Sugar metabolism during pre- and post-fertilization events in plants under high temperature stress

A systematic review on the implications of concurrent heat and drought stress in modulating floral development in plants

The continuous change in climate, along with irregular rainfall patterns, poses a significant threat to sustainable agricultural productivity worldwide. Both high temperatures and drought stress are key factors limiting crop growth, and with global climate change, the occurrence of combined heat and drought stress is expected to rise. This will further exacerbate the vulnerability of agricultural yield. Simultaneous heat and drought stress is prevalent in field conditions, and while extensive research has been done on the individual effects of heat and drought stress on plants, little is known about the molecular mechanisms underlying plant acclimation to a combination of these stressors. The reproductive stage, especially the flowering phase, has been identified as the most sensitive to both heat and drought stress, leading to sterility in plants. However, our understanding of the combined stress response in commonly used crop plants is still limited. Hence, it is crucial to study and comprehend the effects and interactions between high temperatures and drought stress during the reproductive stages of crops. This review delves into the morpho-physiological changes in reproductive organs of various plant species under combined heat and drought stress and also details the molecular regulation of the mechanism of combined stress tolerance in plants. Notably, the article incorporates expression analyses of candidate genes in rice flowers, emphasizing the utilization of modern biotechnological methods to enhance stress tolerance in plants. Overall, the review provides a comprehensive insight into the regulation of floral development in plants following concurrent heat and drought stress.

Extreme heat exposure of host plants indirectly reduces solitary bee fecundity and survival

Extreme heat poses a major threat to plants and pollinators, yet the indirect consequences of heat stress are not well understood, particularly for native solitary bees. To determine how brief exposure of extreme heat to flowering plants affects bee behaviour, fecundity, development and survival we conducted a no-choice field cage experiment in which Osmia lignaria were provided blueberry (Vaccinium corymbosum), phacelia (Phacelia tanacetifolia) and white clover (Trifolium repens) that had been previously exposed to either extreme heat (37.5°C) or normal temperatures (25°C) for 4 h during early bloom. Despite a similar number of open flowers and floral visitation frequency between the two treatments, female bees provided with heat-stressed plants laid approximately 70% fewer eggs than females provided with non-stressed plants. Their progeny received similar quantities of pollen provisions between the two treatments, yet larvae consuming pollen from heat-stressed plants had significantly lower survival as larvae and adults. We also observed trends for delayed emergence and reduced adult longevity when larvae consumed heat-stressed pollen. This study is the first to document how short, field-realistic bursts of extreme heat exposure to flowering host plants can indirectly affect bee pollinators and their offspring, with important implications for crop pollination and native bee populations.

Genome-wide association study for seedling heat tolerance under two temperature conditions in bread wheat (Triticum aestivum L.)

BACKGROUND

As the greenhouse effect intensifies, global temperatures are steadily increasing, posing a challenge to bread wheat (Triticum aestivum L.) production. It is imperative to comprehend the mechanism of high temperature tolerance in wheat and implement breeding programs to identify and develop heat-tolerant wheat germplasm and cultivars.

RESULTS

To identify quantitative trait loci (QTL) related to heat stress tolerance (HST) at seedling stage in wheat, a panel of 253 wheat accessions which were re-sequenced used to conduct genome-wide association studies (GWAS) using the factored spectrally transformed linear mixed models (FaST-LMM). For most accessions, the growth of seedlings was found to be inhibited under heat stress. Analysis of the phenotypic data revealed that under heat stress conditions, the main root length, total root length, and shoot length of seedlings decreased by 47.46%, 49.29%, and 15.19%, respectively, compared to those in normal conditions. However, 17 varieties were identified as heat stress tolerant germplasm. Through GWAS analysis, a total of 115 QTLs were detected under both heat stress and normal conditions. Furthermore, 15 stable QTL-clusters associated with heat response were identified. By combining gene expression, haplotype analysis, and gene annotation information within the physical intervals of the 15 QTL-clusters, two novel candidate genes, TraesCS4B03G0152700/TaWRKY74-B and TraesCS4B03G0501400/TaSnRK3.15-B, were responsive to temperature and identified as potential regulators of HST in wheat at the seedling stage.

CONCLUSIONS

This study conducted a detailed genetic analysis and successfully identified two genes potentially associated with HST in wheat at the seedling stage, laying a foundation to further dissect the regulatory mechanism underlying HST in wheat under high temperature conditions. Our finding could serve as genomic landmarks for wheat breeding aimed at improving adaptation to heat stress in the face of climate change.

Physiological and Transcriptome Analyses Reveal the Protective Effect of Exogenous Trehalose in Response to Heat Stress in Tea Plant (Camellia sinensis)

It is well known that application of exogenous trehalose can enhance the heat resistance of plants. To investigate the underlying molecular mechanisms by which exogenous trehalose induces heat resistance in C. sinensis, a combination of physiological and transcriptome analyses was conducted. The findings revealed a significant increase in the activity of superoxide dismutase (SOD) and peroxidase (POD) upon treatment with 5.0 mM trehalose at different time points. Moreover, the contents of proline (PRO), endogenous trehalose, and soluble sugar exhibited a significant increase, while malondialdehyde (MDA) content decreased following treatment with 5.0 mM trehalose under 24 h high-temperature stress (38 °C/29 °C, 12 h/12 h). RNA-seq analysis demonstrated that the differentially expressed genes (DEGs) were significantly enriched in the MAPK pathway, plant hormone signal transduction, phenylpropanoid biosynthesis, flavone and flavonol biosynthesis, flavonoid biosynthesis, and the galactose metabolism pathway. The capability to scavenge free radicals was enhanced, and the expression of a heat shock factor gene (HSFB2B) and two heat shock protein genes (HSP18.1 and HSP26.5) were upregulated in the tea plant. Consequently, it was concluded that exogenous trehalose contributes to alleviating heat stress in C. sinensis. Furthermore, it regulates the expression of genes involved in diverse pathways crucial for C. sinensis under heat-stress conditions. These findings provide novel insights into the molecular mechanisms underlying the alleviation of heat stress in C. sinensis with trehalose.

Salicylic acid-functionalised chitosan nanoparticles restore impaired sucrose metabolism in the developing anther of cotton (Gossypium hirsutum) under heat stress

Nanotechnology provides tremendous potential in agriculture, mitigating climate change impact and improving abiotic stress management strategy. Chitosan nanoparticles (NCS) were synthesised using the ion gelation method and characterised for size (75.5nm in particle size analyser), shape (spherical under scanning electron microscopy) and stability (132.2mV zeta potential). Further, salicylic acid was incorporated into NCS to craft salicylic acid-functionalised chitosan nanoparticles (SA-NCS) and illustrated for size (517nm), shape (spherical) and stability (197.1mV). The influence of the exogenous application of SA-NCS (0.08%) was studied at the reproductive stage of three genotypes of cotton (Gossypium hirsutum ): (1) heat-tolerant Solar-651 BGII; (2) moderately heat-tolerant Solar-701 BGII; and (3) heat-susceptible Solar-805 BGII, exposed to different temperature regimes: (1) H1 (optimal), 32/20±2°C; (2) H2 (sub-optimal), 38/24±2°C; H3 (supra-optimal), 45/30±2°C. Heat stress significantly reduces carbon-fixing Rubisco, enzymes related to sucrose metabolism and pollen tube length. Considering three genotypes and reproductive stages (sepal and anther tissues), activities of Rubisco (sepals), invertase (sepals), sucrose phosphate synthase (anthers), sucrose content (sepals) and pollen tube length were elevated under high-temperature regimes, signifying better source to sink transposition of sucrose influenced by SA-NCS. The study provides new insights into SA-NCS to improve source-sink imbalance and restore sucrose metabolism for better growth of reproductive structure under heat stress in cotton.

Transcriptome analysis of ovules offers early developmental clues after fertilization in Cicer arietinum L

Chickpea (Cicer arietinum L.) seeds are valued for their nutritional scores and limited information on the molecular mechanisms of chickpea fertilization and seed development is available. In the current work, comparative transcriptome analysis was performed on two different stages of chickpea ovules (pre- and post-fertilization) to identify key regulatory transcripts. Two-staged transcriptome sequencing was generated and over 208 million reads were mapped to quantify transcript abundance during fertilization events. Mapping to the reference genome showed that the majority (92.88%) of high-quality Illumina reads were aligned to the chickpea genome. Reference-guided genome and transcriptome assembly yielded a total of 28,783 genes. Of these, 3399 genes were differentially expressed after the fertilization event. These involve upregulated genes including a protease-like secreted in CO(2) response (LOC101500970), amino acid permease 4-like (LOC101506539), and downregulated genes MYB-related protein 305-like (LOC101493897), receptor like protein 29 (LOC101491695). WGCNA analysis and pairwise comparison of datasets, successfully constructed four co-expression modules. Transcription factor families including bHLH, MYB, MYB-related, C2H2 zinc finger, ERF, WRKY and NAC transcription factor were also found to be activated after fertilization. Activation of these genes and transcription factors results in the accumulation of carbohydrates and proteins by enhancing their trafficking and biosynthesis. Total 17 differentially expressed genes, were randomly selected for qRT-PCR for validation of transcriptome analysis and showed statistically significant correlations with the transcriptome data. Our findings provide insights into the regulatory mechanisms underlying changes in fertilized chickpea ovules. This work may come closer to a comprehensive understanding of the mechanisms that initiate developmental events in chickpea seeds after fertilization.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03599-8.

The biochar-based nanocomposites improve seedling emergence and growth of dill by changing phytohormones and sugar signaling under salinity

Biochar-based nanocomposites (BNCs) with a high level of sodium sorption capacity may improve salinity tolerance and seedling establishment of dill. Thus, a pot experiment was conducted to evaluate the effects of solid biochar (30 g solid biochar kg^-1 soil) and biochar-based nanocomposites of iron (BNC-FeO) and zinc (BNC-ZnO) in individual (30 g BNC kg^-1 soil) and a combined form (15 g BNC-FeO + 15 g BNC-ZnO kg^-1 soil) on dill seedling growth in different levels of salt stress (non-saline, 6 and 12 dSm^-1). Salinity caused a decrease in emergence percentage and emergence rate of seedlings. Increasing salinity of soil up to 12 dSm^-1 decreased the biomass of dill seedlings by about 77%. Application of biochar and particularly BNCs increased the content of potassium, calcium, magnesium, iron, and zinc, reducing and non-reducing sugars, total sugars, invertase and sucrose synthase activities, leaf water content, gibberellic acid, and indole-3-acetic acid in dill plants, leading to an improvement in seedling growth (shoot length, root length, and dry weight) under saline conditions. Sodium content was noticeably decreased by BNC treatments (9-21%), which reduced mean emergence rate and stress phytohormones such as abscisic acid (31-43%), jasmonic acid (21-42%), and salicylic acid (16-23%). Therefore, BNCs especially in combined form can potentially improve emergence and growth of dill seedlings under salt stress, through reducing sodium content and endogenous stress hormones, and enhancing sugars and growth promoting hormones.

Parthenocarpic tomato mutants, iaa9-3 and iaa9-5, show plant adaptability and fruiting ability under heat-stress conditions

Fruit set is one of the main problems that arise in tomato plants under heat-stress conditions, which disrupt pollen development, resulting in decreased pollen fertility. Parthenocarpic tomatoes can be used to increase plant productivity during failure of the fertilisation process under heat-stress conditions. The aim of this study were to identify the plant adaptability and fruiting capability of ?iaa9-3 and iaa9-5 tomato mutants under heat-stress conditions. The iaa9-3 and iaa9-5 and wild-type Micro-Tom (WT-MT) plants were cultivated under two temperature conditions: normal and heat-stress conditions during plant growth. The results showed that under the heat-stress condition, iaa9-3 and iaa9-5 showed delayed flowering time, increased number of flowers, and increased fruit set and produced normal-sized fruit. However, WT-MT cannot produce fruits under heat stress. The mutants can grow under heat-stress conditions, as indicated by the lower electrolyte leakage and H₂O₂ concentration and higher antioxidant activities compared with WT-MT under heat-stress conditions. These results suggest that iaa9-3 and iaa9-5 can be valuable genetic resources for the development of tomatoes in high-temperature environmental conditions.

Hydrogen Peroxide and GA3 Levels Regulate the High Night Temperature Response in Pistils of Wheat (Triticum aestivum L.)

High night temperature (HNT) impairs crop productivity through the reproductive failure of gametes (pollen and pistil). Though female gametophyte (pistil) is an equal partner in the seed-set, the knowledge of the antioxidant system(s) and hormonal control of HNT tolerance or susceptibility of pistils is limited and lacking. The objectives of this study were to determine the antioxidant mechanism for homeostatic control of free radicals, and the involvement of abscisic acid (ABA) and gibberellic acid (GA₃) in HNT stress protection in the wheat pistils of contrasting wheat genotypes. We hypothesized that HNT tolerance is attributed to the homeostatic control of reactive oxygen species (ROS) and hormonal readjustment in pistils of the tolerant genotype. The ears of two contrasting wheat genotypes-HD 2329 (susceptible) and Raj 3765 (tolerant) were subjected to two HNTs (+5 °C and +8 °C) over ambient, in the absence and presence of dimethylthiourea (DMTU), a chemical trap of hydrogen peroxide (H₂O₂). Results showed that HNTs significantly increased ROS in pistils of susceptible genotype HD 2329 to a relatively greater extent compared to tolerant genotype Raj 3765. The response was similar in the presence or absence of DMTU, but the H₂O₂ values were lower in the presence of DMTU. The ROS levels were balanced by increased activity of peroxidase under HNT to a greater extent in the tolerant genotype. Cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPC) activity was inversely related to H₂O₂ production within a critical range in Raj 3765, indicating its modulation by H₂O₂ levels as no change was observed at the transcriptional level. The hormonal status showed increased ABA and decreased GA₃ contents with increasing temperature. Our study elucidates the role of H₂O₂ and GA₃ in stress tolerance of pistils of tolerant genotype where GAPC acts as a ROS sensor due to H₂O₂-mediated decrease in its activity.

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.

Identification of key gene networks controlling polysaccharide accumulation in different tissues of Polygonatum cyrtonema Hua by integrating metabolic phenotypes and gene expression profiles

Plant polysaccharides, a type of important bioactive compound, are involved in multiple plant defense mechanisms, and in particular polysaccharide-alleviated abiotic stress has been well studied. Polygonatum cyrtonema Hua (P. cyrtonema Hua) is a medicinal and edible perennial plant that is used in traditional Chinese medicine and is rich in polysaccharides. Previous studies suggested that sucrose might act as a precursor for polysaccharide biosynthesis. However, the role of sucrose metabolism and transport in mediating polysaccharide biosynthesis remains largely unknown in P. cyrtonema Hua. In this study, we investigated the contents of polysaccharides, sucrose, glucose, and fructose in the rhizome, stem, leaf, and flower tissues of P. cyrtonema Hua, and systemically identified the genes associated with the sucrose metabolism and transport and polysaccharide biosynthesis pathways. Our results showed that polysaccharides were mainly accumulated in rhizomes, leaves, and flowers. Besides, there was a positive correlation between sucrose and polysaccharide content, and a negative correlation between glucose and polysaccharide content in rhizome, stem, leaf, and flower tissues. Then, the transcriptomic analyses of different tissues were performed, and differentially expressed genes related to sucrose metabolism and transport, polysaccharide biosynthesis, and transcription factors were identified. The analyses of the gene expression patterns provided novel regulatory networks for the molecular basis of high accumulation of polysaccharides, especially in the rhizome tissue. Furthermore, our findings explored that polysaccharide accumulation was highly correlated with the expression levels of SUS, INV, SWEET, and PLST, which are mediated by bHLH, bZIP, ERF, ARF, C2H2, and other genes in different tissues of P. cyrtonema Hua. Herein, this study contributes to a comprehensive understanding of the transcriptional regulation of polysaccharide accumulation and provides information regarding valuable genes involved in the tolerance to abiotic stresses in P. cyrtonema Hua.

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.