Pre-harvest sprouting (PHS), defined as the premature germination of grains on the panicle before harvest, significantly compromises grain yield and seed quality. Optimizing seed dormancy is therefore crucial for mitigating PHS. Here, we report that loss of function in Stress-associated Protein 5 (OsSAP5) enhances resistance to PHS without grain yield reduction. Mechanistically, OsSAP5 participates in the GA-mediated modulation of the DELLA protein OsSLR1 abundance to orchestrate downstream responses; it accelerates GA signaling transduction to induce amylase gene expression and elevate soluble sugar content, while concurrently suppressing the expression of ABA signaling regulators, thereby collaboratively governing seed dormancy and germination. In ossap5 mutants, this bipartite control-manifested as intensified dormancy alongside delayed germination-acts in concert to repress PHS. We further confirm an interaction between OsSAP5 and OsSLR1, which likely plays a role in this regulatory process. Correspondingly, we also established that OsSLR1 positively regulates seed dormancy and negatively regulates seed germination, thereby further elaborating its biological functions. In conclusion, our findings identify OsSAP5 as a pivotal modulator of GA signaling, offering a new theoretical basis and genetic target for breeding PHS-resistant varieties.

Seed dormancy is a complex developmental and agronomic trait requiring a delicate balance: insufficient dormancy leads to pre-harvest sprouting (PHS), while excessive dormancy causes uneven germination. Understanding the intrinsic mechanisms resolving this trade-off is vital for crop improvement. In this study, our findings indicate that the heat shock transcription factor OsHsfA2a acts as a negative regulator of seed dormancy. The hsfa2a knockout mutants exhibited enhanced PHS resistance while maintaining yield potential and post-harvest germination rates, offering a potential strategy to uncouple PHS resistance from agronomic penalties. Mechanistically, our data suggest that OsHsfA2a self-associates and can activate the ABA catabolic gene OsABA8ox3, thereby promoting dormancy release. Furthermore, genetic analysis using the sd6 hsfa2a double mutant supports the hypothesis that the bHLH transcription factor OsSD6 is epistatic to OsHsfA2a, acting as an upstream initiator. Biochemically, OsSD6 transcriptionally activates OsHsfA2a. Once expressed, OsHsfA2a likely amplifies the signal via a self-activation loop. However, the accumulating OsSD6 protein physically interacts with OsHsfA2a, which we propose competitively attenuates its DNA-binding capacity. These results support a multi-tiered regulatory module operating across both transcriptional and post-translational levels. Collectively, our findings provide insights into an intrinsic physiological mechanism by which this module fine-tunes ABA catabolism to govern primary seed dormancy, providing precise genetic targets for mitigating PHS.

Stress-associated proteins (SAPs), a class of zinc-finger proteins, play crucial roles in plant responses to abiotic stresses, including high temperature; however, their underlying mechanism is largely unknown. Here, we report that a heat-induced E3 ubiquitin ligase OsSAP3 negatively regulates thermotolerance in rice (Oryza sativa) by specifically interacting with the small heat shock protein OsHSP16. Knockout of OsSAP3 improves seedling survival and maintains grain-setting rates under heat stress. OsSAP3 ubiquitinates the lysine residues K128 and K145 in OsHSP16 to regulate its stability. Unlike OsSAP3, OsHSP16 functions as a positive regulator of thermotolerance in rice, and this enhanced heat resistance correlates with increased antioxidant enzyme activity, reduced reactive oxygen species (ROS) accumulation, decreased relative electrolyte leakage, and upregulation of heat stress defense genes. Genetic interaction analysis supports that OsSAP3 and OsHSP16 operate in the same pathway to modulate heat stress responses, albeit with opposing roles. Furthermore, OsHSP16 binds to and promotes the degradation of putatively misfolded or damaged OsAPX2 (ascorbate peroxidase 2) proteins, which may contribute to its role in enhancing thermotolerance in rice. Collectively, our findings reveal a key molecular framework controlling rice heat tolerance and provide a potential gene-editing-based strategy to enhance crop heat resilience.

Seed vigor is a critical agronomic trait in rice (Oryza sativa L.) cultivation, determining rapid and uniform germination and seedling establishment. Although numerous auxin response factors (OsARFs) regulate various important traits in rice, their functions regarding seed vigor remain unclear. Here, we demonstrate that OsARF22 functions as a predominant positive regulator of seed vigor. Loss of OsARF22 resulted in reduced seed germination and impaired seedling establishment, whereas overexpression of OsARF22 enhanced seed vigor. OsARF10, a homolog of OsARF22, played a partially redundant but minor role. Transcriptomic analysis revealed that OsABI5 is preferentially associated with OsARF22, and that the OsARF22-OsABI5 module co-regulates a set of ABA-responsive genes. Mechanistically, OsARF22 directly interacts with OsABI5 and promotes its proteasomal degradation, thereby suppressing ABA signaling. In Osarf22 mutants, impaired OsABI5 degradation, together with ABA accumulation and enhanced OsABI5 transcription, leads to OsABI5 hyperaccumulation and suppression of seed vigor. Our findings uncover a regulatory module in which OsARF22 acts as a post-translational repressor of ABA signaling to promote seed vigor, and highlight OsARF22 as a potential target for breeding rice varieties with high seed vigor. This work provides insights into the functional diversification of orthologous transcription factors across species.

High seed vigor is an important trait for successful seed germination and seedling establishment in rice. However, the underlying regulatory mechanism remains unclear. In this study, we identified the stress associated protein gene OsSAP3 as a key regulator of seed vigor. Quantitative reverse transcription PCR (qRT-PCR) analysis revealed that OsSAP3 is highly expressed during seed development and germination, with its expression further induced by abscisic acid (ABA) during germination. Knockout of OsSAP3 resulted in reduced reserve mobilization capacity during rice seed germination, elevated expression levels of ABA signaling transduction genes, and enhanced sensitivity to ABA, ultimately leading to decreased seed vigor. Meanwhile, Ossap3 seeds narrowed the appropriate germination temperature range, which is due to their lower endogenous hydrogen peroxide (H2O2) levels. Exogenous H2O2 treatment could restore the seed vigor of Ossap3 by accelerating ABA degradation, suppressing ABA signaling, and enhancing starch mobilization via α-amylase-mediated hydrolysis to increase soluble metabolites. These regulatory mechanisms mediated by OsSAP3 are crucial for enhancing rice seed vigor and broadening temperature adaptability during seed germination, providing critical insights into the molecular mechanisms underlying seed vigor regulation.

Heading date, a critical agronomic trait determining rice regional adaptation and yield potential, is regulated by complex genetic networks. Although stress-associated proteins (SAPs) are well-documented mediators of abiotic stress responses, their roles in reproductive development remain poorly characterized. Here we demonstrate that stress-associated protein 5 (OsSAP5) functions as a positive regulator of heading date in rice. Loss-of-function ossap5 mutants exhibited significant heading delay under natural short day condition, accompanied by marked downregulation of florigen genes Hd3a and RFT1 and subsequent suppression of MADS-box genes in the shoot apical meristem (SAM). A similar decrease in expression of florigen genes was observed in OsGF14c overexpression lines under short day condition. The molecular and biochemical assays confirmed that OsSAP5 interacts with OsGF14c. Notably, OsSAP5 had E3 ubiquitin ligase activity and might promote the ubiquitination of OsGF14c. Therefore, OsSAP5 regulates heading date by interacting with OsGF14c under short day condition.

Cold and hypoxia (CH) stress, a common combined stress during floating system, inhibits growth of tobacco and seriously affects the quality. Exogenous substances can regulate plant growth and respond to environmental stress. However, there are few studies focusing on tobacco responses to CH stress and the effects of exogenous substances on tobacco seedlings under CH stress are not fully understood. In this study, metabolomics analysis was performed on two tobacco varieties with contrasting CH responses, i.e. K326 (CH-sensitive) and Honghua (CH-tolerant). The results showed that flavonoids were crucial for tobacco seedlings to resist CH stress. Furthermore, exogenous anthocyanidin, flavone and quercetin significantly increased the root length, relative chlorophyll content, SP content, SOD, POD, CAT and APX activities of tobacco under CH stress, while reducing MDA content. Overall, our study highlighted the potential of flavonoids to improve CH tolerance of tobacco which could become a useful tool to resist stress during tobacco floating system.

In the original publication [...].

The small heat shock protein OsHsp20-25, from long-lived mRNA, negatively regulates seed germination but positively regulates seed length. The mRNAs stored for a longer period in mature and dry seeds are called long-lived mRNA, which encodes diverse protein families and plays important roles in seed vigor. However, the specific contributions of individual mRNA populations to germination regulation remain poorly defined. In this study, we analyzed four small heat shock proteins, OsHsp20-17, OsHsp20-18, OsHsp20-20, and OsHsp20-25, from RNA sequencing data of rice seed. They were specifically expressed in the late stage of seed development and early stage of seed germination. Intriguingly, their transcripts retained detectable expression levels in one-year-old stored seeds. Four transgenic lines of OsHsp20s were generated, and only the OsHsp20-25 overexpression lines exhibited lower germination rates compared to the wild-type, accompanied by upregulated expression of OsABI5 and OsMFT2, and enhanced ABA sensitivity. Furthermore, OsHsp20-25-CRISPR mutants produced seeds of shorter length, but the overexpression line showed longer seeds. Biochemical and molecular evidence demonstrates that OsHsp20-25 interacted with OsHsp20-18, which also interacted with an F-box domain protein OsFBL45 in vivo and in vitro. Overall, OsHsp20, as a long-lived mRNA, plays important roles in seed development and seed germination.

Tobacco is one of the important cash crops in China. It is sensitive to low temperature, especially in the early stage of tobacco seed germination and seedling growth. Low temperature stress directly affects the germination of tobacco seeds, leading to irregular emergence and slow growth of seedlings. Therefore, it is important to improve the vigor and cold tolerance of tobacco. In this study, two cold-sensitive tobacco varieties were primed individually with ZnSO4, FeSO4 and Na2SeO3 to test the effects of different microelements priming on seed germination. The results showed that under low temperature (11 degrees C), all three elements could improve tobacco seed vigor and promote seed germination, with selenium priming exhibiting the best effect. Selenium priming significantly increased the seed vigor index of YY97 by 29.60 % and of YY85 by 47.57 %. Moreover, selenium priming could effectively enhance POD activity in seeds, promote the oxidation of phenolic substances and enhance the activities of G-6-PDH and 6-P-GDH in the process of scavenging ROS and converting H2O2 to center dot O-2(-). The results suggested that selenium played an important role in promoting tobacco seed germination under low temperature.

The pollen viability directly affects the pollination process and the ultimate grain yield of rice. Here, we identified that the MORN motif-containing proteins, OsMORN1 and OsMORN2, had a crucial role in maintaining pollen fertility. Compared with the wild type (WT), the pollen viability of the osmorn1 and osmorn2 mutants was reduced, and pollen germination was abnormal, resulting in significantly lower spikelet fertility, seed-setting rate, and grain yield per plant. Further investigation revealed that OsMORN1 was localized to the Golgi apparatus and lipid droplets. Lipids associated with pollen viability underwent alterations in osmorn mutants, such as the diacylglyceride (18:3_18:3) was 5.1-fold higher and digalactosyldiacylglycerol (18:2_18:2) was 5.2-fold lower in osmorn1, while the triacylglycerol (TG) (16:0_18:2_18:3) was 8.3-fold higher and TG (16:0_18:1_18:3) was 8.5-fold lower in osmorn2 than those in WT. Furthermore, the OsMORN1/2 was found to be associated with rice cold tolerance, as osmorn1 and osmorn2 mutants were more sensitive to chilling stress than WT. The mutants displayed increased hydrogen peroxide accumulation, reduced antioxidant enzyme activities, elevated malondialdehyde content, and a significantly decreased seedling survival rate. Lipidomics analysis revealed distinct alterations in lipids under low temperature, highlighting significant changes in TG (18:2_18:3_18:3) and TG (18:4_18:2_18:2) in osmorn1, TG (16:0_18:2_18:2) and PI (17:2_18:3) in osmorn2 compared to the WT. Therefore, it suggested that OsMORN1 and OsMORN2 regulate both pollen viability and cold tolerance through maintaining lipid homeostasis.

Yield potential, plant height and flowering time are three classes of traits that determine the productivity of rice. Rice heading greatly depends on the accurate measurement of environment changes, particularly in day length and temperature. We discuss all genes reported to be related to the heading time in this review. The accumulation of florigen, such as Hd3a or RFT1, is the key factor for rice heading. Florigen is found in the rice leaf and then transports into the shoot apical meristem (SAM), where floral initiation occurs. We discuss the formation of florigen activation complex (FAC) with 14-3-3 and FD1 proteins to induce the expression of flowering genes. In addition, two key pathways related to heading date, GI-Hd1-Hd3a and Ghd7-Ehd1-Hd3a/RFT1 are introduced in this review. We summarize proteins with histone modification functions, due to the modification of histone is also significant for heading date. The flowering time also extremely dependent on the environments, including nutrient availability, abiotic and biotic stresses, we argue the phenotypes of rice heading date under different extreme environments, as well. Lastly, we gather genes that are reported having a change in heading time, but their detail molecular regulation is still elusive. Thus, this review introduces heading time systematically, providing knowledge and ideas for researchers to study further the phenotype of heading time.

Chromium (Cr) is a serious environmental contaminant that drastically limited the crop yields. Nitric oxide (NO) and spermine (Spm) portrayal significance in improving the plant tolerance against abiotic stresses. Therefore, we investigate the protective efficacy of seed priming with NO (100μM) and/or Spm (0.01mM) in minimising the Cr-induced toxic effects in rice (Oryza sativa L.) plants. Our outcomes revealed that Cr alone treatments (100μM) notably reduced the seed germination rate, plant growth, photosynthetic apparatus, nutrients uptake and antioxidant defence system, but extra generation of reactive oxygen species (ROS). Interestingly, the combine applications of NO and Spm significantly reversed the Cr-induced toxic effects by reducing the Cr-accumulation, maintaining the nutrient balance, improving the germination indices, levels of photosynthetic pigments (chl a by 24.6%, chl b by 36.3%, chl (a+b ) by 57.2% and carotenoids by 79.4%), PSII, photosynthesis gas exchange parameters and total soluble sugar (74.9%) by improving antioxidative enzyme activities. As a result, NO+Spm lowered the accumulation of oxidative markers (H2 O2 by 93.9/70.4%, O2 ˙- by 86.3/69.9% and MDA by 97.2/73.7% in leaves/roots), electrolyte leakage (71.4% in leaves) and improved the plant growth traits. Based on these findings, it can be concluded that NO triggers Spm to minimise the Cr-accumulation and its adverse effects on rice plants. Additionally, combined treatments (NO+Spm) were more effective in minimising the Cr-induced toxic effects in comparison to NO and Spm alone treatments. Thus, co-exposure of NO and Spm may be utilised to boost rice tolerance under Cr stress conditions.

Ascorbic acid (AsA) and selenium nanoparticles (SeNPs) were versatile plant growth regulators, playing multiple roles in promoting plant growth under heavy metal stresses. This study aimed to evaluate the beneficial role of individual and combined effects of AsA and SeNPs on morpho-physio-biochemical traits of rice with or without chromium (Cr) amendment. The results indicated that Cr negatively affected plant biomass, gas exchange parameters, total soluble sugar, proline, relative water contents, and antioxidant-related gene expression via increasing reactive oxygen species (MDA, H2O2, O2•−) formation, resulting in plant growth reduction. The application of AsA and SeNPs, individually or in combination, decreased the uptake and translocation of Cr in rice seedlings, increased seedlings with tolerance to Cr toxicity, and significantly improved the rice seedling growth. Most notably, AsA + SeNP treatment strengthened the antioxidative defense system through ROS quenching and Cr detoxification. The results collectively suggested that the application of AsA and SeNPs alone or in combination had the potential to alleviate Cr toxicity in rice and possibly other crop species.

Chromium (Cr) is a venomous heavy metal and environmental concern which threatened the global food safety due to its carcinogenic and mutagenic effects on biological systems. Some researchers have investigated the ameliorative role of ZnO-NPs to manage heavy metal toxicity in agricultural systems; however, their protective role has never been explored. Therefore, the present research was performed to explore the protective role of ZnO-NPs application under severe Cr toxicity in soybean seedlings. Soybean seedlings were supplemented with 100 µM Cr stress which caused deleterious effects on seed germination, plant growth, biomass, photosynthetic rate, disturbed PSII system, total soluble sugar, total soluble protein, nutrient acquisition by increasing the lipid peroxidation, and electrolyte leakage. Moreover, Cr stress also negatively affected the enzymatic antioxidative activities (SOD, POD, and CAT), and non-enzymatic activities (GR, GSH, GSSH) activities in soybean seedlings due to increased metal accumulation. However, foliar spray of ZnO-NPs mitigated Cr stress by reducing root and shoot Cr uptake as well as plant concentration of oxidative stress markers (MDA and H2O2). Moreover, a higher biomass, altered enzymatic and non-enzymatic antioxidant activities and increased nutrient uptake was observed in ZnO-NPs treated plants. This protective role might be due to the competitive superiority of ZnO-NPs over Cr to use similar in-planta transport channels. Our results revealed that the application of ZnO-NPs can alleviate Cr toxicity in soybean and offers a sustainable solution of crop growth in Cr-contaminated agricultural soils.

Chromium (Cr) contamination of agricultural soils is a major threat to human and plant health worldwide and causes reductions in plant growth and crop yields. 24-epibrassinolide (EBL) and nitric oxide (NO) have been shown to ameliorate the reductions in growth caused by the stresses induced by heavy metals; however, the interactions between EBL and NO on the alleviation of Cr-induced phytotoxicity have been poorly studied. Hence, this study was undertaken to examine any beneficial effects of EBL (0.01 µM) and NO (100 µM), applied alone or in combination, on the mitigation of stress induced by Cr (100 µM) in soybean seedlings. Although EBL and NO applied alone reduced the toxic effects of Cr, the combined treatment had the greatest effect. Mitigation of Cr intoxication occurred via reduced Cr uptake and translocation and by ameliorating reductions in water contents, light-harvesting pigments, and other photosynthetic parameters. In addition, the two hormones increased the activity of enzymatic and non-enzymatic defense mechanisms increasing the scavenging of reactive oxygen species, thereby reducing membrane damage and electrolyte leakage. Furthermore, the hormones reduced the accumulation of the toxic compound, methylglyoxal, by amplifying activities of glyoxalase I and glyoxalase II. Thus, applications of NO and EBL can significantly mitigate Cr-phytotoxicity when cultivating soybean plants in Cr-contaminated soils. However, further more-in depth studies including field investigations parallel with calculations of cost to profit ratios and yield losses are requested to validate the effectiveness of NO and/or EBL for remediation agents in Cr-contaminated soils with using key biomarkers (i.e., oxidative stress, antioxidant defense, and osmoprotectants) involved in the uptake, accumulation, and attenuation of Cr toxicity tested in our study.

Nickel (Ni) stress adversely affects plant growth and biomass accumulation, posturing severe menace to crop production and food security. The current study aimed to determine the putative role of sodium nitroprusside (SNP) in mitigating Ni-induced phytotoxicity and identify the underlying defense mechanisms in maize, which are poorly understood. Our findings showed that SNP significantly augmented plant growth, biomass, and photosynthesis-related attributes (Fv/Fm, Fm, qP ETR, and ΦPSII) through diminishing Ni uptake and translocation in root and shoot tissues of maize under Ni stress conditions. In parallel, exogenous SNP substantially relieved maize seedlings from Ni-induced stress by enhancing enzymatic (SOD, CAT, and GPX) and non-enzymatic (phenol and flavonoids) antioxidant defenses and reducing oxidative stress indicators (MDA and H2 O2 ). The results revealed that SNP treatment increased the content of organic osmolyte glycine betaine and the activity of GST, concomitantly with ATP and ionic exchange capacity (including Ca2+ -ATPase and Mg2+ -ATPase), advocating its sufficiency to promote plant growth and avert Ni-induced stress in maize plants. The only exception was the production of organic acids (citric, oxalic, malic, and formic acids), which was reduced as SNP treatment relieved maize seedlings from Ni-induced oxidative damage. The application of SNP also displayed higher expression of defense- and detoxifying-related genes than in control treatments. Together, our data highlighted the mechanism involved in the amelioration of Ni toxicity by SNP; thus, suggesting a potential role of SNP in mitigating the adverse effects of Ni-contaminated soils to boost growth and yield of crop plants, that is, maize.

The bioavailability for varied-size phosphorus (P)-binding colloids (Pcoll) especially from external P sources in soil terrestrial ecosystems remains unclear. This study evaluated the differential contribution of various-sized biogas slurry (BS)-derived colloids to plant available P uptake in the rhizosphere and the corresponding patterns of phosphatase response. Keeping the same content of total P input (15 mg kg-1), we applied different size-fractioned BS-derived colloids including nanosized colloids (NCs, 1-20 nm), fine-sized colloids (FCs, 20-220 nm), and medium-sized colloids (MCs, 220-450 nm) respectively to conduct a 45-day rice (Oryza sativa L.) rhizotron experiment. During the whole cultivation period, the dynamics of chemical characteristics and P fractions in each experimental rhizosphere soil solution were analyzed. The spatial and temporal dynamics examination of P-transforming enzymes (acid phosphatases) in the rice rhizosphere was visualized by a soil zymography technique after 5, 25, and 45 days of rice transplantation. The results indicated that the acid phosphatase activities and its hot spot areas were significantly 1) correlated with the relative bioavailability of colloidal P (RBAcoll), 2) increased with the colloid-free (truly dissolved P) and BS-derived NC addition, and 3) affected by the plant growth stage. With the nanosized BS colloid addition, the RBAcoll and plant biomass were respectively found to be the highest (64% and 1.22 g plant-1), in which the acid phosphatase-catalyzed hydrolysis of organic Pcoll played an important role. All of the above suggested that nanosized BS-derived colloids are an effective alternative to conventional phosphorus fertilizer for promoting plant P uptake and P bioavailability.

The use of nanotechnology applications for the improvement of agriculture sectors is increasing day by day. Relative to conventional fertilizers, nano-fertilizers are promptly uptaken by plants and can enhance the plant's growth and development more efficiently. Thus, nanomaterials i.e. nanofibers, nano-fertilizers, and nano-pesticides can remarkably enhance the plants growth and yield production as well as disease resistance with limiting pathogenic attacks. Plant growth-promoting rhizobacteria (PGPR) are deliberated as beneficial soil bacteria which can boost the plants growth attributes in both direct and indirect ways. These bacteria can restrict the harmful impacts of chemical fertilizers as well as toxic compounds released in the soil as a result of industrialization. The inoculation of PGPR can be proved as an efficient technique to enhance the productivity of the agriculture sector with an environmentally friendly approach. The combined application of nanomaterials and PGPR could be a promising way to maintain crop development and productivity. Additionally, various nanomaterials such as titanium, gold, zeolites, carbon, zinc, silver, silica, etc. with PGPR have an auspicious effect on plant development. This book chapter will explore the novel combined strategy of nanotechnology and PGPR to promote crop productivity.