in the drought-tolerant cultivar Badshabhog was attributable to the enhanced expression of genes associated with carbon dioxide-concentrating mechanism, peroxysomal biogenesis, protein modification, protein synthesis, mitochondrial electron transport chain functioning, intercellular protein transport, histone demethylation associated with developmental process, regulation of apoptosis, etc. The redox genes that got significantly over-expressed in the IARC Badshabhog vis-à-vis Jamainadu include l-ascorbate oxidase/peroxidase, monothiol glutaredoxin-S1, thioredoxin-like protein AAED1 (chloroplastic), thioredoxin-like protein CXXS1, NADH-dehydrogenase (ubiquinone)-1-beta subcomplex subunit 3-B, NADH-dehydrogenase subunit 6 and K, lipoxygenase 6 isoform-XI, etc. Overall, the results of the RNA-seq analysis led to the identification of cultivar-specific genes, with the cultivar Badshabhog exhibiting significantly greater molecular reprogramming for redox regulation and signaling necessary for combating dehydration stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03829-z.

Herbal and chemical seed potentiations improve the redox health of aged seeds of indigenous aromatic rice cultivars through regulation of oxidative window, gene expression, and restoration of hormonal homeostasis

Previous studies associated with seed potentiation support the critical role of metabolic readjustment in restricting the loss of seed vigor and viability of aged seeds. However, their exact role in the regulation of 'oxidative windows' of potentiated seeds is rarely studied and hence is the subject of the present investigation. Seed potentiation of two contrasting indigenous aromatic rice cultivars, differing in sensitivity towards redox attributes (Oryza sativa L., Cultivars Tulaipanji and Jamainadu), with standardized doses of hydrogen peroxide (20 mM), triadimefon (250 μM), herbal extract (1% aqueous extract of Lantana camara flower) and distilled water before accelerated aging (RH 92% and 41 °C for 24 h) found to have significant impact on redox regulation of aged seeds and improvement of germination phenotypes. The efficacy of integrated RBOH-ascorbate-glutathione/catalase pathway, redox status and other redox fingerprints in the metabolic landscape of potentiated-aged seeds vis-a-vis non-potentiated-aged seeds corroborate the impact of seed potentiation on the regulation of 'oxidative window' of experimental rice seeds. Gene expression analysis of central redox hub enzymes (Osrboh, OsAPx2, OsGRase, OsCatA) strongly substantiates the impact of seed potentiation on transcriptional regulation of genes for redox homeostasis in accelerated aged seeds. The novelty of the current effort is that it suggests a positive nexus between seed potentiation-induced redox regulation and hormonal homeostasis. The efficacy of seed potentiation on the redox regulation of experimental accelerated aged seeds is found to be cultivar-specific and comparatively better in the cultivar Tulaipanji as compared to the cultivar Jamainadu and in the order herbal extract, hydrogen peroxide, hydropriming and triadimefon.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01375-9.

Drought stress in rice: morpho-physiological and molecular responses and marker-assisted breeding

Rice (Oryza Sativa L.) is an essential constituent of the global food chain. Drought stress significantly diminished its productivity and threatened global food security. This review concisely discussed how drought stress negatively influenced the rice's optimal growth cycle and altered its morpho-physiological, biochemical, and molecular responses. To withstand adverse drought conditions, plants activate their inherent drought resistance mechanism (escape, avoidance, tolerance, and recovery). Drought acclimation response is characterized by many notable responses, including redox homeostasis, osmotic modifications, balanced water relations, and restored metabolic activity. Drought tolerance is a complicated phenomenon, and conventional breeding strategies have only shown limited success. The application of molecular markers is a pragmatic technique to accelerate the ongoing breeding process, known as marker-assisted breeding. This review study compiled information about quantitative trait loci (QTLs) and genes associated with agronomic yield-related traits (grain size, grain yield, harvest index, etc.) under drought stress. It emphasized the significance of modern breeding techniques and marker-assisted selection (MAS) tools for introgressing the known QTLs/genes into elite rice lines to develop drought-tolerant rice varieties. Hence, this study will provide a solid foundation for understanding the complex phenomenon of drought stress and its utilization in future crop development programs. Though modern genetic markers are expensive, future crop development programs combined with conventional and MAS tools will help the breeders produce high-yielding and drought-tolerant rice varieties.

Exploring the parameters of central redox hub for screening salinity tolerant rice landraces of coastal Bangladesh

Regulation of oxidative stress towards origin of favorable internal redox cue plays a decisive role in salinity stress acclimation and least studied in rice and hence is the subject of present investigation. Redox landscaping of seedlings of ten experimental land races of rice of coastal Bangladesh grown under post imbibitional salinity stress (PISS) has been done through characterization of ROS-antioxidant interaction dynamics at metabolic interface, transcriptional reprogramming of redox-regulatory genes along with the assessment of biomarkers of oxidative threat for standardizing redox strategies and quality parameters for screening. The results exhibited a strong correlation between salinity induced redox status (pro-oxidant/antioxidant ratio, efficacy of H₂O₂ turnover through integrated RboH-Ascorbate–Glutathione/Catalase pathway and estimation of sensitive redox biomarkers of oxidative deterioration) and germination phenotypes of all landraces of rice. Transcript abundance of the marker genes of the enzymes associated with central antioxidant hub for H₂O₂ processing (CatA, OsAPx2, SodCc2, GRase and RboH) of all experimental landraces of the rice advocate the central role of H₂O₂ turnover dynamics in regulating redox status and salinity tolerance. Landraces suffering greater loss of abilities of decisive regulation of H₂O₂ turnover dynamics exhibited threat on the oxidative windows of the germinating seeds under salinity.

Comparative Physiology of Indica and Japonica Rice under Salinity and Drought Stress: An Intrinsic Study on Osmotic Adjustment, Oxidative Stress, Antioxidant Defense and Methylglyoxal Detoxification

Salinity and drought stress are significant environmental threats, alone or in combination. The current study was conducted to investigate the morpho-physiology, osmotic adjustment, oxidative stress, antioxidant defense and methylglyoxal detoxification of three rice genotypes from the indica (cv. BRRI dhan29 and BRRI dhan48) and japonica (cv. Koshihikari) groups. Eighteen-day-old seedlings of these genotypes were exposed to either in alone salinity (150 mM NaCl) and drought (15% PEG 6000) or in the combination of salinity and drought (150 mM NaCl + 15% PEG 6000) stress in vitro for 72 h. Compared with the control, the water status, biomass and photosynthetic pigments were decreased, where a significant increase was seen in the mortality rate, hydrogen peroxide content, electrolyte leakage, lipoxygenase activity, level of malondialdehyde and methylglyoxal, indicating increased lipid peroxidation in rice genotypes in stress conditions. The non-enzymatic and enzymatic components of the ascorbate-glutathione (AsA-GSH) pool in rice genotypes were disrupted under all stress treatments, resulting imbalance in the redox equilibrium. In contrast, compared to other rice genotypes, BRRI dhan48 revealed a lower Na+/K+ ratio, greater proline (Pro) levels, higher activity of AsA, dehydroascorbate (DHA) and GSH, lower glutathione disulfide (GSSG) and a higher ratio of AsA/DHA and GSH/GSSG, whereas enzymatic components increased monodehydroascorbate reductase, dehydroascorbate reductase, glutathione peroxidase and glyoxalase enzymes. The results showed that a stronger tolerate ability for BRRI dhan48 against stress has been connected to a lower Na+/K+ ratio, an increase in Pro content and an improved performance of the glyoxalase system and antioxidant protection for scavenging of reactive oxygen species. These data can give insight into probable responses to single or combination salinity and drought stress in rice genotypes.

Complementation of ROS scavenging secondary metabolites with enzymatic antioxidant defense system augments redox-regulation property under salinity stress in rice

The RP-HPLC based comparative quantification of some important redox sensitive phenolic acids and flavonoids revealed overall greater elicitation of chalcone synthase related flavonoid biosynthetic pathway, concomitant with the greater utilization of cinnamic acid for the seedlings of the salinity resistant rice cultivar Patnai as compared to susceptible cultivar IR29 grown under post imbibitional salinity stress (PISS). When compared, the cultivar Patnai further exhibited significantly better antioxidant-coupled redox-regulation by up regulating ascorbate-glutathione pathway and reducing the expression of oxidative deterioration under PISS as compared to its counterpart, the cultivar IR29. A model for redox homeostasis in which complementation of action of ROS scavenging secondary metabolites with enzymatic antioxidant defense at metabolic interface necessary for maintenance of the redox homeostasis to combat salinity stress has been proposed.

Harnessing leaf photosynthetic traits and antioxidant defence for multiple stress tolerance in three premium indigenous rice landraces of Jeypore tract of Odisha, India

The aim of the present research was to compare the effects of different abiotic stresses (drought, salinity and submergence) on growth, photosynthesis and PSII activity along with antioxidant defence of three premium rice landraces, namely Kalajeera, Machhakanta and Haladichudi from Jeypore tract of Odisha, India to evaluate their performance under multiple stresses and possibility of using in the pre-breeding programs. Results showed that drought, salinity and submergence significantly reduced plant growth, leaf photosynthesis, water use efficiency (WUE), carboxylation efficiency (CE), PSII activity and SPAD chlorophyll index, and the highest effect was observed in susceptible check variety (IR64). In addition, the indigenous rice lines showed better stomatal traits such as stomatal density (SD), stomatal size (SS) and stomatal number per leaf area (S/LA). Notably, higher activities of antioxidative enzymes and proline accumulation was observed in studied indigenous rice landraces and were found comparable with the drought and salinity tolerant (N22) and submergence tolerant (FR13A) check varieties. Based on our findings it was revealed that these landraces can be expected to possess an adequate level of tolerance to drought, salinity and submergence and showed adaptive fitness to multiple stresses during seedling stage. These landraces can be considered as potential donor for future rice pre-breeding program.

Physiological characterization and allelic diversity of selected drought tolerant traditional rice (Oryza sativa L.) landraces of Koraput, India

Water-deficit stress tolerance in rice is important for maintaining stable yield, especially under rain-fed ecosystem. After a thorough drought-tolerance screening of more than 130 rice genotypes from various regions of Koraput in our previous study, six rice landraces were selected for drought tolerance capacity. These six rice landraces were further used for detailed physiological and molecular assessment under control and simulated drought stress conditions. After imposing various levels of drought stress, leaf photosynthetic rate (P_N), photochemical efficiency of photosystem II (Fv/Fm), SPAD chlorophyll index, membrane stability index and relative water content were found comparable with the drought-tolerant check variety (N22). Compared to the drought-susceptible variety IR64, significant positive attributes and varietal differences were observed for all the above physiological parameters in drought-tolerant landraces. Genetic diversity among the studied rice landraces was assessed using 19 previously reported drought tolerance trait linked SSR markers. A total of 50 alleles with an average of 2.6 per locus were detected at the loci of the 19 markers across studied rice genotypes. The Nei's genetic diversity (He) and the polymorphism information content (PIC) ranged from 0.0 to 0.767 and 0.0 to 0.718, respectively. Seven SSR loci, such as RM324, RM19367, RM72, RM246, RM3549, RM566 and RM515, showed the highest PIC values and are thus, useful in assessing the genetic diversity of studied rice lines for drought tolerance. Based on the result, two rice landraces (Pandkagura and Mugudi) showed the highest similarity index with tolerant check variety. However, three rice landraces (Kalajeera, Machhakanta and Haldichudi) are more diverse and showed highest genetic distance with N22. These landraces can be considered as the potential genetic resources for drought breeding program.