Drought limits pollen tube growth rate by altering carbohydrate metabolism in cotton (Gossypium hirsutum) pistils

Metabolite-mediated adaptation of crops to drought and the acquisition of tolerance

Drought is one of the major and growing threats to agriculture productivity and food security. Metabolites are involved in the regulation of plant responses to various environmental stresses, including drought stress. The complex drought tolerance can be ascribed to several simple metabolic traits. These traits could then be used for detecting the genetic architecture of drought tolerance. Plant metabolomes show dynamic differences when drought occurs during different developmental stages or upon different levels of drought stress. Here, we reviewed the major and most recent findings regarding the metabolite-mediated plant drought response. Recent progress in the development of drought-tolerant agents is also discussed. We provide an updated schematic overview of metabolome-driven solutions for increasing crop drought tolerance and thereby addressing an impending agricultural challenge.

Exploring the relationship between pollen viability and inclusion in Paeonia lactiflora after cryopreservation

Pollen, as the male gametophyte, carries half of plant genetic information and is an important source of germplasm. The cryopreservation of pollen can not only preserve germplasm, but also solve the problem of time and space barrier in crossbreeding. So it is of great significance to explore the mechanism of pollen viability maintenance after cryopreservation. In this paper, 10 cultivars of Paeonia lactiflora with different fresh pollen viability that did not change after cryopreservation were taken as objects and the effects of pollen inclusions such as soluble sugar, starch, soluble protein, free amino acids, and proline were explored. The results showed that: (1) The contents of pollen inclusions in the fresh pollen of 10 cultivars were different. After cryopreservation, the contents of starch and free amino acids significantly decreased in 10 cultivars, and the soluble sugar, soluble protein, and proline varied with cultivars. (2) Correlation analysis showed that fresh pollen viability was significantly positively correlated with the soluble sugar (R-values of 0.630) and starch content (R-values of 0.694) in fresh pollen. But after cryopreservation pollen viability was only significantly positively correlated with the starch content (R-values of 0.725). These results suggest that the effects of pollen inclusions on pollen vitality are different before and after cryopreservation. The fresh pollen with higher soluble sugar and starch is more vital. But after cryopreservation, the pollen with high starch content has higher viability. The maintenance of stable pollen viability after cryopreservation appears to be related to starch content or starch metabolism, which requires further to study for a final determination.

Genome-wide genetic architecture for plant maturity and drought tolerance in diploid potatoes

Cultivated potato (Solanum tuberosum) is known to be highly susceptible to drought. With climate change and its frequent episodes of drought, potato growers will face increased challenges to achieving their yield goals. Currently, a high proportion of untapped potato germplasm remains within the diploid potato relatives, and the genetic architecture of the drought tolerance and maturity traits of diploid potatoes is still unknown. As such, a panel of 384 ethyl methanesulfonate-mutagenized diploid potato clones were evaluated for drought tolerance and plant maturity under field conditions. Genome-wide association studies (GWAS) were conducted to dissect the genetic architecture of the traits. The results obtained from the genetic structure analysis of the panel showed five main groups and seven subgroups. Using the Genome Association and Prediction Integrated Tool-mixed linear model GWAS statistical model, 34 and 17 significant quantitative trait nucleotides (QTNs) were found associated with maturity and drought traits, respectively. Chromosome 5 carried most of the QTNs, some of which were also detected by using the restricted two-stage multi-locus multi-allele-GWAS haploblock-based model, and two QTNs were found to be pleiotropic for both maturity and drought traits. Using the non-parametric U-test, one and three QTNs, with 5.13%-7.4% phenotypic variations explained, showed favorable allelic effects that increase the maturity and drought trait values. The quantitaive trait loci (QTLs)/QTNs associated with maturity and drought trait were found co-located in narrow (0.5-1 kb) genomic regions with 56 candidate genes playing roles in plant development and senescence and in abiotic stress responses. A total of 127 potato clones were found to be late maturing and tolerant to drought, while nine were early to moderate-late maturing and tolerant to drought. Taken together, the data show that the studied germplasm panel and the identified candidate genes are prime genetic resources for breeders and biologists in conventional breeding and targeted gene editing as climate adaptation tools.

Antioxidant defense in cotton under environmental stresses: Unraveling the crucial role of a universal defense regulator for enhanced cotton sustainability

Cotton (Gossypium spp.) is a globally significant crop that provides natural fibers for the textile industry and also an important oil and biopharmaceutical resources. However, the production of cotton faces substantial challenges due to various biotic and abiotic stress factors that can negatively impact cotton growth, yield, and fiber quality. This review offers a comprehensive overview of the effects of biotic stress factors, such as insect pests, bacterial, fungal, and viral pathogens, and nematodes, as well as abiotic stress factors, including extreme hot and cold temperature, drought, toxicity induced by heavy metal and salinity, on the antioxidant systems in cotton. We discuss the crucial antioxidants, such as glutathione, proline, and phenolics, and highlight major antioxidant enzymes, including ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR), and their roles in cotton's response to these stress factors. Furthermore, we explore the potential mechanisms and the crosstalk between different stress factors signaling pathways. We also examine the implications of stress-induced changes in antioxidant levels and enzyme activities for cotton productivity and breeding strategies. Additionally, we shed light on the unanswered questions, research gaps, and future perspectives in this field, paving the way for further investigations to enhance our understanding of cotton's antioxidant defenses and develop novel strategies for improving cotton stress tolerance and yield stability.

Endophytes in Agriculture: Potential to Improve Yields and Tolerances of Agricultural Crops

Endophytic fungi and bacteria live asymptomatically within plant tissues. In recent decades, research on endophytes has revealed that their significant role in promoting plants as endophytes has been shown to enhance nutrient uptake, stress tolerance, and disease resistance in the host plants, resulting in improved crop yields. Evidence shows that endophytes can provide improved tolerances to salinity, moisture, and drought conditions, highlighting the capacity to farm them in marginal land with the use of endophyte-based strategies. Furthermore, endophytes offer a sustainable alternative to traditional agricultural practices, reducing the need for synthetic fertilizers and pesticides, and in turn reducing the risks associated with chemical treatments. In this review, we summarise the current knowledge on endophytes in agriculture, highlighting their potential as a sustainable solution for improving crop productivity and general plant health. This review outlines key nutrient, environmental, and biotic stressors, providing examples of endophytes mitigating the effects of stress. We also discuss the challenges associated with the use of endophytes in agriculture and the need for further research to fully realise their potential.

Spatiotemporal variation of irrigation water requirements for grain crops under climate change in Northwest China

Clarifying the spatiotemporal variation of crop irrigation water requirement (IWR) under the background of climate change is an essential basis for water resource management, determining the irrigation quota and adjusting the planting structure. Using 61 years of climate data from 205 stations in Northwest China, this study investigated the spatiotemporal variations of climatic factors and IWR during the growth period of five main grain crops (spring wheat, winter wheat, spring maize, summer maize, and rice) and explored the dominant climatic driving factors of IWR variation. Results showed that (1) the IWR of grain crops showed distinct differences. Rice was the highest water consumption crop (mean of 753.78 mm), and summer maize was the lowest (mean of 452.90 mm). (2) The variation trends and average values of IWR of different grain crops have spatial heterogeneity across Northwest China. For most crops, high values and increasing trends of IWR were mainly located in eastern Xinjiang, western Gansu, and western Inner Mongolia. (3) T_max (maximum temperature), T_min (minimum temperature), and P_eff (effective precipitation) showed an increasing trend during the growth period of each grain crop, while U₁₀ (wind speed at 10 m height), SD (solar radiation), and RH (relative humidity) presented decreasing trends. (4) SD, T_max, and U₁₀ promoted the increase of grain crops' IWR, while P_eff and RH inhibited it. The impacts of climatic factors on the grain crop IWR differed among different regions. P_eff was the most influential factor to the IWR of all grain crops in most areas. Therefore, under the premise of a significant increase in T and uncertain precipitation mode in the future, it is urgent to take effective water-saving measures according to the irrigation needs of the region. To cope with the adverse impact of climate change on the sustainable development of agriculture in the northwest dry area, to ensure regional and national food security.

Silencing of GhORP_A02 enhances drought tolerance in Gossypium hirsutum

BACKGROUND

ORP (Oxysterol-binding protein-related proteins) genes play a role in lipid metabolism, vesicular transferring and signaling, and non-vesicular sterol transport. However, no systematic identification and analysis of ORP genes have been reported in cotton.

RESULT

In this study, we identified 14, 14, 7, and 7 ORP genes in G. hirsutum, G. barbadense, G. arboreum, and G. raimondii, respectively. Phylogenetic analysis showed that all ORP genes could be classified into four groups. Gene structure and conserved motif analysis suggest that the function of this gene family was conserved. The Ka/Ks analysis showed that this gene family was exposed to purifying selection during evolution. Transcriptome data showed that four ORP genes, especially GhORP_A02, were induced by abiotic stress treatment. The cis-acting elements in the ORP promoters were responsive to phytohormones and various abiotic stresses. The silenced plants of GhORP_A02 were more sensitive to drought stress when compared to control.

CONCLUSION

The major finding of this study shed light on the potential role of ORP genes in abiotic stress and provided a fundamental resource for further analysis in cotton.

Total and Mitochondrial Transcriptomic and Proteomic Insights into Regulation of Bioenergetic Processes for Shoot Fast-Growth Initiation in Moso Bamboo

As a fast-growing, woody grass plant, Moso bamboo (Phyllostachys edulis) can supply edible shoots, building materials, fibrous raw material, raw materials for crafts and furniture and so on within a relatively short time. Rapid growth of Moso bamboo occurs after the young bamboo shoots are covered with a shell and emerge from the ground. However, the molecular reactions of bioenergetic processes essential for fast growth remain undefined. Herein, total and mitochondrial transcriptomes and proteomes were compared between spring and winter shoots. Numerous key genes and proteins responsible for energy metabolism were significantly upregulated in spring shoots, including those involved in starch and sucrose catabolism, glycolysis, the pentose phosphate pathway, the tricarboxylic acid cycle and oxidative phosphorylation. Accordingly, significant decreases in starch and soluble sugar, higher ATP content and higher rates of respiration and glycolysis were identified in spring shoots. Further, the upregulated genes and proteins related to mitochondrial fission significantly increased the number of mitochondria, indirectly promoting intracellular energy metabolism. Moreover, enhanced alternate-oxidase and uncoupled-protein pathways in winter shoots showed that an efficient energy-dissipating system was important for winter shoots to adapt to the low-temperature environment. Heterologous expression of PeAOX1b in Arabidopsis significantly affected seedling growth and enhanced cold-stress tolerance. Overall, this study highlights the power of comparing total and mitochondrial omics and integrating physiochemical data to understand how bamboo initiates fast growth through modulating bioenergetic processes.

Ectopic Expression of the Allium cepa 1-SST Gene in Cotton Improves Drought Tolerance and Yield Under Drought Stress in the Field

In some plants, sucrose: sucrose 1-fructosyltransferase (1-SST) is the first irreversible key enzyme in fructan biosynthesis. Studies have shown that fructan accumulation enhances abiotic stress tolerance of plants. To investigate the role of 1-SST in drought stress responses, a total of 37 cotton plants expressing a 1-SST gene from Allium cepa were developed by Agrobacterium-mediated transformation. Under drought stress in the field, compared with wild-type, ectopic expression of Ac1-SST in cotton resulted in significantly higher soluble sugars (especially 1-kestose), proline and relative water contents, as well as decreased malondialdehyde content, which contributed to maintaining intracellular osmoregulation and reducing membrane damage. In addition, ectopic expression of Ac1-SST in cotton significantly improved the photosynthesis rate, performance of PSII (including Pn, Fv/Fm, WUE, ΦPSII, and PI_total) and plant growth under drought stress. Furthermore, compared with the wild-type, under the droughted field, the yield loss per square meter of transgenic cotton was reduced by an average of 20.9% over two consecutive years. Our results indicate that the Ac1-SST gene can be used to improve drought tolerance and yield of cotton varieties, and might also be a promising drought-resistant gene for improving other crop varieties.

Identification and characterization of the AINV genes in five Gossypium species with potential functions of GhAINVs under abiotic stress

Acid invertase (AINV) is a kind of sucrose hydrolase with an important role in plants. Currently, the AINV genes have not been systematically studied in cotton. In this study, a total of 92 AINV genes were identified in five cotton species. The phylogenetic analysis revealed that the AINV proteins were divided into two subgroups in cotton: vacuolar invertase (VINV) and cell wall invertase (CWINV). The analysis of gene structures, conserved motifs, and three-dimensional protein structures suggested that GhAINVs were significantly conserved. The synteny analysis showed that whole-genome duplication was the main force promoting the expansion of the AINV gene family. The cis-element, transcriptome, and quantitative real time-polymerase chain reaction (qRT-PCR) showed that some GhAINVs were possibly associated with stress response. GhCWINV4, highly expressed in PEG treatment, was cloned, and subsequent virus-induced gene silencing assay confirmed that this gene was involved in the drought stress response. Overall, this study might be helpful for further analyzing the biological function of AINVs and provide clues for improving the resistance of cotton to stress.

Drought and crop yield

Episodes of water shortage occur in most agricultural regions of the world. Their durations and intensities increase, and their seasonal timing alters with changing climate. During the ontogenic cycle of crop plants, each development stage, such as seed germination, seedling establishment, vegetative root and shoot growth, flowering, pollination and seed and fruit development, is specifically sensitive to dehydration. Desiccation threatens yield and leads to specific patterns, depending on the type of crop plant and the harvested plant parts, e.g. leafy vegetables, tubers, tap roots or fruits. This review summarizes the effects of drought stress on crop plants and relates the dehydration-dependent yield penalty to the harvested organ and tissue. The control of shoot transpiration and the reorganization of root architecture are of core importance for maintaining proper plant water relationships. Upon dehydration, the provision and partitioning of assimilates and the uptake and distribution of nutrients define remaining growth activity. Domestication of crops by selection for high yield under high input has restricted the genetic repertoire for achieving drought stress tolerance. Introgression of suitable alleles from wild relatives into commercial cultivars might improve the ability to grow with less water. Future research activities should focus more on field studies in order to generate more realistic improvements to crops. Robotic field phenotyping should be integrated into genetic mapping for the identification of relevant traits.

Effect of 4-chloro-2-methylphenoxy acetic acid on tomato gene expression and rhizosphere bacterial communities under inoculation with phosphate-solubilizing bacteria

The herbicide 4-chloro-2-methylphenoxy acetic acid (MCPA) is widely used to control the spread of broad-leaved weeds in agricultural soils, though it remains unclear how tomato plants cope with the phytotoxic effects of MCPA at the molecular level. In this study, RNA-seq and Illumina MiSeq were used to sequence bacterial communities in tomato rhizosphere soils treated with MCPA and the phosphate-solubilizing bacterial strain N3. The results showed that MCPA induced abnormal growth of lateral roots in tomato seedlings and reduced uptake of the nutrients N, P, and K as well as the hormone (ABA and GA3) levels. Inoculation with strain N3 increased nutrient uptake by roots and increased levels of the hormones ABA, ZEA, and JA in tomato seedlings and also increased the abundance of the phyla Proteobacteria and Gemmatimonadetes in soil under MCPA treatment. GO functional groups in which differentially expressed genes (DEGs) are involved included DNA binding transcription factor activity, transcriptional regulator activity, enzyme inhibitor activity, and cell wall biogenesis. The highest numbers of DEGs are annotated to ribosome, photosynthesis, and carbon metabolism categories. Our findings provide valuable information for the application of strain N3, which is beneficial for reducing the toxic effect of MCPA on vegetable plants.

Ovary Signals for Pollen Tube Guidance in Chalazogamous Mangifera indica L

Most flowering plants show porogamy in which the pollen tubes reach the egg apparatus through the micropyle. However, several species show chalazogamy, an unusual pollen tube growth, in which the pollen tubes reach the embryo sac through the chalaza. While ovary signals for pollen tube growth and guidance have been extensively studied in porogamous species, few studies have addressed the process in chalazogamous species such as mango (Mangifera indica L.), one of the five most important fruit crops worldwide in terms of production. In this study, we characterize pollen-pistil interaction in mango, paying special attention to three key players known to be involved in the directional pollen tube growth of porogamous species such as starch, arabinogalactan proteins (AGPs), and γ-aminobutyric acid (GABA). Starch grains were observed in the style and in the ponticulus at anthesis, but their number decreased 1 day after anthesis. AGPs, revealed by JIM8 and JIM13 antibodies, were homogenously observed in the style and ovary, but were more conspicuous in the nucellus around the egg apparatus. GABA, revealed by anti-GABA antibodies, was specifically observed in the transmitting tissue, including the ponticulus. Moreover, GABA was shown to stimulate in vitro mango pollen tube elongation. The results support the heterotrophic growth of mango pollen tubes in the style at the expense of starch, similarly to the observations in porogamous species. However, unlike porogamous species, the micropyle of mango does not show high levels of GABA and starch, although they were observed in the ponticulus and could play a role in supporting the unusual pollen tube growth in chalazogamous species.

Exogenous melatonin improves cotton (Gossypium hirsutum L.) pollen fertility under drought by regulating carbohydrate metabolism in male tissues

Although exogenous melatonin can enhance the drought tolerance of plants, reports on the role of melatonin in drought tolerance in male reproductive organs are limited. To explore this, a pot experiment was conducted with cotton cultivar Yuzaomian 9110 to study the effects of exogenous melatonin (100, 200, and 1000 μM) on male fertility and related carbohydrate metabolism in anther under drought. Results showed that drought inhibited the translocation of carbon assimilates to anthers, however, melatonin application (100 and 200 μM) significantly improved the translocation of carbon assimilates to drought-stressed anthers. Drought reduced the deposition of starch, the hydrolysis of sucrose into hexoses, the generation of adenosine triphosphate (ATP) in anthers, restricting pollen viability and germination. Nevertheless, the appropriate melatonin concentrations (100 and 200 μM) increased the starch accumulation by enhancing ADP-glucose pyrophosphorylase and soluble starch synthases activities and accelerated the hydrolysis of sucrose by increasing sucrose synthase, acid and alkaline invertases activities in drought-stressed anthers. Appropriate melatonin concentrations (100 and 200 μM) also could help to generate more ATP for reproductive activities of drought-stressed anthers, finally increasing the pollen viability and germination of drought-stressed plants. These findings suggest that drought inhibited male fertility of cotton, but a precise melatonin application could regulate the carbohydrate balance of drought-stressed anthers to improve male fertility. This is the first report demonstrating the important role of exogenous melatonin in improving male fertility under drought conditions by regulating the carbohydrate metabolism in the male part of cotton.

Acid invertase confers heat tolerance in rice plants by maintaining energy homoeostasis of spikelets

Heat stress impairs both pollen germination and pollen tube elongation, resulting in pollination failure caused by energy imbalance. Invertase plays a critical role in the maintenance of energy homoeostasis; however, few studies investigated this during heat stress. Two rice cultivars with different heat tolerance, namely, TLY83 (heat tolerant) and LLY722 (heat susceptible), were subjected to heat stress. At anthesis, heat stress significantly decreased spikelet fertility, accompanied by notable reductions in pollen germination on stigma and pollen tube elongation in ovule, especially in LLY722. Acid invertase (INV), rather than sucrose synthase, contributed to sucrose metabolism, which explains the different tolerances of both cultivars. Under heat stress, larger enhancements in NAD(H), ATP, and antioxidant capacity were found in TLY83 compared with LLY722, whereas a sharp reduction in poly(ADP-ribose) polymerase (PARP) activity was found in the former compared with the latter. Importantly, exogenous INV, 3-aminobenzamide (a PARP inhibitor), sucrose, glucose, and fructose significantly increased spikelet fertility under heat stress, where INV activity was enhanced and PARP activity was inhibited. Therefore, INV can balance the energy production and consumption to provide sufficient energy for pollen germination and pollen tube growth under heat stress.

Fertilization in flowering plants: an odyssey of sperm cell delivery

In light of the available discoveries in the field, this review manuscript discusses on plant reproduction mechanism and molecular players involved in the process. Sperm cells in angiosperms are immotile and are physically distant to the female gametophytes (FG). To secure the production of the next generation, plants have devised a clever approach by which the two sperm cells in each pollen are safely delivered to the female gametophyte where two fertilization events occur (by each sperm cell fertilizing an egg cell and central cell) to give rise to embryo and endosperm. Each of the successfully fertilized ovules later develops into a seed. Sets of macromolecules play roles in pollen tube (PT) guidance, from the stigma, through the transmitting tract and funiculus to the micropylar end of the ovule. Other sets of genetic players are involved in PT reception and in its rupture after it enters the ovule, and yet other sets of genes function in gametic fusion. Angiosperms have come long way from primitive reproductive structure development to today's sophisticated, diverse, and in most cases flamboyant organ. In this review, we will be discussing on the intricate yet complex molecular mechanism of double fertilization and how it might have been shaped by the evolutionary forces focusing particularly on the model plant Arabidopsis.

Influence of drought stress on pistil physiology and reproductive success of two Gossypium hirsutum cultivars differing in drought tolerance

The causes of reproductive failure under drought stress (DS) are poorly understood. We hypothesized that reproductive failure was related to drought-induced changes in pistil biochemistry. To address this hypothesis, a water deficit-induced experiment was conducted with two cotton cultivars (Dexiamian 1, drought tolerant; Yuzaomian 9110, drought sensitive). Results showed that DS decreased the photosynthesis of subtending leaf and downregulated sucrose transporter gene (GhSUT-1) expression in pistil for both cultivars, resulting in lower pistil carbon accumulation which was reflected in the decreased starch accumulation. Lower starch, as potential energy, and adenosine triphosphate (ATP), as direct energy, in droughted pistils suggested less energy for pollen tube entrance into ovules, reducing the fertilized ovule number and fertilization efficiency. Further, although pistil peroxidase activity increased under DS, a higher hydrogen peroxide (H₂ O₂ ) level still was measured in droughted pistils than well-watered pistils, damaging reproductive activities. Moreover, larger decreases in photosynthesis, pistil GhSUT-1 expression, carbon accumulation, starch and ATP contents caused by DS for Yuzaomian 9110 than Dexiamian 1, and different responses of superoxide dismutase and catalase activities, and ascorbic acid and H₂ O₂ contents to DS between the two cultivars might be the reasons causing a greater decrease in fertilization efficiency for Yuzaomian 9110 than Dexiamian 1 under DS. Thus, we suggest that decreased ovule fertilization under DS was related to the disorganized carbohydrate metabolism and inefficient antioxidant defense in droughted pistils, and the effects of DS on pistil carbohydrate metabolism and antioxidant defense were more significant for drought-sensitive cultivars than drought-tolerant cultivars.

Drought-induced disturbance of carbohydrate metabolism in anthers and male abortion of two Gossypium hirsutum cultivars differing in drought tolerance

Cotton pollen abortion, under drought stress, was closely associated with changes in anther carbohydrate metabolism, and pollen abortion rate due to drought was higher in drought-sensitive cultivars than drought-tolerant cultivars. Cotton reproductive failure under drought stress is intrinsically connected with altered male fertility, however, studies investigating the effect of drought stress on cotton male fertility are nonexistent. Thus, a drought stress experiment was conducted with two cotton cultivars, differing in drought tolerance, to study pollen fertility and anthers' physiology. Results indicated that drought stress reduced pollen fertility of both cultivars due to decreases in anther starch and adenosine triphosphate (ATP) synthesis. Lower assimilate supply capacity in conjunction with impaired activities of ADP-glucose pyrophosphorylase and soluble starch synthase were the main reasons for the decreased starch levels in drought-stressed anthers. The decreased activities of sucrose synthetase and acid invertase were responsible for the higher sucrose level in drought-stressed anthers than well-watered anthers and the changing trend of sucrose was intensified by the decreased expressions of sucrose synthase genes (GhSusA, GhSusB, GhSusD) and acid invertase genes (GhINV1, GhINV2). However, despite sucrose degradation being limited in drought-stressed anthers, glucose level was higher in droughted anthers than well-watered ones, and that might be attributed to the down-regulated respiration since decreased anther ATP levels were detected in drought-stressed plants. Furthermore, compared to the drought-tolerant cultivar, pollen fertility was more suppressed by drought stress for the drought-sensitive cultivar, and that was attributed to the larger decrease in starch and ATP contents.