Abscisic acid prevents pollen abortion under high-temperature stress by mediating sugar metabolism in rice spikelets

A Next-Generation Combinatorial Genomic Strategy Scans Genomic Loci Governing Heat Stress Tolerance in Chickpea

In the wake of rising earth temperature, chickpea crop production is haunted by the productivity crisis. Chickpea, a cool season legume manifests tolerance in several agro-physiological level, which is complex quantitative in nature, and regulated by multiple genes and genetic networks. Understanding the molecular genetic basis of this tolerance and identifying key regulators can leverage chickpea breeding against heat stress. This study employed a genomics-assisted breeding strategy utilizing multi-locus GWAS to identify 10 key genomic regions linked to traits contributing to heat stress tolerance in chickpea. These loci subsequently delineated few key candidates and hub regulatory genes, such as RAD23b, CIPK25, AAE19, CK1 and WRKY40, through integrated genomics, transcriptomics and interactive analyses. The differential transcript accumulation of these identified candidates in contrasting chickpea accessions suggests their potential role in heat stress tolerance. Differential ROS accumulation along with their scavengers' transcript abundance aligning with the expression of identified candidates in the contrasting chickpea accessions persuade their regulatory significance. Additionally, their functional significance is ascertained by heterologous expression and subsequent heat stress screening. The high confidence genomic loci and the superior genes and natural alleles delineated here has great potential for swift genomic interventions to enhance heat resilience and yield stability in chickpea.

Abscisic Acid Regulates the Occurrence and Recovery of the Striped Leaf Phenotype in Response to Lacking Light at the Base of Sheath in Rice by Modulating Carbohydrate Metabolism

Rice B03S mutants with intermittent leaf discoloration were developed from the photoperiod- and thermosensitive genic male sterile (PTGMS) rice line Efeng 1S. After these plants were deeply transplanted, the new leaves manifested typical stripe patterns. In this study, deep and shallow transplantation of B03S was carried out, and aluminum shading was performed directly on the leaf sheath. It was determined that the reason for the appearance of the striped leaf trait was that the base of leaf sheath lacked light, at which time the sheath transformed from the source organ to the sink organ in rice. To elucidate the related metabolic changes in glycometabolism and abscisic acid (ABA) biosynthesis and transcriptional regulation in the leaf sheath, ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) combined with transcriptome and real-time quantitative PCR (qPCR) validation were used for analysis after deep and shallow transplantation. The result indicates that the leaf sheath may need to compete with the new leaves for sucrose produced by the photosynthesis of old leaves in response to lacking light at the base of sheath. Moreover, the ABA content increases in the leaf sheath when the gene expression of ABA2 and AAO1 is upregulated at the same time, enhancing the plant's resistance to the adverse condition of shading at the leaf sheath. Furthermore, exogenous spraying of B03S with ABA solution was carried out to help recovery under shading stress. The result indicates that the synthesis of endogenous ABA in the leaf sheath is reduced by spraying ABA. At the same time, ABA regulates sucrose metabolism by inhibiting the expression of the SUS gene. This allows for more sucrose synthesized by the old leaves to be transported to the new leaves, resulting an obvious recovery effect of the strip leaf character due to the re-balance of sugar supply and demand in B03S. These findings improve the understanding of the physiological function and metabolic mechanism of the rice leaf sheath, provide a theoretical basis for uneven leaf coloration in nature, and provide theoretical guidance for rice production via seedling transplantation or direct seeding.

Genome-wide identification of starch phosphorylase gene family in Rosa chinensis and expression in response to abiotic stress

Chinese rose (Rosa chinensis) is an important ornamental plant, with economic, cultural, and symbolic significance. During the application of outdoor greening, adverse environments such as high temperature and drought are often encountered, which affect its application scope and ornamental quality. The starch phosphorylase (Pho) gene family participate in the synthesis and decomposition of starch, not only related to plant energy metabolism, but also plays an important role in plant stress resistance. The role of Pho in combating salinity and high temperature stress in R. chinensis remains unknown. In this work, 4 Phos from R. chinensis were detected with Pfam number of Pho (PF00343.23) and predicted by homolog-based prediction (HBP). The Phos are characterized by sequence lengths of 821 to 997 bp, and the proteins are predicted to subcellularly located in the plastid and cytoplasm. The regulatory regions of the Phos contain abundant stress and phytohormone-responsive cis-acting elements. Based on transcriptome analysis, the Phos were found to respond to abiotic stress factors such as drought, salinity, high temperature, and plant phytohormone of jasmonic acid and salicylic acid. The response of Phos to abiotic stress factors such as salinity and high temperature was confirmed by qRT-PCR analysis. To evaluate the genetic characteristics of Phos, a total of 69 Phos from 17 species were analyzed and then classified into 3 groups in phylogenetic tree. The collinearity analysis of Phos in R. chinensis and other species was conducted for the first time. This work provides a view of evolution for the Pho gene family and indicates that Phos play an important role in abiotic stress response of R. chinensis.

Thiourea improves yield and quality traits of Brassica napus L. by upregulating the antioxidant defense system under high temperature stress

High temperature stress influences plant growth, seed yield, and fatty acid contents by causing oxidative damage. This study investigated the potential of thiourea (TU) to mitigate oxidative stress and restoring seed oil content and quality in canola. The study thoroughly examined three main factors: (i) growth conditions-control and high temperature stress (35 °C); (ii) TU supplementation (1000 mg/L)-including variations like having no TU, water application at the seedling stage, TU application at seedling stage (BBCH Scale-39), water spray at anthesis stage, and TU application at anthesis stage (BBCH Scale-60); (iii) and two canola genotypes, 45S42 and Hiola-401, were studied separately. High temperature stress reduced growth and tissue water content, as plant height and relative water contents were decreased by 26 and 36% in 45S42 and 27 and 42% Hiola-401, respectively, resulting in a substantial decrease in seed yield per plant by 36 and 38% in 45S42 and Hiola-401. Seed oil content and quality parameters were also negatively affected by high temperature stress as seed oil content was reduced by 32 and 35% in 45S42 and Hiola-401. High-temperature stress increased the plant stress indicators like malondialdehyde, H2O2 content, and electrolyte leakage; these indicators were increased in both canola genotypes as compared to control. Interestingly, TU supplementation restored plant performance, enhancing height, relative water content, foliar chlorophyll (SPAD value), and seed yield per plant by 21, 15, 30, and 28% in 45S42; 19, 13, 26, and 21% in Hiola-401, respectively, under high temperature stress as compared to control. In addition, seed quality, seed oil content, linoleic acid, and linolenic acid were improved by 16, 14, and 22% in 45S42, and 16, 11, and 23% in Hiola-401, as compared to control. The most significant improvements in canola seed yield per plant were observed when TU was applied at the anthesis stage. Additionally, the research highlighted that canola genotype 45S42 responded better to TU applications and exhibited greater resilience against high temperature stress compared to genotype Hiola-401. This interesting study revealed that TU supplementation, particularly at the anthesis stage, improved high temperature stress tolerance, seed oil content, and fatty acid profile in two canola genotypes.

Effects of exogenous glycine betaine on growth and development of tomato seedlings under cold stress

Low temperature is a type of abiotic stress affecting the tomato (Solanum lycopersicum) growth. Understanding the mechanisms and utilization of exogenous substances underlying plant tolerance to cold stress would lay the foundation for improving temperature resilience in this important crop. Our study is aiming to investigate the effect of exogenous glycine betaine (GB) on tomato seedlings to increase tolerance to low temperatures. By treating tomato seedlings with exogenous GB under low temperature stress, we found that 30 mmol/L exogenous GB can significantly improve the cold tolerance of tomato seedlings. Exogenous GB can influence the enzyme activity of antioxidant defense system and ROS levels in tomato leaves. The seedlings with GB treatment presented higher Fv/Fm value and photochemical activity under cold stress compared with the control. Moreover, analysis of high-throughput plant phenotyping of tomato seedlings also supported that exogenous GB can protect the photosynthetic system of tomato seedlings under cold stress. In addition, we proved that exogenous GB significantly increased the content of endogenous abscisic acid (ABA) and decreased endogenous gibberellin (GA) levels, which protected tomatoes from low temperatures. Meanwhile, transcriptional analysis showed that GB regulated the expression of genes involved in antioxidant capacity, calcium signaling, photosynthesis activity, energy metabolism-related and low temperature pathway-related genes in tomato plants. In conclusion, our findings indicated that exogenous GB, as a cryoprotectant, can enhance plant tolerance to low temperature by improving the antioxidant system, photosynthetic system, hormone signaling, and cold response pathway and so on.

Genome-Wide Identification of PYL/RCAR ABA Receptors and Functional Analysis of LbPYL10 in Heat Tolerance in Goji (Lycium barbarum)

The characterization of the PYL/RCAR ABA receptors in a great deal of plant species has dramatically advanced the study of ABA functions involved in key physiological processes. However, the genes in this family are still unclear in Lycium (Goji) plants, one of the well-known economically, medicinally, and ecologically valuable fruit crops. In the present work, 12 homologs of Arabidopsis PYL/RCAR ABA receptors were first identified and characterized from Lycium (L.) barbarum (LbPYLs). The quantitative real-time PCR (qRT-PCR) analysis showed that these genes had clear tissue-specific expression patterns, and most of them were transcribed in the root with the largest amount. Among the three subfamilies, while the Group I and Group III members were down-regulated by extraneous ABA, the Group II members were up-regulated. At 42 °C, most transcripts showed a rapid and violent up-regulation response to higher temperature, especially members of Group II. One of the genes in the Group II members, LbPYL10, was further functionally validated by virus-induced gene silencing (VIGS) technology. LbPYL10 positively regulates heat stress tolerance in L. barbarum by alleviating chlorophyll degradation, thus maintaining chlorophyll stability. Integrating the endogenous ABA level increase following heat stress, it may be concluded that LbPYL-mediated ABA signaling plays a vital role in the thermotolerance of L. barbarum plants. Our results highlight the strong potential of LbPYL genes in breeding genetically modified L. barbarum crops that acclimate to climate change.

Plants and global warming: challenges and strategies for a warming world

KEY MESSAGE

In this review, we made an attempt to create a holistic picture of plant response to a rising temperature environment and its impact by covering all aspects from temperature perception to thermotolerance. This comprehensive account describing the molecular mechanisms orchestrating these responses and potential mitigation strategies will be helpful for understanding the impact of global warming on plant life. Organisms need to constantly recalibrate development and physiology in response to changes in their environment. Climate change-associated global warming is amplifying the intensity and periodicity of these changes. Being sessile, plants are particularly vulnerable to variations happening around them. These changes can cause structural, metabolomic, and physiological perturbations, leading to alterations in the growth program and in extreme cases, plant death. In general, plants have a remarkable ability to respond to these challenges, supported by an elaborate mechanism to sense and respond to external changes. Once perceived, plants integrate these signals into the growth program so that their development and physiology can be modulated befittingly. This multifaceted signaling network, which helps plants to establish acclimation and survival responses enabled their extensive geographical distribution. Temperature is one of the key environmental variables that affect all aspects of plant life. Over the years, our knowledge of how plants perceive temperature and how they respond to heat stress has improved significantly. However, a comprehensive mechanistic understanding of the process still largely elusive. This review explores how an increase in the global surface temperature detrimentally affects plant survival and productivity and discusses current understanding of plant responses to high temperature (HT) and underlying mechanisms. We also highlighted potential resilience attributes that can be utilized to mitigate the impact of global warming.

Exogenous abscisic acid improves grain filling capacity under heat stress by enhancing antioxidative defense capability in rice

BACKGROUND

Heat stress is a major restrictive factor that causes yield loss in rice. We previously reported the priming effect of abscisic acid (ABA) on rice for enhanced thermotolerance at the germination, seedling and heading stages. In the present study, we aimed to understand the priming effect and mechanism of ABA on grain filling capacity in rice under heat stress.

RESULTS

Rice plants were pretreated with distilled water, 50 μM ABA and 10 μM fluridone by leaf spraying at 8 d or 15 d after initial heading (AIH) stage and then were subjected to heat stress conditions of 38 °C day/30 °C night for 7 days, respectively. Exogenous ABA pretreatment significantly super-activated the ABA signaling pathway and improved the SOD, POD, CAT and APX enzyme activity levels, as well as upregulated the ROS-scavenging genes; and decreased the heat stress-induced ROS content (O2- and H2O2) by 15.0-25.5% in rice grain under heat stress. ABA pretreatment also increased starch synthetase activities in rice grain under heat stress. Furthermore, ABA pretreatment significantly improved yield component indices and grain yield by 14.4-16.5% under heat stress. ABA pretreatment improved the milling quality and the quality of appearance and decreased the incidence of chalky kernels and chalkiness in rice grain and improved the rice grain cooking quality by improving starch content and gel consistence and decreasing the amylose percentage under heat stress. The application of paraquat caused overaccumulation of ROS, decreased starch synthetase activities and ultimately decreased starch content and grain yield. Exogenous antioxidants decreased ROS overaccumulation and increased starch content and grain yield under heat stress.

CONCLUSION

Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing rice grain filling capacity under heat stress at grain filling stage mainly by inhibiting ROS overaccumulation and improving starch synthetase activities in rice grain.

From the floret to the canopy: High temperature tolerance during flowering

Heat waves induced by climate warming have become common in food-producing regions worldwide, frequently coinciding with high temperature (HT)-sensitive stages of many crops and thus threatening global food security. Understanding the HT sensitivity of reproductive organs is currently of great interest for increasing seed set. The responses of seed set to HT involve multiple processes in both male and female reproductive organs, but we currently lack an integrated and systematic summary of these responses for the world's three leading food crops (rice, wheat, and maize). In the present work, we define the critical high temperature thresholds for seed set in rice (37.2°C ± 0.2°C), wheat (27.3°C ± 0.5°C), and maize (37.9°C ± 0.4°C) during flowering. We assess the HT sensitivity of these three cereals from the microspore stage to the lag period, including effects of HT on flowering dynamics, floret growth and development, pollination, and fertilization. Our review synthesizes existing knowledge about the effects of HT stress on spikelet opening, anther dehiscence, pollen shedding number, pollen viability, pistil and stigma function, pollen germination on the stigma, and pollen tube elongation. HT-induced spikelet closure and arrest of pollen tube elongation have a catastrophic effect on pollination and fertilization in maize. Rice benefits from pollination under HT stress owing to bottom anther dehiscence and cleistogamy. Cleistogamy and secondary spikelet opening increase the probability of pollination success in wheat under HT stress. However, cereal crops themselves also have protective measures under HT stress. Lower canopy/tissue temperatures compared with air temperatures indicate that cereal crops, especially rice, can partly protect themselves from heat damage. In maize, husk leaves reduce inner ear temperature by about 5°C compared with outer ear temperature, thereby protecting the later phases of pollen tube growth and fertilization processes. These findings have important implications for accurate modeling, optimized crop management, and breeding of new varieties to cope with HT stress in the most important staple crops.

Disruption of the Contents of Endogenous Hormones Cause Pollen Development Obstruction and Abortion in Male-Sterile Hybrid Lily Populations

Lilies are well-known flowers with large anthers and a high quantity of pollen that easily contaminates clothing and tepals. The anthers need to be artificially removed, leading to production problems. Cultivating male-sterile or pollen-free lilies could solve these problems. The key period of male sterility in a specific male-sterile hybrid lily population was determined through cytological observation. The contents of hormones, soluble sugar, soluble protein, and proline were determined by high-performance liquid chromatography, tandem mass spectrometry and colorimetry. Transcriptome sequencing was used to identify the genes with altered expression. The key period of male sterility was determined to be the microspore mother and tetrad stages. The hormone contents were abnormal in the sterile line compared with the fertile line. The indole-3-acetic acid (IAA) content was higher in the sterile line than in the fertile line at all stages, while the gibberellic acid 4 (GA4) content showed the opposite result. Abscisic acid (ABA) accumulated in the sterile line in both the microspore mother and tetrad stages, and the zeatin riboside (ZR) content in the sterile line increased at the microspore mother stage but decreased at the tetrad stage. The contents of soluble sugar, soluble protein and proline were higher in the fertile line than in the sterile line. Genes involved in auxin and ABA synthesis and signalling pathways were highly expressed in the male-sterile line. Our data suggested that abnormal contents of hormones in the microspore mother and tetrad stages resulted in pollen abortion in a male-sterile hybrid lily population, which indicated that the hormone balance in specific stages plays critical functions in pollen development in lilies.

Examining the Transcriptomic and Biochemical Signatures of Bacillus subtilis Strains: Impacts on Plant Growth and Abiotic Stress Tolerance

Rhizobacteria from various ecological niches display variations in physiological characteristics. This study investigates the transcriptome profiling of two Bacillus subtilis strains, BsCP1 and BsPG1, each isolated from distinct environments. Gene expression linked to the synthesis of seven types of antibiotic compounds was detected in both BsCP1 and BsPG1 cultures. Among these, the genes associated with plipastatin synthesis were predominantly expressed in both bacterial strains. However, genes responsible for the synthesis of polyketide, subtilosin, and surfactin showed distinct transcriptional patterns. Additionally, genes involved in producing exopolysaccharides (EPS) showed higher expression levels in BsPG1 than in BsCP1. Consistently with this, a greater quantity of EPS was found in the BsPG1 culture compared to BsCP1. Both bacterial strains exhibited similar effects on Arabidopsis seedlings, promoting root branching and increasing seedling fresh weight. However, BsPG1 was a more potent enhancer of drought, heat, and copper stress tolerance than BsCP1. Treatment with BsPG1 had a greater impact on improving survival rates, increasing starch accumulation, and stabilizing chlorophyll content during the post-stress stage. qPCR analysis was used to measure transcriptional changes in Arabidopsis seedlings in response to BsCP1 and BsPG1 treatment. The results show that both bacterial strains had a similar impact on the expression of genes involved in the salicylic acid (SA) and jasmonic acid (JA) signaling pathways. Likewise, genes associated with stress response, root development, and disease resistance showed comparable responses to both bacterial strains. However, treatment with BsCP1 and BsPG1 induced distinct activation of genes associated with the ABA signaling pathway. The results of this study demonstrate that bacterial strains from different ecological environments have varying abilities to produce beneficial metabolites for plant growth. Apart from the SA and JA signaling pathways, ABA signaling triggered by PGPR bacterial strains could play a crucial role in building an effective resistance to various abiotic stresses in the plants they colonize.

Artificial warming affects sugar signals and flavonoid accumulation to improve female willows' growth faster than males

Increasing global warming is severely affecting tree growth and development. However, research on the sex-specific responses of dioecious trees to warming is scarce. Here, male and female Salix paraplesia were selected for artificial warming (an increase of 4 °C relative to ambient temperature) to investigate the effects on morphological, physiological, biochemical and molecular responses. The results showed that warming significantly promoted the growth of female and male S. paraplesia, but females grew faster than males. Warming affected photosynthesis, chloroplast structures, peroxidase activity, proline, flavonoids, nonstructural carbohydrates (NSCs) and phenolic contents in both sexes. Interestingly, warming increased flavonoid accumulation in female roots and male leaves but inhibited it in female leaves and male roots. The transcriptome and proteome results indicated that differentially expressed genes and proteins were significantly enriched in sucrose and starch metabolism and flavonoid biosynthesis pathways. The integrative analysis of transcriptomic, proteomic, biochemical and physiological data revealed that warming changed the expression of SpAMY, SpBGL, SpEGLC and SpAGPase genes, resulting in the reduction of NSCs and starch and the activation of sugar signaling, particularly SpSnRK1s, in female roots and male leaves. These sugar signals subsequently altered the expression of SpHCTs, SpLAR and SpDFR in the flavonoid biosynthetic pathway, ultimately leading to the differential accumulation of flavonoids in female and male S. paraplesia. Therefore, warming causes sexually differential responses of S. paraplesia, with females performing better than males.

MaABI5 and MaABF1 transcription factors regulate the expression of MaJOINTLESS during fruit abscission in mulberry (Morus alba L.)

Mulberry holds significant economic value. However, during the ripening stage of its fruit, the phenomenon of abscission, resulting in heavy fruit drop, can severely impact the yield. The formation of off-zone structures is a critical factor in the fruit abscission process, and this process is regulated by multiple transcription factors. One such key gene that plays a significant role in the development of the off-zone in the model plant tomato is JOINTLESS, which promotes the expression of abscission-related genes and regulates the differentiation of abscission zone tissue cells. However, there is a lack of information about fruit abscission mechanism in mulberry. Here, we analyzed the MaJOINTLESS promoter and identified the upstream regulators MaABF1 and MaABI5. These two regulators showed binding with MaJOINTLESS promoter MaABF1 (the ABA Binding Factor/ABA-Responsive Element Binding Proteins) activated the expression of MaJOINTLESS, while MaABI5 (ABSCISIC ACID-INSENSITIVE 5) inhibited the expression of MaJOINTLESS. Finally, the differentially expressed genes (DEGs) were analyzed by transcriptome sequencing to investigate the expression and synergistic relationship of endogenous genes in mulberry during abscission. GO classification and KEGG pathway enrichment analysis showed that most of the DEGs were concentrated in MAPK signaling pathway, flavonoid biosynthesis, citric acid cycle, phytohormone signaling, amino acid biosynthesis, and glycolysis. These results provide a theoretical basis for subsequent in-depth study of physiological fruit abscission in mulberry.

Integrated transcriptome, proteome and metabolome analyses revealed secondary metabolites and auxiliary carbohydrate metabolism augmenting drought tolerance in rice

Drought is one of the major consequences of climate change and a serious threat to rice production. Drought stress activates interactions among genes, proteins and metabolites at the molecular level. A comparative multi-omics analysis of drought-tolerant and drought-sensitive rice cultivars can decipher the molecular mechanisms involved in drought tolerance/response. Here, we characterized the global-level transcriptome, proteome, and metabolome profiles, and performed integrated analyses thereof in a drought-sensitive (IR64) and a drought-tolerant (Nagina 22) rice cultivar under control and drought-stress conditions. The transcriptional dynamics and its integration with proteome analysis revealed the role of transporters in regulation of drought stress. The proteome response illustrated the contribution of translational machinery to drought tolerance in N22. The metabolite profiling revealed that aromatic amino acids and soluble sugars contribute majorly to drought tolerance in rice. The integrated transcriptome, proteome and metabolome analysis performed using statistical and knowledge-based methods revealed the preference for auxiliary carbohydrate metabolism through glycolysis and pentose phosphate pathway contributed to drought tolerance in N22. In addition, L-phenylalanine and the genes/proteins responsible for its biosynthesis were also found to contribute to drought tolerance in N22. In conclusion, our study provided mechanistic insights into the drought response/adaptation mechanism and is expected to facilitate engineering of drought tolerance in rice.

The Essential Role of H2S-ABA Crosstalk in Maize Thermotolerance through the ROS-Scavenging System

Hydrogen sulfide (H2S) and abscisic acid (ABA), as a signaling molecule and stress hormone, their crosstalk-induced thermotolerance in maize seedlings and its underlying mechanism were elusive. In this paper, H2S and ABA crosstalk as well as the underlying mechanism of crosstalk-induced thermotolerance in maize seedlings were investigated. The data show that endogenous levels of H2S and ABA in maize seedlings could be mutually induced by regulating their metabolic enzyme activity and gene expression under non-heat stress (non-HS) and HS conditions. Furthermore, H2S and ABA alone or in combination significantly increase thermotolerance in maize seedlings by improving the survival rate (SR) and mitigating biomembrane damage. Similarly, the activity of the reactive oxygen species (ROS)-scavenging system, including enzymatic antioxidants catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POD), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and superoxide dismutase (SOD), as well as the non-enzymatic antioxidants reduced ascorbic acid (AsA), carotenoids (CAR), flavone (FLA), and total phenols (TP), was enhanced by H2S and ABA alone or in combination in maize seedlings. Conversely, the ROS level (mainly hydrogen peroxide and superoxide radical) was weakened by H2S and ABA alone or in combination in maize seedlings under non-HS and HS conditions. These data imply that the ROS-scavenging system played an essential role in H2S-ABA crosstalk-induced thermotolerance in maize seedlings.

Overexpression of Rice Histone H1 Gene Reduces Tolerance to Cold and Heat Stress

Temperature stresses, including low- and high-temperature stresses, are the main abiotic stresses affecting rice yield. Due to global climate change, the impact of temperature pressure on rice yield is gradually increasing, which is also a major concern for researchers. In this study, an H1 histone in Oryza sativa (OsHis1.1, LOC_Os04g18090) was cloned, and its role in rice's response to temperature stresses was functionally characterized. The GUS staining analysis of OsHis1.1 promoter-GUS transgenic rice showed that OsHis1.1 was widely expressed in various rice tissues. Transient expression demonstrated that OsHis1.1 was localized in the nucleus. The overexpression of OsHis1.1 reduces the tolerance to temperature stress in rice by inhibiting the expression of genes that are responsive to heat and cold stress. Under stress conditions, the POD activity and chlorophyll and proline contents of OsHis1.1-overexpression rice lines were significantly lower than those of the wild type, while the malondialdehyde content was higher than that of the wild type. Compared with Nip, OsHis1.1-overexpression rice suffered more serious oxidative stress and cell damage under temperature stress. Furthermore, OsHis1.1-overexpression rice showed changes in agronomic traits.

Anatomy and Comparative Transcriptome Reveal the Mechanism of Male Sterility in Salvia miltiorrhiza

Salvia miltiorrhiza Bunge is an important traditional herb. Salvia miltiorrhiza is distributed in the Sichuan province of China (here called SC). Under natural conditions, it does not bear seeds and its sterility mechanism is still unclear. Through artificial cross, there was defective pistil and partial pollen abortion in these plants. Electron microscopy results showed that the defective pollen wall was caused by delayed degradation of the tapetum. Due to the lack of starch and organelle, the abortive pollen grains showed shrinkage. RNA-seq was performed to explore the molecular mechanisms of pollen abortion. KEGG enrichment analysis suggested that the pathways of phytohormone, starch, lipid, pectin, and phenylpropanoid affected the fertility of S. miltiorrhiza. Moreover, some differentially expressed genes involved in starch synthesis and plant hormone signaling were identified. These results contribute to the molecular mechanism of pollen sterility and provide a more theoretical foundation for molecular-assisted breeding.

Enhancing heat stress tolerance in Lanzhou lily (Lilium davidii var. unicolor) with Trichokonins isolated from Trichoderma longibrachiatum SMF2

Lanzhou lily (Lilium davidii var. unicolor) is a renowned edible crop produced in China and relatively sensitive to high temperature (HT). Trichokonins (TKs) are antimicrobial peptaibols secreted from Trichoderma longibrachiatum strain SMF2. Here, we report that TKs application improves the thermotolerance of Lanzhou lily. The activity of the antioxidant enzyme system (SOD, CAT, and POD), the level of heat-resistance-associated phytohormones (ABA, SA, and JA), the relative water content (RWC), the content of chlorophyll (Chl), and the net photosynthetic rate (P _n) were promoted by TKs treatment in Lanzhou lily plants subjected to heat stress (HS). TKs treatment also mitigated cell injury as shown by a lower accumulation of malondialdehyde (MDA) and relative electrolyte leakage (REL) under HS conditions. RNA-seq data analysis showed that more than 4.5 times differentially expressed genes (DEGs) responded to TKs treatment under HS compared to non-HS, and TKs treatment reduced protein folding and enhanced cellular repair function under HS conditions. The analyses of DEGs involved in hormone (ABA, SA and JA) synthesis and signaling pathways suggested that TKs might improve Lanzhou lily heat tolerance by promoting ABA synthesis and signal transduction. TKs highly induced DEGs of the HSF-HSP pathway under HS, in which HSFA2 accounted for most of the HSF family. Furthermore, TKs treatment resulted in the upregulation of heat-protective genes LzDREB2B, LzHsfA2a, LzMBF1c, LzHsp90, and LzHsp70 involved in HSF-HSP signal pathway after long-term HS. LzHsfA2a-1 likely plays a key role in acquisition of TKs-induced thermotolerance of Lanzhou lily as evidenced by the sustained response to HS, the enhanced response to TKs treatment under long-term HS, and the high sequence similarity to LlHsfA2a which is a key regulator for the improvement of heat tolerance in Lilium longiflorum. Our results reveal the underlying mechanisms of TKs-mediated thermotolerance in Lanzhou lily and highlight an attractive approach to protecting crop plants from damage caused by HS in a global warming future.

Abiotic Stress in Crop Production

The vast majority of agricultural land undergoes abiotic stress that can significantly reduce agricultural yields. Understanding the mechanisms of plant defenses against stresses and putting this knowledge into practice is, therefore, an integral part of sustainable agriculture. In this review, we focus on current findings in plant resistance to four cardinal abiotic stressors—drought, heat, salinity, and low temperatures. Apart from the description of the newly discovered mechanisms of signaling and resistance to abiotic stress, this review also focuses on the importance of primary and secondary metabolites, including carbohydrates, amino acids, phenolics, and phytohormones. A meta-analysis of transcriptomic studies concerning the model plant Arabidopsis demonstrates the long-observed phenomenon that abiotic stressors induce different signals and effects at the level of gene expression, but genes whose regulation is similar under most stressors can still be traced. The analysis further reveals the transcriptional modulation of Golgi-targeted proteins in response to heat stress. Our analysis also highlights several genes that are similarly regulated under all stress conditions. These genes support the central role of phytohormones in the abiotic stress response, and the importance of some of these in plant resistance has not yet been studied. Finally, this review provides information about the response to abiotic stress in major European crop plants—wheat, sugar beet, maize, potatoes, barley, sunflowers, grapes, rapeseed, tomatoes, and apples.

RGA1 alleviates low-light-repressed pollen tube elongation by improving the metabolism and allocation of sugars and energy

Low-light stress compromises photosynthetic and energy efficiency and leads to spikelet sterility; however, the effect of low-light stress on pollen tube elongation in the pistil remains poorly understood. The gene RGA1, which encodes a Gα-subunit of the heterotrimeric G-protein, enhanced low-light tolerance at anthesis by preventing the cessation of pollen tube elongation in the pistil of rice plants. In this process, marked increases in the activities of acid invertase (INV), sucrose synthase (SUS) and mitochondrial respiratory electron transport chain complexes, as well as the relative expression levels of SUTs (sucrose transporter), SWEETs (sugars will eventually be exported transporters), SUSs, INVs, CINs (cell-wall INV 1), SnRK1A (sucrose-nonfermenting 1-related kinase 1) and SnRK1B, were observed in OE-1 plants. Accordingly, notable increases in contents of ATP and ATPase were presented in OE-1 plants under low-light conditions, while they were decreased in d1 plants. Importantly, INV and ATPase activators (sucrose and Na₂ SO₃ , respectively) increased spikelet fertility by improving the energy status in the pistil under low-light conditions, and the ATPase inhibitor Na₂ VO₄ induced spikelet sterility and decreased ATPase activity. These results suggest that RGA1 could alleviate the low-light stress-induced impairment of pollen tube elongation to increase spikelet fertility by promoting sucrose unloading in the pistil and improving the metabolism and allocation of energy.

The hot science in rice research: How rice plants cope with heat stress

Global climate change has great impacts on plant growth and development, reducing crop productivity worldwide. Rice (Oryza sativa L.), one of the world's most important food crops, is susceptible to high-temperature stress from seedling stage to reproductive stage. In this review, we summarize recent advances in understanding the molecular mechanisms underlying heat stress responses in rice, including heat sensing and signalling, transcriptional regulation, transcript processing, protein translation, and post-translational regulation. We also highlight the irreversible effects of high temperature on reproduction and grain quality in rice. Finally, we discuss challenges and opportunities for future research on heat stress responses in rice.

How rice adapts to high temperatures

High-temperature stress affects crop yields worldwide. Identifying thermotolerant crop varieties and understanding the basis for this thermotolerance would have important implications for agriculture, especially in the face of climate change. Rice (Oryza sativa) varieties have evolved protective strategies to acclimate to high temperature, with different thermotolerance levels. In this review, we examine the morphological and molecular effects of heat on rice in different growth stages and plant organs, including roots, stems, leaves and flowers. We also explore the molecular and morphological differences among thermotolerant rice lines. In addition, some strategies are proposed to screen new rice varieties for thermotolerance, which will contribute to the improvement of rice for agricultural production in the future.

OsGRF4AA compromises heat tolerance of developing pollen grains in rice

Extreme high temperature at the meiosis stage causes a severe decrease in spikelet fertility and grain yield in rice. The rice variety grain size on chromosome 2 (GS2) contains sequence variations of OsGRF4 (Oryza sativa growth-regulating factor 4; OsGRF4^AA ), escaping the microRNA miR396-mediated degradation of this gene at the mRNA level. Accumulation of OsGRF4 enhances nitrogen usage and metabolism, and increases grain size and grain yield. In this study, we found that pollen viability and seed-setting rate under heat stress (HS) decreased more seriously in GS2 than in its comparator, Zhonghua 11 (ZH11). Transcriptomic analysis revealed that, following HS, genes related to carbohydrate metabolic processes were expressed and regulated differentially in the anthers of GS2 and ZH11. Moreover, the expression of genes involved in chloroplast development and photosynthesis, lipid metabolism, and key transcription factors, including eight male sterile genes, were inhibited by HS to a greater extent in GS2 than in ZH11. Interestingly, pre-mRNAs of OsGRF4, and a group of essential genes involved in development and fertilization, were differentially spliced in the anthers of GS2 and ZH11. Taken together, our results suggest that variation in OsGRF4 affects proper transcriptional and splicing regulation of genes under HS, and that this can be mediated by, and also feed back to, carbohydrate and nitrogen metabolism, resulting in a reduction in the heat tolerance of rice anthers.

Transcriptomic insights into the effects of abscisic acid on the germination of Magnolia sieboldii K. Koch seed

Magnolia sieboldii K. Koch is a deciduous tree species. However, the wild resource of M. sieboldii has been declining due to excessive utilization and seed dormancy. In our previous research, M. sieboldii seeds have morphophysiological dormancy and low germination rates under natural conditions. The aim of the present study was to identify the genes involved in dormancy maintenance. In this study, the germination percentage of M. sieboldii seeds negatively correlated with the content of endogenous abscisic acid (ABA). The hydration of seeds for germination showed three distinct phases. Five key time points were identified: 0 h imbibition (dry seed, GZ), 0 day after imbibition (DAI), 16 DAI, 40 DAI, and 56 DAI. The comprehensive transcript profiles of M. sieboldii seeds treated with ABA and water at the five key germinating stages were obtained. A total of 9641 differentially expressed genes (DEGs) were identified, and 208 and 197 common DEGs were found throughout the ABA and water treatments, respectively. Compared with that in the GZ, 518, 696, 2133, and 1535 DEGs were identified in the SH group at 0, 16, 40 and 56 DAI, respectively. 666, 1725, 1560 and 1415 DEGs were identified in the ABA group at 0, 16, 40, and 56 DAI, respectively. Among the identified DEGs, 12 722 were annotated with GO terms, the top three enriched GO terms were different among the DEGs at 56 DAI in the ABA vs. SH treatments. KEGG pathway enrichment analysis for DEGs indicated that oxidative phosphorylation, protein processing in endoplasmic reticulum, starch and sucrose metabolism play an important role in seed response to ABA. 1926 TFs are obtained and classified into 72 families from the M. sieboldii transcriptome. Results of differential gene expression analysis together with qRT-PCR indicated that phase II is crucial for rapid and successful seed germination. This study is the first to present the global expression patterns of ABA-regulated transcripts in M. sieboldii seeds at different germinating phases.

The SAH7 Homologue of the Allergen Ole e 1 Interacts with the Putative Stress Sensor SBP1 (Selenium-Binding Protein 1) in Arabidopsis thaliana

In this study, we focused on a member of the Ole e 1 domain-containing family, AtSAH7, in Arabidopsis thaliana. Our lab reports for the first time on this protein, AtSAH7, that was found to interact with Selenium-binding protein 1 (AtSBP1). We studied by GUS assisted promoter deletion analysis the expression pattern of AtSAH7 and determined that the sequence 1420 bp upstream of the transcription start can act as a minimal promoter inducing expression in vasculature tissues. Moreover, mRNA levels of AtSAH7 were acutely increased under selenite treatment in response to oxidative stress. We confirmed the aforementioned interaction in vivo, in silico and in planta. Following a bimolecular fluorescent complementation approach, we determined that the subcellular localization of the AtSAH7 and the AtSAH7/AtSBP1 interaction occur in the ER. Our results indicate the participation of AtSAH7 in a biochemical network regulated by selenite, possibly associated with responses to ROS production.

Foliar application of selenium affecting pollen viability, grain chalkiness, and transporter genes in cadmium accumulating rice cultivar: A pot study

Under Cadmium (Cd) stress, rice grain quality and quantity are compromised, affecting human health. Application of Selenium (Se) mitigating Cd stress in rice was already reported, but its role in rescuing Cd induced damage in the reproductive parts in rice plants has not been studied before. To investigate the underlying mechanism, Se mediated alleviation of Cd-stress induced damage to pollen viability, germination rate, and grain chalkiness were studied. A grain Cd accumulating rice genotype was selected and treated with 10 μM Cd and sprayed with 5 μM Se during tillering, elongating and heading stages. A significant reduction in pollen viability, germination percentage, and accumulation of higher amount of ROS in the reproductive parts were observed in Cd treated plants. However, Se supplementation (i.e. Cd + Se), decreased the ROS accumulation in anther, pistil, pollen and enhanced the pollen viability and germination percentage. Cd translocation was prevented from flag leaf to grains, under Se treatment. As a result, a significantly higher seed setting rate, and yield were observed. Additionally, Se improved grain nutrient content and grain quality. Therefore, the recent study suggests that the use of foliar spray of Se could be a cost-effective strategy to prevent Cd-induced yield loss and quality in rice.

Strategies for indica rice adapted to high-temperature stress in the middle and lower reaches of the Yangtze River

High temperatures caused by climate warming severely affect the grain yield and quality of rice. In this study, the rice cultivars Longliangyou Huazhan (LLYHZ) and Quanliangyou 2118 (QLY2118) were selected as the experimental materials for investigation of an optimal cultivation system under high-temperature treatment. In addition, the heat-resistant cultivar Huanghuazhan (HHZ) and heat-sensitive cultivar Huiliangyou 858 (HLY858) were chosen as the experimental materials to study the effects of exogenous plant growth regulators on heat stress responses under high-temperature treatment. The results showed that mechanical transplanting of carpet seedlings and delayed sowing effectively increased the leaf area index and reduced the canopy temperature of LLYHZ and QLY2118. Furthermore, carpet seedling mechanical transplantation and delayed sowing improved grain yield and quality. Spray application of five plant growth regulators revealed that brassinolide and salicylic acid had the strongest effects on significantly improving antioxidant enzyme activities in the panicle, which would reduce the damage caused by the accumulation of reactive oxygen species and enhance plant tolerance of high-temperature stress. In addition, brassinolide and salicylic acid enhanced the percentage of anther dehiscence and percentage seed set. In this study, a set of simplified eco-friendly cultivation techniques for single-season indica rice adaptation to high-temperature stress was established. These results will be of great importance in alleviating the effects of high-temperature stress on rice production.

Oligomeric Proanthocyanidins Confer Cold Tolerance in Rice through Maintaining Energy Homeostasis

Oligomeric proanthocyanidins (OPCs) are abundant polyphenols found in foods and botanicals that benefit human health, but our understanding of the functions of OPCs in rice plants is limited, particularly under cold stress. Two rice genotypes, named Zhongzao39 (ZZ39) and its recombinant inbred line RIL82, were subjected to cold stress. More damage was caused to RIL82 by cold stress than to ZZ39 plants. Transcriptome analysis suggested that OPCs were involved in regulating cold tolerance in the two genotypes. A greater increase in OPCs content was detected in ZZ39 than in RIL82 plants under cold stress compared to their respective controls. Exogenous OPCs alleviated cold damage of rice plants by increasing antioxidant capacity. ATPase activity was higher and poly (ADP-ribose) polymerase (PARP) activity was lower under cold stress in ZZ39 than in RIL82 plants. Importantly, improvements in cold tolerance were observed in plants treated with the OPCs and 3-aminobenzamide (PARP inhibitor, 3ab) combination compared to the seedling plants treated with H₂O, OPCs, or 3ab alone. Therefore, OPCs increased ATPase activity and inhibited PARP activity to provide sufficient energy for rice seedling plants to develop antioxidant capacity against cold stress.

M, Paudel K. Influence of high-temperature stress on rice growth and development. A review

High-temperature stress (HS) has become an alarming threat to the global food system. Rice, an important crop that supports almost half of the global population, is vulnerable to heat stress. Under the influence of HS, it shows various physiological and morphological symptoms that increase spikelet sterility, reduce grain yield, and even cause total crop failure. HS affects growth and yield in two ways: hindrance in the process of pollination and fertilization and reduction of the grain weight. The former is caused by (i) distortion of floral organs, (ii) tapetum degeneration, (iii) low pollen protein concentration, (iv) decline in pollen viability, (v) reduction in dehiscence of anther, (vi) low pollen dispersal, (vii) decrease in number of pollens on stigma, (viii) reduction in pollen grain germination, (ix) hindrance in extension of pollen tubes, and (x) shrinkage of stigma which ultimately cause spikelet infertility. The latter is caused by (i)reduced photosynthetic rate, (ii) a boost in senescence of functional leaves, (iii) reduction of biological synthesis of starch, (iv)reduced starch augmentation, (v) shrunk duration of grain filling, and (vi) declined grain weight which ultimately reduce the grain yield. However, some agronomic and breeding approaches have been adopted for developing thermo-resistant cultivars but the success is limited. In this paper, we have summarized the the morpho-physiological and molecular response of plant to HS, and a few possible management strategies.

9-cis-epoxycarotenoid dioxygenase 1 confers heat stress tolerance in rice seedling plants

High temperature is one of the main constraints affecting plant growth and development. It has been reported that abscisic acid (ABA) synthesis gene 9-cis-epoxycarotenoid dioxygenase (NCED) positively regulates plant resistance to salt, cold, and drought stresses. However, little is known about the function of the NCED gene in heat tolerance of rice. Here, we found that OsNCED1 was a heat stress inducible gene. Rice seedlings overexpressing OsNCED1 showed enhanced heat tolerance with more abundant ABA content, whereas the knockout mutant osnced1 accumulated less ABA and showed more sensitive to heat stress. Under heat stress, increased expression of OsNCED1 could reduce membrane damage and reactive oxygen species (ROS) level of plants, and elevate the activity of antioxidant enzymes. Moreover, real time-quantitative PCR (RT-qPCR) analysis showed that overexpression of OsNCED1 significantly activated the expression of genes involved in antioxidant enzymes, ABA signaling pathway, heat response, and defense. Together, our results indicate that OsNCED1 positively regulates heat tolerance of rice seedling by raising endogenous ABA contents, which leads to the improved antioxidant capacity and activated expression of heat and ABA related genes.

Cold Stress Response Mechanisms in Anther Development

Unlike animals that can escape threats, plants must endure and adapt to biotic and abiotic stresses in their surroundings. One such condition, cold stress, impairs the normal growth and development of plants, in which most phases of reproductive development are particularly susceptible to external low temperature. Exposed to uncomfortably low temperature at the reproductive stage, meiosis, tapetal programmed cell death (PCD), pollen viability, and fertilization are disrupted, resulting in plant sterility. Of them, cold-induced tapetal dysfunction is the main cause of pollen sterility by blocking nutrition supplements for microspore development and altering their timely PCD. Further evidence has indicated that the homeostatic imbalances of hormones, including abscisic acid (ABA) and gibberellic acid (GA), and sugars have occurred in the cold-treated anthers. Among them, cold stress gives rise to the accumulation of ABA and the decrease of active GA in anthers to affect tapetal development and represses the transport of sugar to microspores. Therefore, plants have evolved lots of mechanisms to alleviate the damage of external cold stress to reproductive development by mainly regulating phytohormone levels and sugar metabolism. Herein, we discuss the physiological and metabolic effects of low temperature on male reproductive development and the underlying mechanisms from the perspective of molecular biology. A deep understanding of cold stress response mechanisms in anther development will provide noteworthy references for cold-tolerant crop breeding and crop production under cold stress.

Increased ATPase activity promotes heat-resistance, high-yield, and high-quality traits in rice by improving energy status

Heat stress during the reproductive stage results in major losses in yield and quality, which might be mainly caused by an energy imbalance. However, how energy status affected heat response, yield and quality remains unclear. No relationships were observed among the heat resistance, yield, and quality of the forty-nine early rice cultivars under normal temperature conditions. However, two cultivars, Zhuliangyou30 (ZLY30) and Luliangyou35 (LLY35), differing in heat resistance, yield, and quality were detected. The yield was higher and the chalkiness degree was lower in ZLY30 than in LLY35. Decreases in yields and increases in the chalkiness degree with temperatures were more pronounced in LLY35 than in ZLY30. The accumulation and allocation (ratio of the panicle to the whole plant) of dry matter weight and non-structural carbohydrates were higher in ZLY30 than in LLY35 across all sowing times and temperatures. The accumulation and allocation of dry matter weight and non-structural carbohydrates in panicles were higher in ZLY30 than in LLY35. Similar patterns were observed in the relative expression levels of sucrose unloading related genes SUT1 and SUT2 in grains. The ATP content was higher in the grains of LLY35 than in ZLY30, whereas the ATPase activity, which determined the energy status, was significantly lower in the former than in the latter. Thus, increased ATPase activity, which improved the energy status of rice, was the factor mediating the balance among heat-resistance, high-yield, and high-quality traits in rice.

Abscisic Acid Improves Rice Thermo-Tolerance by Affecting Trehalose Metabolism

Heat stress that occurs during the flowering stage severely decreases the rice (Oryza sativa L.) seed-setting rate. This damage can be reversed by abscisic acid (ABA), through effects on reactive oxygen species, carbohydrate metabolism, and heat shock proteins, but the exact role of trehalose and ATP in this process remains unclear. Two rice genotypes, namely, Zhefu802 (heat-resistant plant, a recurrent parent) and its near-isogenic line (faded green leaf, Fgl, heat-sensitive plant), were subjected to 38 °C heat stress after being sprayed with ABA or its biosynthetic inhibitor, fluridone (Flu), at the flowering stage. The results showed that exogenous ABA significantly increased the seed-setting rate of rice under heat stress, by 14.31 and 22.40% in Zhefu802 and Fgl, respectively, when compared with the H₂O treatment. Similarly, exogenous ABA increased trehalose content, key enzyme activities of trehalose metabolism, ATP content, and F1Fo-ATPase activity. Importantly, the opposite results were observed in plants treated with Flu. Therefore, ABA may improve rice thermo-tolerance by affecting trehalose metabolism and ATP consumption.

Overcoming Reproductive Compromise Under Heat Stress in Wheat: Physiological and Genetic Regulation, and Breeding Strategy

The reproductive compromise under heat stress is a major obstacle to achieve high grain yield and quality in wheat worldwide. Securing reproductive success is the key solution to sustain wheat productivity by understanding the physiological mechanism and molecular basis in conferring heat tolerance and utilizing the candidate gene resources for breeding. In this study, we examined the performance on both carbon supply source (as leaf photosynthetic rate) and carbon sink intake (as grain yields and quality) in wheat under heat stress varying with timing, duration, and intensity, and we further surveyed physiological processes from source to sink and the associated genetic basis in regulating reproductive thermotolerance; in addition, we summarized the quantitative trait loci (QTLs) and genes identified for heat stress tolerance associated with reproductive stages. Discovery of novel genes for thermotolerance is made more efficient via the combination of transcriptomics, proteomics, metabolomics, and phenomics. Gene editing of specific genes for novel varieties governing heat tolerance is also discussed.

Thermo-Priming Mediated Cellular Networks for Abiotic Stress Management in Plants

Plants can adapt to different environmental conditions and can survive even under very harsh conditions. They have developed elaborate networks of receptors and signaling components, which modulate their biochemistry and physiology by regulating the genetic information. Plants also have the abilities to transmit information between their different parts to ensure a holistic response to any adverse environmental challenge. One such phenomenon that has received greater attention in recent years is called stress priming. Any milder exposure to stress is used by plants to prime themselves by modifying various cellular and molecular parameters. These changes seem to stay as memory and prepare the plants to better tolerate subsequent exposure to severe stress. In this review, we have discussed the various ways in which plants can be primed and illustrate the biochemical and molecular changes, including chromatin modification leading to stress memory, with major focus on thermo-priming. Alteration in various hormones and their subsequent role during and after priming under various stress conditions imposed by changing climate conditions are also discussed.

Comparative physiological and transcriptomic analysis of sesame cultivars with different tolerance responses to heat stress

High temperature is the main factor affecting plant growth and can cause plant growth inhibition and yield reduction. Here, seedlings of two contrasting sesame varieties, i.e., Zheng Taizhi 3 (heat-tolerant) and SP19 (heat-sensitive), were treated at 43 °C for 10 days. The results showed that the relative electrical conductivity, hydrogen peroxide levels, and superoxide anion radical levels of both varieties increased significantly under high temperature stress. Additionally, dry matter accumulation and chlorophyll content decreased significantly, and the activities of peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) increased. However, under HT stress, the content of reactive oxygen species in Zheng Taizhi 3 was lower than that in SP19, and the activities of SOD, CAT, and POD as well as the chlorophyll content in Zheng Taizhi 3 were higher than those in SP19. Comparative transcriptome analysis identified 6736 differentially expressed genes (DEGs); 5526 DEGs (2878 up and 2648 down) were identified in Zheng Taizhi 3, and 5186 DEGs (2695 up and 2491 down) were identified in SP19, with 3976 overlapping DEGs. These DEGs included stress tolerance-related heat-shock proteins, as well as genes related to carbohydrate and energy metabolism, signal transduction, endoplasmic reticulum protein processing, amino acid metabolism, and secondary metabolism. Overall, our results showed that the heat tolerance of Zheng Taizhi 3 was attributed to a stronger antioxidant defense system, enabling the variety to avoid oxidative damage compared with the heat-sensitive SP19. Moreover, some specifically expressed and high-abundance genes in Zheng Taizhi 3 were involved in regulatory mechanisms related to heat tolerance, including plant hormone signal transduction and heat shock protein regulation, thereby enhancing heat tolerance. The study contributes to a deeper understanding of the underlying complex molecular mechanisms involved in the responses of sesame seedlings to heat stress and provides a potential strategy for heat-resistant new varieties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01195-3.

Low Salicylic Acid Level Improves Pollen Development Under Long-Term Mild Heat Conditions in Tomato

Exposure to high temperatures leads to failure in pollen development, which may have significant implications for food security with ongoing climate change. We hypothesized that the stress response-associated hormone salicylic acid (SA) affects pollen tolerance to long-term mild heat (LTMH) (≥14 days exposure to day-/nighttime temperature of 30-34/24-28°C, depending on the genotype), either positively, by inducing acclimation, or negatively, by reducing investment in reproductive development. Here, we investigated these hypotheses assessing the pollen thermotolerance of a 35S:nahG tomato line, which has low SA levels. We found that reducing the SA level resulted in increased pollen viability of plants grown in LTMH and further characterized this line by transcriptome, carbohydrate, and hormone analyses. Low expression of JAZ genes in 35S:nahG and LTMH hypersensitivity of low-jasmonic acid (JA) genotypes together suggest that the increased pollen thermotolerance in the low-SA line involves enhanced JA signal in developing anthers in LTMH. These findings have potential application in the development of more thermotolerant crops.

Metabolomic profiling of brassinolide and abscisic acid in response to high-temperature stress

Hormone treatment enhanced the content of osmotic substances under high-temperature conditions. The effect of ABA and BR treated separately is better than treated together. To determine the effect of abscisic acid (ABA), brassinolide (BR) and ABA + BR on grape quality under high-temperature stress, various metabolites were analyzed. Compared with the control (CK), DL-tryptophan, D-raffinose, geniposidic acid, dodecanedioic acid and polyphenols were found to be higher after ABA treatment. After BR treatment, amino acids and poricoic acid B were higher than in CK. And carbohydrates and amino acids were up-regulated after ABA + BR treatment. BR and ABA + BR treatment also induced higher endogenous ABA and epibrassinolide contents. In addition, treated grape had higher soluble solid concentrations and soluble sugar content, and delayed the degradation of middle lamella and microfibrils. Antioxidant and heat shock-related genes were examined, which significantly increased in treated grape. The finding of this study suggested that ABA, BR and ABA + BR are very useful for alleviating high-temperature damage by increasing the accumulation of osmotic adjustment substances, and endogenous hormones content.

Reproductive resilience: putting pollen grains in two baskets

To ensure reproductive success, flowering plants produce an excess of pollen to fertilize a limited number of ovules. Pollen grains mature into two distinct subpopulations - those that display high metabolic activity and elevated reactive oxygen species (ROS) levels immediately after hydration (high-ROS/active), and those that maintain an extended period of dormancy with low metabolic activity (low-ROS/inactive/arrested/dormant). We propose that the dormant pollen serves as a backup to provide a second chance for successful fertilization when the 'first wave' of pollen encounters an unpredictable growth condition such as heat stress. This model provides a framework for considering the role of dormancy in reproductive stress tolerance as well as strategies for mitigating pollen thermovulnerability to daytime and night-time warming that is associated with global climate change.

Response and tolerance mechanism of food crops under high temperature stress: a review

High temperature stress events are critical factors inhibiting crop yield. Meanwhile, world population is growing very rapidly and will be reached up to 9 billion by 2050. To feed increasing world population, it is challenging task to increase about 70% global food productions. Food crops have significant contribution toward global food demand and food security. However, consequences from increasing heat stress events are demolishing their abilities to survive and sustain yield when subjected to extreme high temperature stress. Therefore, there is dire need to better understand response and tolerance mechanism of food crops following exposure to heat stress. Here, we aimed to provide recent update on impact of high temperature stress on crop yield of food crops, pollination, pollinators, and novel strategies for improving tolerance of food crop under high temperature stress. Importantly, development of heat-resistant transgenic food crops can grant food security through transformation of superior genes into current germplasm, which are associated with various signaling pathways as well as epigenetic regulation in response to extreme high temperature stress.

Functions of Redox Signaling in Pollen Development and Stress Response

Cellular redox homeostasis is crucial for normal plant growth and development. Each developmental stage of plants has a specific redox mode and is maintained by various environmental cues, oxidants, and antioxidants. Reactive oxygen species (ROS) and reactive nitrogen species are the chief oxidants in plant cells and participate in cell signal transduction and redox balance. The production and removal of oxidants are in a dynamic balance, which is necessary for plant growth. Especially during reproductive development, pollen development depends on ROS-mediated tapetal programmed cell death to provide nutrients and other essential substances. The deviation of the redox state in any period will lead to microspore abortion and pollen sterility. Meanwhile, pollens are highly sensitive to environmental stress, in particular to cell oxidative burst due to its peculiar structure and function. In this regard, plants have evolved a series of complex mechanisms to deal with redox imbalance and oxidative stress damage. This review summarizes the functions of the main redox components in different stages of pollen development, and highlights various redox protection mechanisms of pollen in response to environmental stimuli. In continuation, we also discuss the potential applications of plant growth regulators and antioxidants for improving pollen vigor and fertility in sustaining better agriculture practices.

Climate change regulated abiotic stress mechanisms in plants: a comprehensive review

Global climate change is identified as a major threat to survival of natural ecosystems. Climate change is a dynamic, multifaceted system of alterations in environmental conditions that affect abiotic and biotic components of the world. It results in alteration in environmental conditions such as heat waves, intensity of rainfall, CO₂ concentration and temperature that lead to rise in new pests, weeds and pathogens. Climate change is one of the major constraints limiting plant growth and development worldwide. It impairs growth, disturbs photosynthesis, and reduces physiological responses in plants. The variations in global climate have gained the attention of researchers worldwide, as these changes negatively affect the agriculture by reducing crop productivity and food security. With this background, this review focuses on the effects of elevated atmospheric CO₂ concentration, temperature, drought and salinity on the morphology, physiology and biochemistry of plants. Furthermore, this paper outlines an overview on the reactive oxygen species (ROS) production and their impact on the biochemical and molecular status of plants with increased climatic variations. Also additionally, different tolerance strategies adopted by plants to combat environmental adversities have been discussed.

Integrated Isoform Sequencing and Dynamic Transcriptome Analysis Reveals Diverse Transcripts Responsible for Low Temperature Stress at Anther Meiosis Stage in Rice

Low temperatures stress is one of the important factors limiting rice yield, especially during rice anther development, and can cause pollen sterility and decrease grain yield. In our study, low-temperature stress decreased pollen viability and spikelet fertility by affecting the sugar, nitrogen and amino acid contents of anthers. We performed RNA-seq and ISO-seq experiments to study the genome-wide transcript expression profiles in low-temperature anthers. A total of 4,859 differentially expressed transcripts were detected between the low-temperature and control groups. Gene ontology enrichment analysis revealed significant terms related to cold tolerance. Hexokinase and glutamate decarboxylase participating in starch and sucrose metabolism may play important roles in the response to cold stress. Using weighted gene co-expression network analysis, nine hub transcripts were found that could improve cold tolerance throughout the meiosis period of rice: Os02t0219000-01 (interferon-related developmental regulator protein), Os01t0218350-00 (tetratricopeptide repeat-containing thioredoxin), Os08t0197700-00 (luminal-binding protein 5), Os11t0200000-01 (histone deacetylase 19), Os03t0758700-01 (WD40 repeat domain-containing protein), Os06t0220500-01 (7-deoxyloganetin glucosyltransferase), Pacbio.T01382 (sucrose synthase 1), Os01t0172400-01 (phospholipase D alpha 1), and Os01t0261200-01 (NAC domain-containing protein 74). In the PPI network, the protein minichromosome maintenance 4 (MCM4) may play an important role in DNA replication induced by cold stress.

Comparative Molecular and Metabolic Profiling of Two Contrasting Wheat Cultivars under Drought Stress

Drought is one of the most important threats to plants and agriculture; therefore, understanding of the mechanisms of drought tolerance is crucial for breeding of new tolerant varieties. Here, we assessed the effects of a long-term water deficit stress simulated on a precision phenotyping system on some morphological criteria and metabolite traits, as well as the expression of drought associated transcriptional factors of two contrasting drought-responsive African wheat cultivars, Condor and Wadielniel. The current study showed that under drought stress Wadielniel exhibits significant higher tillering and height compared to Condor. Further, we used gas chromatography and ultra-high performance liquid chromatography mass-spectrometry to identify compounds that change between the two cultivars upon drought. Partial least square discriminant analysis (PLS-DA) revealed that 50 metabolites with a possible role in drought stress regulation were significantly changed in both cultivars under water deficit stress. These metabolites included several amino acids, most notably proline, some organic acids, and lipid classes PC 36:3 and TAG 56:9, which were significantly altered under drought stress. Here, the results discussed in the context of understanding the mechanisms involved in the drought response of wheat cultivars, as the phenotype parameters, metabolite content and expression of drought associated transcriptional factors could also be used for potential crop improvement under drought stress.

Physiological and Transcriptomic Analyses Reveal Exogenous Trehalose Is Involved in the Responses of Wheat Roots to High Temperature Stress

High temperature stress seriously limits the yield and quality of wheat. Trehalose, a non-reducing disaccharide, has been shown involved in regulating plant responses to a variety of environmental stresses. This study aimed to explore the molecular regulatory network of exogenous trehalose to improve wheat heat tolerance through RNA-sequencing technology and physiological determination. The physiological data and RNA-seq showed that trehalose reduced malondialdehyde content and relative conductivity in wheat roots, and affecting the phenylpropane biosynthesis, starch and sucrose metabolism, glutathione metabolism, and other pathways. Our results showed that exogenous trehalose alleviates the oxidative damage caused by high temperature, coordinating the effect of wheat on heat stress by re-encoding the overall gene expression, but two wheat varieties showed different responses to high temperature stress after trehalose pretreatment. This study preliminarily revealed the effect of trehalose on gene expression regulation of wheat roots under high temperature stress, which provided a reference for the study of trehalose.

Genome-wide identification of ABA receptor PYL/RCAR gene family and their response to cold stress in Medicago sativa L

Abscisic acid (ABA) is an important phytohormone involved in plant growth, plant development, and the protection of plants against abiotic stresses. PYL/RCAR (pyrabactin resistance/pyr1-like/regulatory components of ABA receptor) is the receptor protein of ABA and the core component of the ABA signal transduction network. The PYL gene family has been identified and analyzed in many species, however, there is no report about the research on the whole genome-wide identification of the alfalfa (Medicago sativa L.) PYL gene family. Therefore, to explore the function of alfalfa PYL genes, 39 MsPYL genes were identified by analyzing the recently published genome of alfalfa. Using bioinformatics methods, we systematically analyzed the chromosome location, protein physicochemical properties, evolutionary relationship, conserved motifs, and response to low-temperature stress of the MsPYL family of alfalfa. The results showed that 39 alfalfa MsPYL genes were distributed on 24 chromosomes, and the analysis of gene duplication events showed that fragment duplication was predominant duplication in alfalfa MsPYL family gene expansion. The phylogenetic tree of MsPYL protein of alfalfa and the phylogenetic tree of PYL genes of 3 species show that the MsPYL gene family can be divided into 3 subfamilies, and the structures of the same subfamilies are relatively similar. The 39 MsPYL gene family members of alfalfa contain 10 Motifs. Motif1, Motif2, Motif3, and Motif5 are the conserved motifs shared by these genes; cis-regulatory elements in promoter regions indicate that regulatory elements related to transcription, cell cycle, development, hormone, and stress response are abundantly present in the MsPYL promoter sequences; Real-time fluorescence quantitative PCR analysis showed that the expression of MsPYL genes can be induced by low-temperature treatment. This study provides a reference for further exploring the structural and functional characterization of the alfalfa PYL gene family.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01066-3.

Contrasting anther glucose-6-phosphate dehydrogenase activities between two bean varieties suggest an important role in reproductive heat tolerance

Common beans (Phaseolus vulgaris) are highly sensitive to elevated temperatures, and rising global temperatures threaten bean production. Plants at the reproductive stage are especially susceptible to heat stress due to damage to male (anthers) and female (ovary) reproductive tissues, with anthers being more sensitive to heat. Heat damage promotes early tapetal cell degradation, and in beans this was shown to cause male infertility. In this study, we focus on understanding how changes in leaf carbon export in response to elevated temperature stress contribute to heat-induced infertility. We hypothesize that anther glucose-6-phosphate dehydrogenase (G6PDH) activity plays an important role at elevated temperature and promotes thermotolerance. To test this hypothesis, we compared heat-tolerant and susceptible common bean genotypes using a combination of phenotypic, biochemical, and physiological approaches. Our results identified changes in leaf sucrose export, anther sugar accumulation and G6PDH activity and anther H₂ O₂ levels and antioxidant-related enzymes between genotypes at elevated temperature. Further, anther respiration rate was found to be lower at high temperature in both bean varieties. Overall, our results support the hypothesis that enhanced male reproductive heat tolerance involves changes in the anther oxidative pentose phosphate pathway, which supplies reductants to critical H₂ O₂ scavenging enzymes.

Quantitative proteomic analyses reveal that energy metabolism and protein biosynthesis reinitiation are responsible for the initiation of bolting induced by high temperature in lettuce (Lactuca sativa L.)

BACKGROUND

Lettuce (Lactuca sativa L.), one of the most economically important leaf vegetables, exhibits early bolting under high-temperature conditions. Early bolting leads to loss of commodity value and edibility, leading to considerable loss and waste of resources. However, the initiation and molecular mechanism underlying early bolting induced by high temperature remain largely elusive.

RESULTS

In order to better understand this phenomenon, we defined the lettuce bolting starting period, and the high temperature (33 °C) and controlled temperature (20 °C) induced bolting starting phase of proteomics is analyzed, based on the iTRAQ-based proteomics, phenotypic measurement, and biological validation by RT-qPCR. Morphological and microscopic observation showed that the initiation of bolting occurred 8 days after high-temperature treatment. Fructose accumulated rapidly after high-temperature treatment. During initiation of bolting, of the 3305 identified proteins, a total of 93 proteins exhibited differential abundances, 38 of which were upregulated and 55 downregulated. Approximately 38% of the proteins were involved in metabolic pathways and were clustered mainly in energy metabolism and protein synthesis. Furthermore, some proteins involved in sugar synthesis were differentially expressed and were also associated with energy production.

CONCLUSIONS

This report is the first to report on the metabolic changes involved in the initiation of bolting in lettuce. Our study suggested that energy metabolism and ribosomal proteins are pivotal components during initiation of bolting. This study could provide a potential regulatory mechanism for the initiation of early bolting by high temperature, which could have applications in the manipulation of lettuce for breeding.

Screening and identification of genes affecting grain quality and spikelet fertility during high-temperature treatment in grain filling stage of rice

BACKGROUND

Recent temperature increases due to rapid climate change have negatively affected rice yield and grain quality. Particularly, high temperatures during right after the flowering stage reduce spikelet fertility, while interfering with sugar energy transport, and cause severe damage to grain quality by forming chalkiness grains. The effect of high-temperature on spikelet fertility and grain quality during grain filling stage was evaluated using a double haploid line derived from another culture of F1 by crossing Cheongcheong and Nagdong cultivars. Quantitative trait locus (QTL) mapping identifies candidate genes significantly associated with spikelet fertility and grain quality at high temperatures.

RESULTS

Our analysis screened OsSFq3 that contributes to spikelet fertility and grain quality at high-temperature. OsSFq3 was fine-mapped in the region RM15749-RM15689 on chromosome 3, wherein four candidate genes related to the synthesis and decomposition of amylose, a starch component, were predicted. Four major candidate genes, including OsSFq3, and 10 different genes involved in the synthesis and decomposition of amylose and amylopectin, which are starch constituents, together with relative expression levels were analyzed. OsSFq3 was highly expressed during the initial stage of high-temperature treatment. It exhibited high homology with FLOURY ENDOSPERM 6 in Gramineae plants and is therefore expected to function similarly.

CONCLUSION

The QTL, major candidate genes, and OsSFq3 identified herein could be effectively used in breeding rice varieties to improve grain quality, while tolerating high temperatures, to cope with climate changes. Furthermore, linked markers can aid in marker-assisted selection of high-quality and -yield rice varieties tolerant to high temperatures.