Selection of rice breeding lines for resistance to biotic and abiotic stresses.

Rice (Oryza sativa L.) grown in many countries around the world with different climatic conditions and a huge number of environmental stresses, both biotic (fungi, bacteria, viruses, insects) and abiotic (cold, drought, salinity) limit rice productivity. In this regard, breeders and scientists are trying to create rice lines that are resistant to multiple stresses. The aim of this work was to screen and select cold and blast resistant rice breeding lines (RBLs) using molecular markers. Molecular screening of RBLs and parental varieties to cold tolerance was carried out using markers RM24545, RM1377, RM231 and RM569 associated with QTLs (qPSST-3, qPSST-7, qPSST-9). It was discovered that the presence of three QTLs characterizes the cold resistance of studied genotypes, and the absence of one of them leads to cold sensitivity. As a result, 21 cold-resistant out of the 28 studied RBLs were identified. These cold resistant 21 RBLs were further tested to blast resistance using markers Pi-ta, Pita3, Z56592, 195R-1, NMSMPi9-1, TRS26, Pikh MAS, MSM6, 9871.T7E2b, RM224 and RM1233. It was revealed that 16 RBLs from 21 studied lines contain 5-6 blast resistance genes. In accordance with the blast resistance strategy, the presence of 5 or more genes ensures the formation of stable resistance to Magnaporthe oryzae. Thus, 16 lines resistant to multiple stresses, such as cold and blast disease were developed. It should be noted that 6 of these selected lines are high-yielding, which is very important in rice breeding program. These RBLs can be used in breeding process as starting lines, germplasm exchange as a source of resistant genes for the development of new rice varieties resistant to multiple stress factors.

Comprehensive analysis of stress-activated protein kinase genes (OsSAPKs) in rice flowering time.

MAIN CONCLUSION: The rice SnRK2 members SAPK4, SAPK5, SAPK7 and SAPK10 are positive regulators involved in the regulation of rice flowering, while other single mutants exhibited no effect on rice flowering. The rice SnRK2 family, comprising 10 members known as SAPK (SnRK2-Associated Protein Kinase), is pivotal in the abscisic acid (ABA) pathway and crucial for various biological processes, such as drought resistance and salt tolerance. Additionally, these members have been implicated in the regulation of rice heading date, a key trait influencing planting area and yield. In this study, we utilized gene editing technology to create mutants in the Songjing 2 (SJ2) background, enabling a comprehensive analyze the role of each SAPK member in rice flowering. We found that SAPK1, SAPK2, and SAPK3 may not directly participate in the regulatory network of rice heading date, while SAPK4, SAPK5, and SAPK7 play positive roles in rice flowering regulation. Notably, polygene deletion resulted in an additive effect on delaying flowering. Our findings corroborate the previous studies indicating the positive regulatory role of SAPK10 in rice flowering, as evidenced by delayed flowering observed in sapk9/10 double mutants. Moving forward, our future research will focus on analyzing the molecular mechanisms underlying SAPKs involvement in rice flowering regulation, aiming to enhance our understanding of the rice heading date relationship network and lay a theoretical foundation for breeding efforts to alter rice ripening dates.

Systematic identification and characterization of microRNAs with target genes involved in high night temperature stress at the filling stage of rice.

High night temperature stress is one of the main environmental factors affecting rice yield and quality. More and more evidence shows that microRNA (miRNA) plays an important role in various abiotic stresses. However, the molecular network of miRNA regulation on rice tolerance to high night temperatures remains unclear. Here, small RNA, transcriptome and degradome sequencing were integrated to identify differentially expressed miRNAs, genes, and key miRNA-target gene pairs in rice heat-sensitive and heat-tolerant lines at the filling stage suffering from high night temperature stress. It was discovered that there were notable differences in the relative expression of 102 miRNAs between the two rice lines under stress. Meanwhile, 5263 and 5405 mRNAs were differentially expressed in the heat-sensitive line and heat-tolerant line, and functional enrichment analysis revealed that these genes were involved in heat-related processes and pathways. The miRNAs-mRNAs target relationship was further verified by degradome sequencing. Eventually, 49 miRNAs-222 mRNAs target pairs with reverse expression patterns showed significant relative expression changes between the heat-tolerant and the heat-sensitive line, being suggested to be responsible for the heat tolerance difference of these two rice lines. Functional analysis of these 222 mRNA transcripts showed that high night temperature-responsive miRNAs targeted these mRNAs involved in many heat-related biological processes, such as transcription regulation, chloroplast regulation, mitochondrion regulation, protein folding, hormone regulation and redox process. This study identified possible miRNA-mRNA regulation relationships in response to high night temperature stress in rice and potentially contributed to heat resistance breeding of rice in the future.

Comparative miRNome and transcriptome analyses reveal the expression of novel miRNAs in the panicle of rice implicated in sustained agronomic performance under terminal drought stress.

MAIN CONCLUSION: Differential expression of 128 known and 111 novel miRNAs in the panicle of Nagina 22 under terminal drought stress targeting transcription factors, stress-associated genes, etc., enhances drought tolerance and helps sustain agronomic performance under terminal drought stress. Drought tolerance is a complex multigenic trait, wherein the genes are fine-tuned by coding and non-coding components in mitigating deleterious effects. MicroRNA (miRNA) controls gene expression at post-transcriptional level either by cleaving mRNA (transcript) or by suppressing its translation. miRNAs are known to control developmental processes and abiotic stress tolerance in plants. To identify terminal drought-responsive novel miRNA in contrasting rice cultivars, we constructed small RNA (sRNA) libraries from immature panicles of drought-tolerant rice [Nagina 22 (N 22)] and drought-sensitive (IR 64) cultivars grown under control and terminal drought stress. Our analysis of sRNA-seq data resulted in the identification of 169 known and 148 novel miRNAs in the rice cultivars. Among the novel miRNAs, 68 were up-regulated while 43 were down-regulated in the panicle of N 22 under stress. Interestingly, 31 novel miRNAs up-regulated in N 22 were down-regulated in IR 64, whereas 4 miRNAs down-regulated in N 22 were up-regulated in IR 64 under stress. To detect the effects of miRNA on mRNA expression level, transcriptome analysis was performed, while differential expression of miRNAs and their target genes was validated by RT-qPCR. Targets of the differentially expressed miRNAs include transcription factors and stress-associated genes involved in cellular/metabolic/developmental processes, response to abiotic stress, programmed cell death, photosynthesis, panicle/seed development, and grain yield. Differential expression of the miRNAs could be validated in an independent set of the samples. The findings might be useful in genetic improvement of drought-tolerant rice.

Transcriptomic analysis of salt-tolerant and sensitive high-yield japonica rice (Oryza sativa L.) reveals complicated salt-tolerant mechanisms.

Developing and cultivating rice varieties is a potent strategy for reclaiming salinity-affected soils for rice production. Nevertheless, the molecular mechanisms conferring salt tolerance, especially in conventional high-yield japonica rice varieties, remain obscure. In this study, Zhendao 23309 (ZD23309) exhibited significantly less grain yield reduction under a salt stress gradient than the control variety Wuyunjing 30 (WYJ30). High positive correlations between grain yield and dry matter accumulation at the jointing, heading and maturity stages indicated that early salt tolerance performance is a crucial hallmark for yield formation. After a mild salt stress (85 mM NaCl) of young seedlings, RNA sequencing (RNA-seq) of shoot and root separately identified a total of 1952 and 3647 differentially expressed genes (DEGs) in ZD23309, and 2114 and 2711 DEGs in WYJ30, respectively. Gene ontology (GO) analysis revealed numerous DEGs in ZD23309 that play pivotal roles in strengthening salt tolerance, encompassing the response to stimulus (GO:0050896) in shoots and nucleoside binding (GO:0001882) in roots. Additionally, distinct expression patterns were observed in a fraction of genes in the two rice varieties under salt stress, corroborating the efficacy of previously reported salt tolerance genes. Our research not only offers fresh insights into the differences in salt stress tolerance among conventional high-yield rice varieties but also unveils the intricate nature of salt tolerance mechanisms. These findings lay a solid groundwork for deciphering the mechanisms underlying salt tolerance.

The Oryza sativa transcriptome responds spatiotemporally to polystyrene nanoplastic stress.

Nanoplastic represents an emerging abiotic stress facing modern agriculture, impacting global crop production. However, the molecular response of crop plants to this stress remains poorly understood at a spatiotemporal resolution. We therefore used RNA sequencing to profile the transcriptome expressed in rice (Oryza sativa) root and leaf organs at 1, 2, 4, and 8 d post exposure with nanoplastic. We revealed a striking similarity between the rice biomass dynamics in aboveground parts to that in belowground parts during nanoplastic stress, but transcriptome did not. At the global transcriptomic level, a total of 2332 differentially expressed genes were identified, with the majority being spatiotemporal specific, reflecting that nanoplastics predominantly regulate three processes in rice seedlings: (1) down-regulation of chlorophyll biosynthesis, photosynthesis, and starch, sucrose and nitrogen metabolism, (2) activation of defense responses such as brassinosteroid biosynthesis and phenylpropanoid biosynthesis, and (3) modulation of jasmonic acid and cytokinin signaling pathways by transcription factors. Notably, the genes involved in plant-pathogen interaction were shown to be successively modulated by both root and leaf organs, particularly plant disease defense genes (OsWRKY24, OsWRKY53, Os4CL3, OsPAL4, and MPK5), possibly indicating that nanoplastics affect rice growth indirectly through other biota. Finally, we associated biomass phenotypes with the temporal reprogramming of rice transcriptome by weighted gene co-expression network analysis, noting a significantly correlation with photosynthesis, carbon metabolism, and phenylpropanoid biosynthesis that may reflect the mechanisms of biomass reduction. Functional analysis further identified PsbY, MYB, cytochrome P450, and AP2/ERF as hub genes governing these pathways. Overall, our work provides the understanding of molecular mechanisms of rice in response to nanoplastics, which in turn suggests how rice might behave in a nanoplastic pollution scenario.

Measuring Canopy Gas Exchange Using CAnopy Photosynthesis and Transpiration Systems (CAPTS).

Canopy photosynthesis (Ac), rather than leaf photosynthesis, is critical to gaining higher biomass production in the field because the daily or seasonal integrals of Ac correlate with the daily or seasonal integrals of biomass production. The canopy photosynthesis and transpiration measurement system (CAPTS) was developed to enable measurement of canopy photosynthetic CO2 uptake, transpiration, and respiration rates. CAPTS continuously records the CO2 concentration, water vapor concentration, air temperature, air pressure, air relative humidity, and photosynthetic photon flux density (PPFD) inside the chamber, which can be used to derive CO2 and H2O fluxes of a canopy covered by the chamber. This system can also be used to measure the fluxes of greenhouse gases when integrating with CH4 and N2O analyzers. Here, we describe the protocol for using CAPTS to perform experiments on rice (Oryza sativa L.) in paddy field, wheat (Triticum aestivum L.) in upland field, and tobacco (Nicotiana tabacum L.) in pots.

Overexpression of OsNAR2.1 by OsNAR2.1 promoter increases drought resistance by increasing the expression of OsPLDα1 in rice.

BACKGROUND: pOsNAR2.1:OsNAR2.1 expression could significantly increase nitrogen uptake efficiency and grain yield of rice. RESULT: This study reported the effects of overexpression of OsNAR2.1 by OsNAR2.1 promoter on physiological and agronomic traits associated with drought tolerance. In comparison to the wild-type (WT), the pOsNAR2.1:OsNAR2.1 transgenic lines exhibited a significant improvement in survival rate when subjected to drought stress and then irrigation. Under limited water supply conditions, compared with WT, the photosynthesis and water use efficiency (WUE) of transgenic lines were increased by 39.2% and 28.8%, respectively. Finally, the transgenic lines had 25.5% and 66.4% higher grain yield than the WT under full watering and limited water supply conditions, respectively. Compared with the WT, the agronomic nitrogen use efficiency (NUE) of transgenic lines increased by 25.5% and 66.4% under full watering and limited water supply conditions, and the N recovery efficiency of transgenic lines increased by 29.3% and 50.2%, respectively. The interaction between OsNAR2.1 protein and OsPLDα1 protein was verified by yeast hybrids. After drought treatment, PLDα activity on the plasma membrane of the transgenic line increased 85.0% compared with WT. CONCLUSION: These results indicated that pOsNAR2.1:OsNAR2.1 expression could improve the drought resistance of rice by increasing nitrogen uptake and regulating the expression of OsPLDα1.

Physiological dynamics dominate the relationship between solar-induced chlorophyll fluorescence and gross primary productivity along the nitrogen gradient in cropland.

Solar-induced chlorophyll fluorescence (SIF) has been found to be robustly correlated with gross primary productivity (GPP) based on satellite datasets. However, it is unclear whether nitrogen affects the relationship between SIF and GPP at the canopy scale. Here, seasonal dynamics of SIF, GPP, vegetation physiology and canopy structure were measured synchronously throughout growing season along the nitrogen gradient in a rice paddy of China's subtropical region. Our results found that the slope of SIF against GPP was not constant, showing an increasing trend from low to high nitrogen levels. The sensitivity of SIF to nitrogen was larger than that of GPP. Nitrogen enrichment versus deficiency had asymmetrical effects on the SIF-GPP relationship. The steeper slope of SIF against GPP under high nitrogen level was mainly attributed to the promotion of canopy fluorescence efficiency (ΦF) rather than the variation of canopy fluorescence escape probability (Fesc). These results emphasize the vital role of nitrogen in exploring mechanisms underlying SIF dynamics and decoding GPP from SIF.

OsmiR319-OsPCF5 modulate resistance to brown planthopper in rice through association with MYB proteins.

BACKGROUND: The brown planthopper (BPH) is a kind of piercing-sucking insect specific to rice, with the damage tops the list of pathogens and insects in recent years. microRNAs (miRNAs) are pivotal regulators of plant-environment interactions, while the mechanism underlying their function against insects is largely unknown. RESULTS: Here, we confirmed that OsmiR319, an ancient and conserved miRNA, negatively regulated resistance to BPHs, with overexpression of OsmiR319 susceptible to BPH, while suppression of OsmiR319 resistant to BPH in comparison with wild type. Meanwhile, we identified several targets of OsmiR319 that may mediate BPH resistance. Among them, OsPCF5 was the most obviously induced by BPH feeding, and over expression of OsPCF5 was resistance to BPH. In addition, various biochemical assays verified that OsPCF5 interacted with several MYB proteins, such as OsMYB22, OsMYB30, and OsMYB30C.Genetically, we revealed that both OsMYB22 and OsMYB30C positively regulated BPH resistance. Genetic interaction analyses confirmed that OsMYB22 and OsMYB30C both function in the same genetic pathway with OsmiR319b to mediate BPH resistance. CONCLUSIONS: Altogether, we revealed that OsPCF5 regulates BPH resistance via association with several MYB proteins downstream of OsmiR319, these MYB proteins might function as regulators of BPH resistance through regulating the phenylpropane synthesis.

Redundant role of OsCNGC4 and OsCNGC5 encoding cyclic nucleotide-gated channels in rice pollen germination and tube growth.

In staple crops, such as rice (Oryza sativa L.), pollen plays a crucial role in seed production. However, the molecular mechanisms underlying rice pollen germination and tube growth remain underexplored. Notably, we recently uncovered the redundant expression and mutual interaction of two rice genes encoding cyclic nucleotide-gated channels (CNGCs), OsCNGC4 and OsCNGC5, in mature pollen. Building on these findings, the current study focused on clarifying the functional roles of these two genes in pollen germination and tube growth. To overcome functional redundancy, we produced gene-edited rice plants with mutations in both genes using the CRISPR-Cas9 system. The resulting homozygous OsCNGC4 and OsCNGC5 gene-edited mutants (oscngc4/5) exhibited significantly lower pollen germination rates than the wild type (WT), along with severely reduced fertility. Transcriptome analysis of the double oscngc4/5 mutant revealed downregulation of genes related to receptor kinases, transporters, and cell wall metabolism. To identify the direct regulators of OsCNGC4, which form a heterodimer with OsCNGC5, we screened a yeast two-hybrid library containing rice cDNAs from mature anthers. Subsequently, we identified two calmodulin isoforms (CaM1-1 and CaM1-2), NETWORKED 2 A (NET2A), and proline-rich extension-like receptor kinase 13 (PERK13) proteins as interactors of OsCNGC4, suggesting its roles in regulating Ca2+ channel activity and F-actin organization. Overall, our results suggest that OsCNGC4 and OsCNGC5 may play critical roles in pollen germination and elongation by regulating the Ca2+ gradient in growing pollen tubes.

OsRR26, a type-B response regulator, modulates salinity tolerance in rice via phytohormone-mediated ROS accumulation in roots and influencing reproductive development.

MAIN CONCLUSION: OsRR26 is a cytokinin-responsive response regulator that promotes phytohormone-mediated ROS accumulation in rice roots, regulates seedling growth, spikelet fertility, awn development, represses NADPH oxidases, and negatively affects salinity tolerance. Plant two-component systems (TCS) play a pivotal role in phytohormone signaling, stress responses, and circadian rhythm. However, a significant knowledge gap exists regarding TCS in rice. In this study, we utilized a functional genomics approach to elucidate the role of OsRR26, a type-B response regulator in rice. Our results demonstrate that OsRR26 is responsive to cytokinin, ABA, and salinity stress, serving as the ortholog of Arabidopsis ARR11. OsRR26 primarily localizes to the nucleus and plays a crucial role in seedling growth, spikelet fertility, and the suppression of awn development. Exogenous application of cytokinin led to distinct patterns of reactive oxygen species (ROS) accumulation in the roots of both WT and transgenic plants (OsRR26OE and OsRR26KD), indicating the potential involvement of OsRR26 in cytokinin-mediated ROS signaling in roots. The application of exogenous ABA resulted in varied cellular compartmentalization of ROS between the WT and transgenic lines. Stress tolerance assays of these plants revealed that OsRR26 functions as a negative regulator of salinity stress tolerance across different developmental stages in rice. Physiological and biochemical analyses unveiled that the knockdown of OsRR26 enhances salinity tolerance, characterized by improved chlorophyll retention and the accumulation of soluble sugars, K+ content, and amino acids, particularly proline.

Better estimation of evapotranspiration and transpiration using an improved modified Priestly-Taylor model based on a new parameter of leaf senescence in a rice field.

Evapotranspiration (ET) is at the heart of the global water, energy, and carbon cycles. As ET is difficult and expensive to measure, it is crucial to develop estimation models that can be widely applied. Currently, an improved Priestley-Taylor (PT) model considers soil moisture stress, temperature constraints, and leaf senescence; however, its parameter (fs) for simulating crop senescence is based on empirical values, making it difficult to apply to different varieties and complex external conditions and thus challenging to generalize. We improved the parameters fs in the original model based on the chlorophyll decomposition that accompanies crop senescence through easily observable SPAD values (Soil-Plant Analysis Development readings) in the field. We validated the improved model by obtaining ET of different rice varieties in 2022 and 2023 using the energy balance residual method at the Free Air Concentration Enrichment Experimental (FACE) Facility located in Yangzhou City, China. The results showed that the simulation of leaf senescence using SPAD values was feasible and could be extended to different varieties. The new model using improved leaf senescence parameter for estimating ET and transpiration (T) in three plots (2022 and 2023) exhibited slightly enhanced accuracy, particularly at the later stages of crop growth. Moreover, the higher the T/ET ratio of the cropland, the more significant the improvement. This new development enhances the ability of PT models to estimate ET and T using readily available field observations and provides some suggestions for wider application in the field for other crop species.

Mechanisms of chloride to promote the uptake and accumulation of cadmium in rice (Oryza sativa L.).

Cadmium (Cd) contamination in rice ecosystems posed a critical challenge to global food security and environmental health. This study aimed to unveil the key mechanisms trough hydroponic experiments by which chloride (Cl-) promoted the absorption and accumulation of cadmium (Cd) in rice plants. The findings elucidated that the addition of Cl- increased Cd uptake by rice roots (5.1 % âˆ¼ 61 %), acting both directly by enhancing root morphology and indirectly through regulating of the main transporter genes of Cd. The study unveiled that Cl- addition significantly improves Cd bioavailability in roots, which was discernible through the augmentation of Cd concentration and proportion in subcellular fractions, coupled with elevated energy values in key cellular components. Moreover, Cl- addition further augmented the intricate process of Cd transport from roots to shoots (16.1- 86.7 %), which was mainly attributed to the underexpression of OsHMA3 and the decrease in the formation of sulfuhydryl substances. This research provides a comprehensive understanding of the complex mechanisms governing Cd dynamics in rice plants in the presence of Cl-. By elucidating these processes, our findings not only contribute to fundamental knowledge in plant metal uptake but also hold promising implications for mitigating Cd contamination in rice cultivation systems.

Photosynthesis of rice leaves with a parallel venation is highly tolerant to vein severing.

Vein severing in plants caused by leaf damage is common in fields where crops are cultivated. It is hypothesized that leaves with complex reticulate venation can withstand hydraulic disturbances caused by vein severing, thereby preserving leaf carbon assimilation. However, limited research focuses on vein damage of leaves with parallel venation. We studied how vein-severing affected the photosynthetic traits of rice (Oryza sativa) leaves in seconds, minutes and days, under varying water-demand conditions and differing extents of water supply disruption. Rice leaves completely lost their photosynthetic capacity within 2.5 minutes after excision. Severing the midrib resulted in reduced light-saturated photosynthetic rate (A), stomatal conductance (gsw ) and transpiration rate (E) by 2.6, 6.8 and 5.9%, respectively, already after thirty minutes. We further investigated the photosynthetic trait responses to various extents of leaf width severing, while keeping the midrib functional. Surprisingly, A, gsw and E in the downstream area of the severed leaves largely remained stable, showing minimal variation across different leaf width severing ratios. These traits declined only slightly even under increased ambient light intensity and leaf-to-air vapor pressure deficit. This sustained photosynthesis post-severing is attributed to the efficient lateral water transport. Long-term leaf damage slightly but not significantly, impacted the downstream photosynthetic traits within five days post-severing. However, a more pronounced reduction in gas exchange during leaf senescence was observed nine days after severing. These findings suggested that rice leaves can tolerate hydraulic disturbances from vein severing and maintain functionality under various conditions, which is crucial for crop yield stability. However, long-term consequences require further investigation.

A major gene for chilling tolerance variation in Indica rice codes for a kinase OsCTK1 that phosphorylates multiple substrates under cold.

Rice is susceptible to chilling stress. Identifying chilling tolerance genes and their mechanisms are key to improve rice performance. Here, we performed a genome-wide association study to identify regulatory genes for chilling tolerance in rice. One major gene for chilling tolerance variation in Indica rice was identified as a casein kinase gene OsCTK1. Its function and natural variation are investigated at the physiological and molecular level by its mutants and transgenic plants. Potential substrates of OsCTK1 were identified by phosphoproteomic analysis, protein-protein interaction assay, in vitro kinase assay, and mutant characterization. OsCTK1 positively regulates rice chilling tolerance. Three of its putative substrates, acidic ribosomal protein OsP3B, cyclic nucleotide-gated ion channel OsCNGC9, and dual-specific mitogen-activated protein kinase phosphatase OsMKP1, are each involved in chilling tolerance. In addition, a natural OsCTK1 chilling-tolerant (CT) variant exhibited a higher kinase activity and conferred greater chilling tolerance compared with a chilling-sensitive (CS) variant. The CT variant is more prevalent in CT accessions and is distributed more frequently in higher latitude compared with the CS variant. This study thus enables a better understanding of chilling tolerance mechanisms and provides gene variants for genetic improvement of chilling tolerance in rice.

Photoprotective mechanisms and higher photorespiration are key points for iron stress tolerance under heatwaves in rice.

Considering the current climate change scenario, the development of heat-tolerant rice cultivars (Oryza sativa L.) is paramount for cultivation in waterlogged systems affected by iron (Fe) excess. The objective of this work was to investigate the physiological basis of tolerance to excess Fe in rice cultivars that would maintain photosynthetic efficiency at higher temperatures. In an experimental approach, two rice cultivars (IRGA424 - tolerant and IRGA417- susceptible to Fe toxicity) were exposed to two concentrations of FeSO4-EDTA, control (0.019 mM) and excess Fe (7 mM) and subsequent exposition to heatwaves at different temperatures (25 °C - control, 35, 40, 45, 50, and 55 °C). The increase in temperatures resulted in a higher Fe concentration in shoots accompanied by a lower Rubisco carboxylation rate in both cultivars, but with lower damage in the tolerant one. Stomatal limitation only occurred as a late response to Fe toxicity, especially in the sensitive cultivar. The activation of photorespiration as electron sink under Fe excess with increasing temperature during heatwaves appear as a major mechanism to alleviate oxidative stress in cultivars tolerant to excess Fe. The tolerance to iron toxicity and heat stress is associated with increased photoprotective mechanisms driving non-photochemical dissipation.

Impact of individual, combined and sequential stress on photosynthesis machinery in rice (Oryza sativa L).

Abiotic stresses such as heat, drought and submergence are major threats to global food security. Despite simultaneous or sequential occurrence of these stresses being recurrent under field conditions, crop response to such stress combinations is poorly understood. Rice is a staple food crop for the majority of human beings. Exploitation of existing genetic diversity in rice for combined and/or sequential stress is a useful approach for developing climate-resilient cultivars. We phenotyped ~400 rice accessions under high temperature, drought, or submergence and their combinations. A cumulative performance index revealed Lomello as the best performer across stress and stress combinations at the seedling stage. Lomello showed a remarkable ability to maintain a higher quantum yield of photosystem (PS) II photochemistry. Moreover, the structural integrity of the photosystems, electron flow through both PSI and PSII and the ability to protect photosystems against photoinhibition were identified as the key traits of Lomello across the stress environments. A higher membrane stability and an increased amount of leaf chlorophyll under stress may be due to an efficient management of reactive oxygen species (ROS) at the cellular level. Further, an efficient electron flow through the photosystems and, thus, a higher photosynthetic rate in Lomello is expected to act as a sink for ROS by reducing the rate of electron transport to the high amount of molecular oxygen present in the chloroplast. However, further studies are needed to identify the molecular mechanism(s) involved in the stability of photosynthetic machinery and stress management in Lomello during stress conditions.

OsGEX3 affects anther development and improves osmotic stress tolerance in rice.

MAIN CONCLUSION: Overexpression and loss of function of OsGEX3 reduce seed setting rates and affect pollen fertility in rice. OsGEX3 positively regulates osmotic stress response by regulating ROS scavenging. GEX3 proteins are conserved in plants. AtGEX3 encodes a plasma membrane protein that plays a crucial role in pollen tube guidance. However, the function of its homolog in rice, OsGEX3, has not been determined. Our results demonstrate that OsGEX3 is localized in the plasma membrane and the nucleus as shown by a transiently transformed assay using Nicotiana benthamiana leaves. The up-regulation of OsGEX3 was detected in response to treatments with polyethylene glycol (PEG) 4000, hydrogen peroxide, and abscisic acid (ABA) via RT-qPCR analysis. Interestingly, we observed a significant decline in the seed setting rates of OsGEX3-OE lines and mutants, compared to the wild type. Further investigations reveal that overexpression and loss of function of OsGEX3 affect pollen maturation. TEM observation revealed a significant decrease in the fertile pollen rates of OsGEX3-OE transgenic lines and Osgex3 mutants due to a delay in pollen development at the late vacuolated stage. Overexpression of OsGEX3 improved osmotic stress and oxidative stress tolerance by enhancing reactive oxygen species (ROS) scavenging in rice seedlings, whereas Osgex3 mutants exhibited an opposite phenotype in osmotic stress. These findings highlight the multifunctional roles of OsGEX3 in pollen development and the response to abiotic stress. The functional characterization of OsGEX3 provides a fundamental basis for rice molecular breeding and can facilitate efforts to cultivate drought resistance and yield-related varieties.

Histone deacetylase OsHDA716 represses rice chilling tolerance by deacetylating OsbZIP46 to reduce its transactivation function and protein stability.

Low temperature is a major environmental factor limiting plant growth and crop production. Epigenetic regulation of gene expression is important for plant adaptation to environmental changes, whereas the epigenetic mechanism of cold signaling in rice (Oryza sativa) remains largely elusive. Here, we report that the histone deacetylase (HDAC) OsHDA716 represses rice cold tolerance by interacting with and deacetylating the transcription factor OsbZIP46. The loss-of-function mutants of OsHDA716 exhibit enhanced chilling tolerance, compared with the wild-type plants, while OsHDA716 overexpression plants show chilling hypersensitivity. On the contrary, OsbZIP46 confers chilling tolerance in rice through transcriptionally activating OsDREB1A and COLD1 to regulate cold-induced calcium influx and cytoplasmic calcium elevation. Mechanistic investigation showed that OsHDA716-mediated OsbZIP46 deacetylation in the DNA-binding domain reduces the DNA-binding ability and transcriptional activity as well as decreasing OsbZIP46 protein stability. Genetic evidence indicated that OsbZIP46 deacetylation mediated by OsHDA716 reduces rice chilling tolerance. Collectively, these findings reveal that the functional interplay between the chromatin regulator and transcription factor fine-tunes the cold response in plant and uncover a mechanism by which HDACs repress gene transcription through deacetylating nonhistone proteins and regulating their biochemical functions.