Gibberellins and auxin regulate soybean hypocotyl elongation under low light and high-temperature interaction

Effect of seed priming with auxin on ROS detoxification and carbohydrate metabolism and their relationship with germination and early seedling establishment in salt stressed maize

As crucial stages in the plant ontogeny, germination and seedling establishment under adverse conditions greatly determine staple crop growth and productivity. In the context of green technologies aiming to improve crop yield, seed priming is emerging as an effective approach to enhance seed vigor and germination performance under salt stress. In this study, we assess the efficiency of seed priming with indole-3-acetic acid (IAA) in mitigating the adverse effects of salt stress on maize (Zea mays L.) seedlings during germination and early seedling stages. In unprimed seeds, salt stress reduced germination indices, and seedling (both radicle and coleoptile) growth, together with decreased tissue hydration. However, seed priming using IAA significantly improved maize salt response, as reflected by the increased seed germination dynamics, early seedling establishment, and water status. Besides, seedlings from IAA-primed seeds showed a higher activity of α-amylase, resulting in increased sugar contents in roots and coleoptiles of salt-stressed plants. Further, IAA-seed priming stimulated the accumulation of endogenous IAA in salt-stressed seedlings, in concomitance with a significant effect on reactive oxygen species detoxification and lipid peroxidation prevention. Indeed, our data revealed increased antioxidant enzyme activities, differentially regulated in roots and coleoptiles, leading to increased activities of the antioxidant enzymes (SOD, CAT and GPX). In summary, data gained from this study further highlight the potential of IAA in modulating early interactions between multiple signaling pathways in the seed, endowing maize seedlings with enhanced potential and sustained tolerance to subsequent salt stress.

Functions of Phytochrome Interacting Factors (PIFs) in Adapting Plants to Biotic and Abiotic Stresses

Plants possess the remarkable ability to sense detrimental environmental stimuli and launch sophisticated signal cascades that culminate in tailored responses to facilitate their survival, and transcription factors (TFs) are closely involved in these processes. Phytochrome interacting factors (PIFs) are among these TFs and belong to the basic helix-loop-helix family. PIFs are initially identified and have now been well established as core regulators of phytochrome-associated pathways in response to the light signal in plants. However, a growing body of evidence has unraveled that PIFs also play a crucial role in adapting plants to various biological and environmental pressures. In this review, we summarize and highlight that PIFs function as a signal hub that integrates multiple environmental cues, including abiotic (i.e., drought, temperature, and salinity) and biotic stresses to optimize plant growth and development. PIFs not only function as transcription factors to reprogram the expression of related genes, but also interact with various factors to adapt plants to harsh environments. This review will contribute to understanding the multifaceted functions of PIFs in response to different stress conditions, which will shed light on efforts to further dissect the novel functions of PIFs, especially in adaption to detrimental environments for a better survival of plants.

Integrated analysis of transcriptomic and proteomic data reveals novel regulators of soybean (Glycine max) hypocotyl development

Hypocotyl elongation directly affects the seedling establishment and soil-breaking after germination. In soybean (Glycine max ), the molecular mechanisms regulating hypocotyl development remain largely elusive. To decipher the regulatory landscape, we conducted proteome and transcriptome analysis of soybean hypocotyl samples at different development stages. Our results showed that during hypocotyl development, many proteins were with extreme high translation efficiency (TE) and may act as regulators. These potential regulators include multiple peroxidases and cell wall reorganisation related enzymes. Peroxidases may produce ROS including H2 O2 . Interestingly, exogenous H2 O2 application promoted hypocotyl elongation, supporting peroxidases as regulators of hypocotyl development. However, a vast variety of proteins were shown to be with dramatically changed TE during hypocotyl development, including multiple phytochromes, plasma membrane intrinsic proteins (PIPs) and aspartic proteases. Their potential roles in hypocotyl development were confirmed by that ectopic expression of GmPHYA1 and GmPIP1-6 in Arabidopsis thaliana affected hypocotyl elongation. In addition, the promoters of these potential regulatory genes contain multiple light/gibberellin/auxin responsive elements, while the expression of some members in hypocotyls was significantly regulated by light and exogenous auxin/gibberellin. Overall, our results revealed multiple novel regulatory factors of soybean hypocotyl elongation. Further research on these regulators may lead to new approvals to improve soybean hypocotyl traits.

Enhancement of osmotic stress tolerance in soybean seed germination by bacterial bioactive extracts

Soybean (Glycine max (L.) Merr.) is important to the global food industry; however, its productivity is affected by abiotic stresses such as osmosis, flooding, heat, and cold. Here, we evaluated the bioactive extracts of two biostimulant bacterial strains, Bacillus butanolivorans KJ40 and B. siamensis H30-3, for their ability to convey tolerance to osmotic stress in soybean seeds during germination. Soybean seeds were dip-treated in extracts of KJ40 (KJ40E) or H30-3 (H30-3E) and incubated with either 0% or 20% polyethylene glycol 6000 (PEG), simulating drought-induced osmotic stress. We measured malondialdehyde content as a marker for lipid peroxidation, as well as the activity of antioxidant enzymes, including catalase, glutathione peroxidase, and glutathione reductase, together with changes in sugars content. We also monitored the expression of genes involved in the gibberellic acid (GA)-biosynthesis pathway, and abscisic acid (ABA) signaling. Following osmotic stress in the extract-treated seeds, malondialdehyde content decreased, while antioxidant enzyme activity increased. Similarly, the expression of GA-synthesis genes, including GmGA2ox1 and GmGA3 were upregulated in KJ40E-dipped seeds at 12 or 6 h after treatment, respectively. The ABA signaling genes GmABI4 and GmDREB1 were upregulated in H30-3E- and KJ40E-treated seeds at 0 and 12 h after treatment under osmotic stress; however, GmABI5, GmABI4, and GmDREB1 levels were also elevated in the dip-treated seeds in baseline conditions. The GA/ABA ratio increased only in KJ40E-treated seeds undergoing osmotic stress, while glucose content significantly decreased in H30-3E-treated seeds at 24 h after treatment. Collectively, our findings indicated that dip-treatment of soybean seeds in KJ40E and H30-3E can enhance the seeds' resistance to osmotic stress during germination, and ameliorate cellular damage caused by secondary oxidative stress. This seed treatment can be used agriculturally to promote germination under drought stress and lead to increase crop yield and quality.

High-temperature stress in crops: male sterility, yield loss and potential remedy approaches

Global food security is one of the utmost essential challenges in the 21st century in providing enough food for the growing population while coping with the already stressed environment. High temperature (HT) is one of the main factors affecting plant growth, development and reproduction and causes male sterility in plants. In male reproductive tissues, metabolic changes induced by HT involve carbohydrates, lipids, hormones, epigenetics and reactive oxygen species, leading to male sterility and ultimately reducing yield. Understanding the mechanism and genes involved in these pathways during the HT stress response will provide a new path to improve crops by using molecular breeding and biotechnological approaches. Moreover, this review provides insight into male sterility and integrates this with suggested strategies to enhance crop tolerance under HT stress conditions at the reproductive stage.

Shade avoidance syndrome in soybean and ideotype toward shade tolerance

The shade avoidance syndrome (SAS) in soybean can have destructive effects on yield, as essential carbon resources reserved for yield are diverted to the petiole and stem for exaggerated elongation, resulting in lodging and susceptibility to disease. Despite numerous attempts to reduce the unfavorable impacts of SAS for the development of cultivars suitable for high-density planting or intercropping, the genetic bases and fundamental mechanisms of SAS remain largely unclear. The extensive research conducted in the model plant Arabidopsis provides a framework for understanding the SAS in soybean. Nevertheless, recent investigations suggest that the knowledge obtained from model Arabidopsis may not be applicable to all processes in soybean. Consequently, further efforts are required to identify the genetic regulators of SAS in soybean for molecular breeding of high-yield cultivars suitable for density farming. In this review, we present an overview of the recent developments in SAS studies in soybean and suggest an ideal planting architecture for shade-tolerant soybean intended for high-yield breeding.

Nitric oxide acts downstream of reactive oxygen species in phytomelatonin receptor 1 (PMTR1)-mediated stomatal closure in Arabidopsis

Reactive oxygen species (ROS) and nitric oxide (NO) are important signaling molecules regulating stomatal movements in plants. Melatonin (N-acetyl-5-methoxytryptamine) was found to induce stomatal closure via phytomelatonin receptor 1 (PMTR1)-mediated activation of ROS production. Here, we evaluated the interaction between ROS and NO in the melatonin-induced stomatal closure in Arabidopsis. The results showed that the exogenous melatonin-induced stomatal closure and NO production were abolished by carboxy-PTIO (cPTIO, a NO scavenger). Additionally, the mutant lines nitrate reductase 1 and 2 (nia1nia2) and NO-associated 1 (noa1) did not show melatonin-induced stomatal closure, indicating that the melatonin-mediated stomatal closure is dependent on NO. The application of H₂O₂ induced the NO production and stomatal closure in the presence or absence of melatonin. However, the melatonin-induced NO production was impaired in the rhohC and rbohD/F (NADPH oxidase respiratory burst oxidase homologs) mutant plants. Furthermore, the ROS levels in nia1nia2 and noa1 did not differ significantly from the wild type plants, indicating that NO is a downstream component in the melatonin-induced ROS production. Exogenous melatonin did not induce NO and ROS production in the guard cells of pmtr1 mutant lines, suggesting NO occurs downstream of ROS in the PMTR1-mediated stomatal closure in Arabidopsis. Taken together, the results presented here suggest that melatonin-induced stomatal closure via PMTR1-mediated signaling in the regulation of ROS and NO production in Arabidopsis.

Identification of potential light deficiency response regulators in endangered species Magnolia sinostellata

Magnolia sinostellata is one of the endangered species in China and largely suffers light deficiency stress in the understory of forest. However, the weak light response molecular mechanism remains unclear. More importantly, hub genes in the molecular network have not been pinpointed. To explore potential regulators in the mechanism, weighted gene co-expression network analysis (WGCNA) was performed to analysis the trancriptome data of M. sinostellata leaves subjected to weak light with different time points. Gene co-expression analysis illustrated that module 1, 2 and 3 were closely associated with light deficiency treatment, which. Gene ontology and KEGG analyses showed that genes in module 1 mainly participated in amino and nucleotide metabolism, module 2 mostly involved in carbon fixation and module 3 mostly regulated photosynthesis related pathways, among which 6, 7 and 8 hub genes were identified, respectively. Hub genes isoform_107196 in module 1 and isoform_55976 in module 2 were unique to M. sinostellata. This study found that light deficiency inhibited photosynthesis and stress tolerance, while improved carbon metabolism and flowering related pathways in M. sinostellata, which can impact its accumulation reserves of growth and reproduction in the next season. In addition, key shade response regulators identified in this study have laid a firm foundation for further investigation of shade response molecular mechanism and protection of other shade sensitive plants.

Wandering between hot and cold: temperature dose-dependent responses

Plants in most natural habitats are exposed to a continuously changing environment, including fluctuating temperatures. Temperature variations can trigger acclimation or tolerance responses, depending on the severity of the signal. To guarantee food security under a changing climate, we need to fully understand how temperature response and tolerance are triggered and regulated. Here, we put forward the concept that responsiveness to temperature should be viewed in the context of dose-dependency. We discuss physiological, developmental, and molecular examples, predominantly from the model plant Arabidopsis thaliana, illustrating monophasic signaling responses across the physiological temperature gradient.

Joint metabolome and transcriptome analysis of the effects of exogenous GA3 on endogenous hormones in sweet cherry and mining of potential regulatory genes

Gibberellin (GA) is an important phytohormone that can participate in various developmental processes of plants. The study found that application of GA₃ can induce parthenocarpy fruit and improve fruit set. However, the use of GA₃ affects endogenous hormones in fruits, thereby affecting fruit quality. This study mainly investigates the effect of exogenous GA₃ on endogenous hormones in sweet cherries. The anabolic pathways of each hormone were analyzed by metabolome and transcriptome to identify key metabolites and genes that affect endogenous hormones in response to exogenous GA₃ application. Results showed that exogenous GA₃ led to a significant increase in the content of abscisic acid (ABA) and GA and affected jasmonic acid (JA) and auxin (IAA). At the same time, the key structural genes affecting the synthesis of various hormones were preliminarily determined. Combined with transcription factor family analysis, WRKY genes were found to be more sensitive to the use of exogenous GA₃, especially the genes belonging to Group III (PaWRKY16, PaWRKY21, PaWRKY38, PaWRKY52, and PaWRKY53). These transcription factors can combine with the promoters of NCED, YUCCA, and other genes to regulate the content of endogenous hormones. These findings lay the foundation for the preliminary determination of the mechanism of GA₃'s effect on endogenous hormones in sweet cherry and the biological function of WRKY transcription factors.

Integrated genetic mapping and transcriptome analysis reveal the BnaA03.IAA7 protein regulates plant architecture and gibberellin signaling in Brassica napus L

A novel mutation in the BnaA03.IAA7 protein reduces plant height and enhances gibberellin signaling in Brassica napus L. Rapeseed (Brassica napus) is an excellent and important source for vegetable oil production, but its production is severely affected by lodging. Lodging hinders mechanization and decreases yield, and an ideal solution is semidwarf breeding. Limited by germplasm resources, semidwarf breeding developed slowly in rapeseed. In the current study, a mutant called sdA03 was isolated from EMS-mutagenized lines of Zhongshuang 11 (ZS11). The inheritance analysis showed that phenotypes of sdA03 were controlled by a single semidominant gene. Genetic mapping, RNA-seq and candidate gene analysis identified BnaA03.IAA7 as a candidate gene, and a function test confirmed that the mutated BnaA03.iaa7 regulates plant architecture in a dose-dependent manner. Yeast two-hybrid and transient expression experiments illustrated the P87L substitution in the GWPPV/I degron motif of BnaA03.iaa7 impaired the interaction between BnaA03.IAA7 and TIR1 proteins, and BnaA03.iaa7 prevented ARF from activating the auxin signaling pathway.The gibberellin (GA) content was higher in sdA03 hypocotyls than in those of ZS11. Further expression analysis showed more active gibberellin signaling in hypocotyl and richer expression of GA synthetic genes in root and cotyledon of sdA03 seedlings. Finally, a marker was developed based on the SNP found in BnaA03.iaa7 and used in molecular breeding. The study enriched our understanding of the architectural regulation of rapeseed and provided germplasm resources for breeding.

Dark secrets of phytomelatonin

Phytomelatonin is a newly identified plant hormone, and its primary functions in plant growth and development remain relatively poorly appraised. Phytomelatonin is a master regulator of reactive oxygen species (ROS) signaling and acts as a darkness signal in circadian stomatal closure. Plants exhibit at least three interrelated patterns of interaction between phytomelatonin and ROS production. Exogenous melatonin can induce flavonoid biosynthesis, which might be required for maintenance of antioxidant capacity under stress, after harvest, and in leaf senescence conditions. However, several genetic studies have provided direct evidence that phytomelatonin plays a negative role in the biosynthesis of flavonoids under non-stress conditions. Phytomelatonin delays flowering time in both dicot and monocot plants, probably via its receptor PMTR1 and interactions with the gibberellin, strigolactone, and ROS signaling pathways. Furthermore, phytomelatonin signaling also functions in hypocotyl and shoot growth in skotomorphogenesis and ultraviolet B (UV-B) exposure; the G protein α-subunit (Arabidopsis GPA1 and rice RGA1) and constitutive photomorphogenic1 (COP1) are important signal components during this process. Taken together, these findings indicate that phytomelatonin acts as a darkness signal with important regulatory roles in circadian stomatal closure, flavonoid biosynthesis, flowering, and hypocotyl and shoot growth.

Melatonin enhanced low-temperature combined with low-light tolerance of pepper (Capsicum annuum L.) seedlings by regulating root growth, antioxidant defense system, and osmotic adjustment

Melatonin (MT) is an important biologically active hormone that plays a vital role in plant growth and development. In particular, it has been investigated for its roles in abiotic stress management. In this study, pepper seedlings were subjected to low-temperature combined with low-light stress (LL) (15/5°C, 100 μmol m^-2s^-1) prior to a foliar spray of 200mM MT for 168h to investigate the protective role of MT in pepper seedlings. Our results demonstrated that LL stress negatively affected root growth, and accelerated the accumulation of reactive oxygen species (ROS), including H₂O₂ and O 2 - , changed the osmolytes contents, and antioxidative system. However, these were reversed by exogenous MT application. MT effectively promoted the root growth as indicated by significant increase in root length, surface area, root volume, tips, forks, and crossings. In addition, MT reduced the burst of ROS and MDA contents induced by LL, enhanced the activities of SOD, CAT, POD, APX, DHAR, and MDHAR resulted by upregulated expressions of CaSOD, CaPOD, CaCAT, CaAPX, CaDHAR, and CaMDHAR, and elevated the contents of AsA and GSH, declined DHA and GSSH contents, which prevented membrane lipid peroxidation and protected plants from oxidative damages under LL stress. Furthermore, seedlings treated with MT released high contents of soluble sugar and soluble protein in leave, which might enhance LL tolerance by maintaining substance biosynthesis and maintaining cellular homeostasis resulted by high levels of osmolytes and carbohydrate in the cytosol. Our current findings confirmed the mitigating potential of MT application for LL stress by promoting pepper root growth, improving antioxidative defense system, ascorbate-glutathione cycle, and osmotic adjustment.

Roles of Auxin in the Growth, Development, and Stress Tolerance of Horticultural Plants

Auxin, a plant hormone, regulates virtually every aspect of plant growth and development. Many current studies on auxin focus on the model plant Arabidopsis thaliana, or on field crops, such as rice and wheat. There are relatively few studies on what role auxin plays in various physiological processes of a range of horticultural plants. In this paper, recent studies on the role of auxin in horticultural plant growth, development, and stress response are reviewed to provide novel insights for horticultural researchers and cultivators to improve the quality and application of horticultural crops.

Foliar Application of NH4 +/NO3 - Ratios Enhance the Lodging Resistance of Soybean Stem by Regulating the Physiological and Biochemical Mechanisms Under Shade Conditions

Shading is one of the most chronic restrains which can lead to the lodging of intercropped plants. In order to increase the soybean stem lodging resistance, a 2-year field trial was conducted to evaluate the impact of different ratios and concentrations of NH₄ ⁺/NO₃ ^- on the morpho-physiological and biochemical characteristics of soybean stem under shade conditions. The total 5 ratios of NH₄ ⁺/NO₃ ^- were applied as follows: T0 = 0/0 (control), T1 = 0/100 (higher ratio), T2 = 25/75 (optimum), T3 = 50/50 (optimum), and T4 = 75/25 (higher ratio) as a nitrogen source. Our findings displayed that the T2 (25/75) and T3 (50/50) treatments alleviated the shading stress by improving the photosynthetic activity, biomass accumulation, carbohydrates contents, and lignin related enzymes (POD, CAD, and 4Cl) which led to improvement in stem lodging resistance. The correlation analysis (p ≤ 0.05, p ≤ 0.01) revealed the strong relationship between lodging resistance index and stem diameter, stem strength, lignin content, photosynthesis, and lignin related enzymes (POD, CAD, and 4CL) evidencing the strong contribution of lignin and its related enzymes in the improvement of lodging resistance of soybean stem under shade conditions. Collectively, we concluded that optimum NH₄ ⁺/NO₃ ^- ratios (T2 and T3) can boost up the lodging resistance of soybean stem under shade stress.

Plant Development of Early-Maturing Spring Wheat (Triticum aestivum L.) under Inoculation with Bacillus sp. V2026

The effect of a plant growth-promoting bacterium (PGPB) Bacillus sp. V2026, a producer of indolyl-3-acetic acid (IAA) and gibberellic acid (GA), on the ontogenesis and productivity of four genotypes of early-maturing spring wheat was studied under controlled conditions. The inoculation of wheat plants with Bacillus sp. V2026 increased the levels of endogenous IAA and GA in wheat of all genotypes and the level of trans-Zeatin in Sonora 64 and Leningradskaya rannyaya cvs but decreased it in AFI177 and AFI91 ultra-early lines. Interactions between the factors “genotype” and “inoculation” were significant for IAA, GA, and trans-Zeatin concentrations in wheat shoots and roots. The inoculation increased the levels of chlorophylls and carotenoids and reduced lipid peroxidation in leaves of all genotypes. The inoculation resulted in a significant increase in grain yield (by 33–62%), a reduction in the time for passing the stages of ontogenesis (by 2–3 days), and an increase in the content of macro- and microelements and protein in the grain. Early-maturing wheat genotypes showed a different response to inoculation with the bacterium Bacillus sp. V2026. Cv. Leningradskaya rannyaya was most responsive to inoculation with Bacillus sp. V2026.

CsRCI2D enhances high-temperature stress tolerance in Camelina sativa L. through endo-membrane trafficking from the plasma membrane

Rare Cold Inducible 2s (RCI2s) are hydrophobic proteins in cell membranes that participate in abiotic stress tolerance mechanisms. Additionally, they are used as traceable membrane trafficking markers in endocytosis studies. Plants regulate cell homeostasis through endocytosis by limiting the activity of plasma membrane transporter proteins to adapt to stressful conditions. In this study, we found high temperature (HT) stress-induced membrane trafficking of RCI2D in Camelina sativa L. The gene expression and protein synthesis were increased by HT stress at 37 °C. Moreover, rapid membrane trafficking of CsRCI2D was traced by multiple-phase membrane fractionation using sucrose density gradients and compared with CsRCI2E/F/G from the same protein family subgroup. The distribution of CsRCI2s was shown to be similar to that of the clathrin heavy chain, which is known as a major endocytosis protein. Subcellular localization of CsRCI2D was observed in the plasma membrane and endo-membranes and overlapped with membrane lipids. CsRCI2D co-localized with lipids, and its overexpression increased the intracellular lipid content compared to that of wild-type camelina. Moreover, transgenic camelina lines showed enhanced HT stress tolerance during germination and hypocotyl elongation when compared to the wild type. These results suggest that HT-induced CsRCI2D membrane trafficking enhances HT stress tolerance in camelina.

Effect of Light Intensity on Morphology, Photosynthesis and Carbon Metabolism of Alfalfa (Medicago sativa) Seedlings

To understand how light intensity influences plant morphology and photosynthesis in the forage crop alfalfa (Medicago sativa L. cv. Zhongmu 1), we investigated changes in leaf angle orientation, chlorophyll fluorescence, parameters of photosynthesis and expression of genes related to enzymes involved in photosynthesis, the Calvin cycle and carbon metabolism in alfalfa seedlings exposed to five light intensities (100, 200, 300, 400 and 500 μmol m⁻² s⁻¹) under hydroponic conditions. Seedlings grown under low light intensities had significantly increased plant height, leaf hyponasty, specific leaf area, photosynthetic pigments, leaf nitrogen content and maximal PSII quantum yield, but the increased light-capturing capacity generated a carbon resource cost (e.g., decreased carbohydrates and biomass accumulation). Increased light intensity significantly improved leaf orientation toward the sun and upregulated the genes for Calvin cycle enzymes, thereby increasing photosynthetic capacity. Furthermore, high light (400 and 500 μmol m⁻² s⁻¹) significantly enhanced carbohydrate accumulation, accompanied by gene upregulation and increased activity of sucrose and starch-synthesis-related enzymes and those involved in carbon metabolism. Together, these results advance our understanding of morphological and physiological regulation in shade avoidance in alfalfa, which would guide the identification of suitable spatial planting patterns in the agricultural system.

Deciphering Novel Transcriptional Regulators of Soybean Hypocotyl Elongation Based on Gene Co-expression Network Analysis

Hypocotyl elongation is the key step of soybean seed germination, as well an important symbol of seedling vitality, but the regulatory mechanisms remain largely elusive. To address the problem, bioinformatics approaches along with the weighted gene co-expression network analysis (WGCNA) were carried out to elucidate the regulatory networks and identify key regulators underlying soybean hypocotyl elongation at transcriptional level. Combining results from WGCNA, yeast one hybridization, and phenotypic analysis of transgenic plants, a cyan module significantly associated with hypocotyl elongation was discerned, from which two novel regulatory submodules were identified as key candidates underpinning soybean hypocotyl elongation by modulating auxin and light responsive signaling pathways. Taken together, our results constructed the regulatory network and identified novel transcriptional regulators of soybean hypocotyl elongation based on WGCNA, which provide new insights into the global regulatory basis of soybean hypocotyl elongation and offer potential targets for soybean improvement to acquire cultivars with well-tuned hypocotyl elongation and seed germination vigor.

Adaptation Strategies to Improve the Resistance of Oilseed Crops to Heat Stress Under a Changing Climate: An Overview

Temperature is one of the decisive environmental factors that is projected to increase by 1. 5°C over the next two decades due to climate change that may affect various agronomic characteristics, such as biomass production, phenology and physiology, and yield-contributing traits in oilseed crops. Oilseed crops such as soybean, sunflower, canola, peanut, cottonseed, coconut, palm oil, sesame, safflower, olive etc., are widely grown. Specific importance is the vulnerability of oil synthesis in these crops against the rise in climatic temperature, threatening the stability of yield and quality. The natural defense system in these crops cannot withstand the harmful impacts of heat stress, thus causing a considerable loss in seed and oil yield. Therefore, a proper understanding of underlying mechanisms of genotype-environment interactions that could affect oil synthesis pathways is a prime requirement in developing stable cultivars. Heat stress tolerance is a complex quantitative trait controlled by many genes and is challenging to study and characterize. However, heat tolerance studies to date have pointed to several sophisticated mechanisms to deal with the stress of high temperatures, including hormonal signaling pathways for sensing heat stimuli and acquiring tolerance to heat stress, maintaining membrane integrity, production of heat shock proteins (HSPs), removal of reactive oxygen species (ROS), assembly of antioxidants, accumulation of compatible solutes, modified gene expression to enable changes, intelligent agricultural technologies, and several other agronomic techniques for thriving and surviving. Manipulation of multiple genes responsible for thermo-tolerance and exploring their high expressions greatly impacts their potential application using CRISPR/Cas genome editing and OMICS technology. This review highlights the latest outcomes on the response and tolerance to heat stress at the cellular, organelle, and whole plant levels describing numerous approaches applied to enhance thermos-tolerance in oilseed crops. We are attempting to critically analyze the scattered existing approaches to temperature tolerance used in oilseeds as a whole, work toward extending studies into the field, and provide researchers and related parties with useful information to streamline their breeding programs so that they can seek new avenues and develop guidelines that will greatly enhance ongoing efforts to establish heat stress tolerance in oilseeds.

A high concentration of abscisic acid inhibits hypocotyl phototropism in Gossypium arboreum by reducing accumulation and asymmetric distribution of auxin

Hypocotyl phototropism is mediated by the phototropins and plays a critical role in seedling morphogenesis by optimizing growth orientation. However, the mechanisms by which phototropism influences morphogenesis require additional study, especially for polyploid crops such as cotton. Here, we found that hypocotyl phototropism was weaker in Gossypium arboreum than in G. raimondii (two diploid cotton species), and LC-MS analysis indicated that G. arboreum hypocotyls had a higher content of abscisic acid (ABA) and a lower content of indole-3-acetic acid (IAA) and bioactive gibberellins (GAs). Consistently, the expression of ABA2, AAO3, and GA2OX1 was higher in G. arboreum than in G. raimondii, and that of GA3OX was lower; these changes promoted ABA synthesis and the transformation of active GA to inactive GA. Higher concentrations of ABA inhibited the asymmetric distribution of IAA across the hypocotyl and blocked the phototropic curvature of G. raimondii. Application of IAA or GA3 to the shaded and illuminated sides of the hypocotyl enhanced and inhibited phototropic curvature, respectively, in G. arboreum. The application of IAA, but not GA, to one side of the hypocotyl caused hypocotyl curvature in the dark. These results indicate that the asymmetric distribution of IAA promotes phototropic growth, and the weakened phototropic curvature of G. arboreum may be attributed to its higher ABA concentrations that inhibit the action of auxin, which is regulated by GA signaling.

Study on the Regulatory Effects of GA3 on Soybean Internode Elongation

Excessive plant height is an important factor that can lead to lodging, which is closely related to soybean yield. Gibberellins are widely used as plant growth regulators in agricultural production. Gibberellic acid (GA₃), one of the most effective active gibberellins, has been used to regulate plant height and increase yields. The mechanism through which GA₃ regulates internode elongation has been extensively investigated. In 2019 and 2020, we applied GA₃ to the stems, leaves, and roots of two soybean cultivars, Heinong 48 (a high-stalk cultivar) and Henong 60 (a dwarf cultivar), and GA₃ was also applied to plants whose apical meristem was removed or to girded plants to compare the internode length and stem GA₃ content of soybean plants under different treatments. These results suggested that the application of GA₃ to the stems, leaves, and roots of soybean increased the internode length and GA₃ content in the stems. Application of GA₃ decreased the proportion of the pith in the soybean stems and primary xylem while increasing the proportion of secondary xylem. The apical meristem is an important site of GA₃ synthesis in soybean stems and is involved in the regulation of stem elongation. GA₃ was shown to be transported acropetally through the xylem and laterally between the xylem and phloem in soybean stems. We conclude that the GA₃ level in stems is an important factor affecting internode elongation.

McMYB4 improves temperature adaptation by regulating phenylpropanoid metabolism and hormone signaling in apple

Temperature changes affect apple development and production. Phenylpropanoid metabolism and hormone signaling play a crucial role in regulating apple growth and development in response to temperature changes. Here, we found that McMYB4 is induced by treatment at 28 °C and 18 °C, and McMYB4 overexpression results in flavonol and lignin accumulation in apple leaves. Yeast one-hybrid (Y1H) assays and electrophoretic mobility shift assays (EMSAs) further revealed that McMYB4 targets the promoters of the flavonol biosynthesis genes CHS and FLS and the lignin biosynthesis genes CAD and F5H. McMYB4 expression resulted in higher levels of flavonol and lignin biosynthesis in apple during growth at 28 °C and 18 °C than during growth at 23 °C. At 28 °C and 18 °C, McMYB4 also binds to the AUX/ARF and BRI/BIN promoters to activate gene expression, resulting in acceleration of the auxin and brassinolide signaling pathways. Taken together, our results demonstrate that McMYB4 promotes flavonol biosynthesis and brassinolide signaling, which decreases ROS contents to improve plant resistance and promotes lignin biosynthesis and auxin signaling to regulate plant growth. This study suggests that McMYB4 participates in the abiotic resistance and growth of apple in response to temperature changes by regulating phenylpropanoid metabolism and hormone signaling.

A mutation in CsHY2 encoding a phytochromobilin (PΦB) synthase leads to an elongated hypocotyl 1(elh1) phenotype in cucumber (Cucumis sativus L.)

The elongated hypocotyl1 (elh1) mutant in cucumber is due to a mutation in CsHY2, which is a homolog of the Arabidopsis HY2 encoding the phytochromobilin (PΦB) synthase for phytochrome biosynthesis Hypocotyl length is a critical determinant in establishing high quality seedlings for successful cucumber production, but knowledge on the molecular regulation of hypocotyl growth in cucumber is very limited. Here, we reported identification and characterization of a cucumber elongated hypocotyl 1 (elh1) mutant. We found that the longer hypocotyl in elh1 was due to longitudinal growth of hypocotyl cells. With fine mapping, the elh1 locus was delimited to a 20.9-kb region containing three annotated genes; only one polymorphism was identified in this region between two parental lines, which was a non-synonymous SNP (G28153633A) in the third exon of CsHY2 (CsGy1G030000) that encodes a phytochromobilin (PΦB) synthase. Uniqueness of the mutant allele at CsHY2 was verified in natural cucumber populations. Ectopic expression of CsHY2 in Arabidopsis hy2-1 long-hypocotyl mutant led to reduced hypocotyl length. The PΦB protein was targeted to the chloroplast. The expression levels of CsHY2 and five phytochrome genes CsPHYA1, CsPHYA2, CsPHYB, CsPHYC and CsPHYE were all significantly down-regulated while several cell elongation related genes were up-regulated in elh1 mutant compared to wild-type cucumber, which are correlated with dynamic hypocotyl elongation in the mutant. RNA-seq analysis in the WT and mutant revealed differentially expressed genes involved in porphyrin and chlorophyll metabolisms, cell elongation and plant hormone signal transduction pathways. This is the first report to characterize and clone the CsHY2 gene in cucumber. This work reveals the important of CsHY2 in regulating hypocotyl length and extends our understanding of the roles of CsHY2 in cucumber.

The Heat is On: How Crop Growth, Development and Yield Respond to High Temperature

Plants are exposed to a wide range of temperatures during their life cycle and need to continuously adapt. These adaptations need to deal with temperature changes on a daily and seasonal level and with temperatures affected by climate change. Increasing global temperatures negatively impact crop performance, and several physiological, biochemical, morphological and developmental responses to increased temperature have been described that allow plants to mitigate this. In this review, we assess various growth, development, and yield-related responses of crops to extreme and moderate high temperature, focusing on knowledge gained from both monocot (e.g. wheat, barley, maize, rice) and dicot crops (e.g. soybean and tomato) and incorporating information from model plants (e.g. Arabidopsis and Brachypodium). This revealed common and different responses between dicot and monocot crops, and defined different temperature thresholds depending on the species, growth stage and organ.

Temperature regulation of plant hormone signaling during stress and development

Global climate change has broad-ranging impacts on the natural environment and human civilization. Increasing average temperatures along with more frequent heat waves collectively have negative effects on cultivated crops in agricultural sectors and wild species in natural ecosystems. These aberrantly hot temperatures, together with cold stress, represent major abiotic stresses to plants. Molecular and physiological responses to high and low temperatures are intricately linked to the regulation of important plant hormones. In this review, we shall highlight our current understanding of how changing temperatures regulate plant hormone pathways during immunity, stress responses and development. This article will present an overview of known temperature-sensitive or temperature-reinforced molecular hubs in hormone biosynthesis, homeostasis, signaling and downstream responses. These include recent advances on temperature regulation at the genomic, transcriptional, post-transcriptional and post-translational levels - directly linking some plant hormone pathways to known thermosensing mechanisms. Where applicable, diverse plant species and various temperature ranges will be presented, along with emerging principles and themes. It is anticipated that a grand unifying synthesis of current and future fundamental outlooks on how fluctuating temperatures regulate important plant hormone signaling pathways can be leveraged towards forward-thinking solutions to develop climate-smart crops amidst our dynamically changing world.

The impact of global dimming on crop yields is determined by the source-sink imbalance of carbon during grain filling

Global dimming reduces incident global radiation but increases the fraction of diffuse radiation, and thus affects crop yields; however, the underlying mechanisms of such an effect have not been revealed. We hypothesized that crop source-sink imbalance of either carbon (C) or nitrogen (N) during grain filling is a key factor underlying the effect of global dimming on yields. We presented a practical framework to assess both C and N source-sink relationships, using data of biomass and N accumulation from periodical sampling conducted in field experiments for wheat and rice from 2013 to 2016. We found a fertilization effect of the increased diffuse radiation fraction under global dimming, which alleviated the negative impact of decreased global radiation on source supply and sink growth, but the source supply and sink growth were still decreased by dimming, for both C and N. In wheat, the C source supply decreased more than the C sink demand, and as a result, crops remobilized more pre-heading C reserves, in response to dimming. However, these responses were converse in rice, which presumably stemmed from the more increment in radiation use efficiency and the more limited sink size in rice than wheat. The global dimming affected source supply and sink growth of C more significantly than that of N. Therefore, yields in both crops were dependent more on the source-sink imbalance of C than that of N during grain filling. Our revealed source-sink relationships, and their differences and similarities between wheat and rice, provide a basis for designing strategies to alleviate the impact of global dimming on crop productivity.

Gravity Reduced Nitrogen Uptake via the Regulation of Brace Unilateral Root Growth in Maize Intercropping

Water, nutrient, light, and interspecific facilitation regulation of soil physicochemical properties and root morphology modulate nitrogen (N) uptake in cereal and legume intercropping systems. However, maize root morphological plasticity and N uptake capability response to gravity in the intercropping system remains to be determined. In this study, maize was grown under 20 cm (I₂₀), 40 cm (I₄₀), and 60 cm (I₆₀) of narrow row spacing in an intercropping system (maize-soybean strip relay intercropping) and equal row spacing of monoculture (M) in a 2-year field experiment. As a supplementary for the field experiment, maize root barrier and plant inclination experiments were conducted. Plant inclination, brace root morphology, N uptake, indole-3-acetic acid (IAA) level, IAA synthesis genes, and grain yield were assessed. The result showed that the plant inclination increased with decreasing narrow row spacing in intercropping system. Also, the brace unilateral root growth ratio (BURR) increased with increasing plant inclination in intercropping treatments. The plant inclination experiment showed the BURR achieved 94% after inclination at 45°. BURR tended to be positively correlated (p = 0.00) with plant inclination. Thus, gravity (plant inclination) causes brace unilateral root growth. The IAA concentration of stem nodes in the wide row increased with increasing plant inclination, while the IAA accumulation decreased in the narrow row. The Zmvt2 and ZM2G141383 genes (associated with IAA biosynthesis) were highly expressed in a wide row. There was a strong correlation (p = 0.03) between the IAA concentration of wide row and the BURR. Therefore, gravity regulates the IAA level, which affects BURR. In addition, the brace root number, volume, and surface area were decreased when BURR was increased. Subsequently, the leaf N, cob N, and kernel N accumulation were reduced. These organs N and grain yield in I₆₀ were not significantly different as compared to the control treatment. The excessive brace unilateral root growth was not conducive to N uptake and increased yield. Our results suggest that gravity is essential in regulating root morphology plasticity by regulating IAA levels and decreasing N uptake capacity. Furthermore, these results indicate that plant inclination can regulate root phenotype and N uptake of maize and by adjusting the spacing of narrow maize row, we can improve the N uptake and yield of the maize-soybean strip relay-intercropping system.

Aux/IAA14 Regulates microRNA-Mediated Cold Stress Response in Arabidopsis Roots

The phytohormone auxin and microRNA-mediated regulation of gene expressions are key regulators of plant growth and development at both optimal and under low-temperature stress conditions. However, the mechanistic link between microRNA and auxin in regulating plant cold stress response remains elusive. To better understand the role of microRNA (miR) in the crosstalk between auxin and cold stress responses, we took advantage of the mutants of Arabidopsis thaliana with altered response to auxin transport and signal. Screening of the mutants for root growth recovery after cold stress at 4 °C revealed that the auxin signaling mutant, solitary root 1 (slr1; mutation in Aux/IAA14), shows a hypersensitive response to cold stress. Genome-wide expression analysis of miRs in the wild-type and slr1 mutant roots using next-generation sequencing revealed 180 known and 71 novel cold-responsive microRNAs. Cold stress also increased the abundance of 26-31 nt small RNA population in slr1 compared with wild type. Comparative analysis of microRNA expression shows significant differential expression of 13 known and 7 novel miRs in slr1 at 4 °C compared with wild type. Target gene expression analysis of the members from one potential candidate miR, miR169, revealed the possible involvement of miR169/NF-YA module in the Aux/IAA14-mediated cold stress response. Taken together, these results indicate that SLR/IAA14, a transcriptional repressor of auxin signaling, plays a crucial role in integrating miRs in auxin and cold responses.

Heterogeneous Light Conditions Reduce the Assimilate Translocation Towards Maize Ears

The border row crop in strip intercropped maize is often exposed to heterogeneous light conditions, resulting in increased photosynthesis and yield decreased. Previous studies have focused on photosynthetic productivity, whereas carbon allocation could also be one of the major causes of decreased yield. However, carbon distribution remains unclear in partially shaded conditions. In the present study, we applied heterogeneous light conditions (T), and one side of plants was shaded (T-30%), keeping the other side fully exposed to light (T-100%), as compared to control plants that were exposed entirely to full-light (CK). Dry weight, carbon assimilation, ¹³C abundance, and transport tissue structure were analyzed to clarify the carbon distribution in partial shading of plants. T caused a marked decline in dry weight and harvest index (HI), whereas dry weight in unshaded and shaded leaves did not differ. Net photosynthesis rate (Pn), the activity of sucrose phosphate synthase enzymes (SPS), and sucrose concentration increased in unshaded leaves. Appropriately, 5.7% of the ¹³C from unshaded leaves was transferred to shaded leaves. Furthermore, plasmodesma density in the unshaded (T-100%) and shaded (T-30%) leaves in T was not significantly different but was lower than that of CK. Similarly, the vascular bundle total area of T was decreased. ¹³C transfer from unshaded leaves to ear in T was decreased by 18.0% compared with that in CK. Moreover, ¹³C and sucrose concentration of stem in T were higher than those in CK. Our results suggested that, under heterogeneous light, shaded leaves as a sink imported the carbohydrates from the unshaded leaves. Ear and shaded leaf competed for carbohydrates, and were not conducive to tissue structure of sucrose transport, resulting in a decrease in the carbon proportion in the ear, harvest index, and ear weight.