Defensive Role of Plant Hormones in Advancing Abiotic Stress-Resistant Rice Plants

Consistent climatic perturbations have increased global environmental concerns, especially the impacts of abiotic stresses on crop productivity. Rice is a staple food crop for the majority of the world’s population. Abiotic stresses, including salt, drought, heat, cold and heavy metals, are potential inhibitors of rice growth and yield. Abiotic stresses elicit various acclimation responses that facilitate in stress mitigation. Plant hormones play an important role in mediating the growth and development of rice plants under optimal and stressful environments by activating a multitude of signalling cascades to elicit the rice plant’s adaptive responses. The current review describes the role of plant hormone-mediated abiotic stress tolerance in rice, potential crosstalk between plant hormones involved in rice abiotic stress tolerance and significant advancements in biotechnological initiatives including genetic engineering approach to provide a step forward in making rice resistance to abiotic stress.

Plant Hormone Resistance and Agronomic Characteristics of the MT10 Mutant in Rice

The MT10 mutant plants had resistances to auxin.Under light and dark culture,the roots of MT10 seedlings had shown less lateral roots and short lateral roots.In soil,MT10 seedlings had shown not only no changed agronomic characteristics but also no significant difference with WT.

Transcriptome analysis reveals effects of red and blue lightemitting diodes(LEDs)on the growth,chlorophyll fluorescence and endogenous plant hormones of potato(Solanum tuberosum L.)plantlets cultured in vitro

Red and blue light illumination has been reported to significantly affect plantlet growth.Potato is an important food and feed crop in the world and potato plantlet cultured in vitro plays an important role in potato production.However,few studies have documented the effects of red and blue light on the growth of potato plantlets revealed at the transcriptome level.The objective of this study was to determine the growth and physiological responses of potato plantlets cultured in vitro under monochromatic red(RR),monochromatic blue(BB)as well as combined red and blue(RB)LEDs using the RNA-Seq technique.In total,3150 and 814 differentially expressed genes(DEGs)were detected in potato plantlets under RR and BB,respectively,compared to RB(used as control).Compared to the control,the DEGs enriched in"photosynthesis"and"photosynthesis-antenna proteins"metabolic pathways were up-regulated and down-regulated by BB and RR,respectively,which might be responsible for the increases and decreases of maximum quantum yield(F_(v)/F_(m)),photochemical quantum yield(φ_(PSII)),photochemical quenching(q_(P))and electron transfer rate(ETR)in BB and RR,respectively.Potato plantlets exhibited dwarfed stems and extended leaves under BB,whereas elongated stems and small leaves were induced under RR.These dramatically altered plantlet phenotypes were associated with variable levels of endogenous plant hormones gibberellin(GAs),indoleacetic acid(IAA)and cytokinins(CKs),as assessed in stems and leaves of potato plantlets.In addition,monochromatic red and blue LEDs trigged the opposite expression profiles of DEGs identified in the"plant hormone signal transduction"metabolic pathway,which were closely related to the endogenous plant hormone levels in potato plantlets.Our results provide insights into the responses of potato plantlets cultured in vitro to red and blue LEDs at the transcriptomic level and may contribute to improvements in the micro-propagation of potato plantlets cultured in vitro from the light spectrum aspect.

Effects of Different Plant Hormones for Microbial Degradation of PASHs and Diesel under Aerobic Conditions

The effects of plant hormones for biodegradation of polycyclic aromatic sulfur heterocycles(PASHs)and diesel fuel were studied.Indole butyric acid(IBA)and gibberellin were found to promote biodegradation of DBT and diesel,respectively.Concentrations of plant hormones,pH,temperature,soil moisture and substrate concentrations were optimized in microbial metabolic processes.Two main factors including temperature and IBA concentration were determined by factor analysis in DBT biodegradation.And soil moisture and diesel concentration were important factors in diesel biodegradation.Binding sites between cell surface and DBT or diesel components were performed by molecular operating environment(MOE).This study suggested that plant hormones could be applied to effectively remove pollutants in environment.

Identification of the Regulator of G-Protein Signaling Protein Responsive to Plant Hormones and Abiotic Stresses in Brassica napus

Regulator of G protein signaling proteins （RGS） accelerate the rate of GTP hydrolysis by Gαproteins, thus acting as negative regulators of G-protein signaling. Studies on Arabidopsis and soybean have proven that RGS proteins are physiologically important in plants and contribute to the signaling pathways regulated by different stimuli. Brassica napus is an important agriculturally relevant plant, the wildly planted oilseed rape in the world, which possesses an identiifed Gα, Gβand Gγsubunits. In the present study, we identiifed and characterized a Brassica napus RGS gene, BnRGS1, which contained an open reading frame of 1 380 bp encoding a putative 52.6 kDa polypeptide of 459 amino acids, within seven putative transmembrane domains in the N-terminal and RGS box in the C-terminal. BnRGS1 is located on the membrane in onion epidermal cells and tobacco leaves, and interacts with BnGA1 in the mating-based split-ubiquitin system. The expression levels of BnRGS1 were quite different in different tissues and developmental stages, and induced by abscisic acid （ABA） and indole-3-acetic acid （IAA）. The effects of gibberellin （GA3） and brassinolide （BR） on the expression of BnRGS1 were irregular under the concentrations tested. Moreover, the transcript level of BnRGS1 was also induced by polyethylene glycol （PEG）, whereas remained little changed by 200 mmol L-1 NaCl. These results suggested that the BnRGS1 may be involved in B. napus response to plant hormone signaling and abiotic stresses.

Research and Applicationon Plant Hormone--Abscisic Acid, ABA

Abscisic Acid (ABA), along with ethylene, gibberellins, cytokinins and auxins, is regarded as five kinds of important plant hormone. ABA was first isolated from cotton bud by Addcott Ohhuma’s group in 1963. Until 1965, its plane structure was determined. It was formally named as Abscisic acid in "the International Conference of Plant Regulator" in 1967. Scientists all over the world have made a long-term unremitting effort

Epigenetic Modifications and Plant Hormone Action

The action of phytohormones in plants requires the spatiotemporal regulation of their accumulation and responses at various levels. Recent studies reveal an emerging relationship between the function of phytohormones and epigenetic modifications. In particular, evidence suggests that auxin biosynthesis, transport, and signal transduction is modulated by microRNAs and epigenetic factors such as histone modification, chromatin remodeling, and DNA methylation. Furthermore, some phytohormones have been shown to affect epigenetic modifications. These findings are shedding light on the mode of action of phytohormones and are opening up a new avenue of research on phytohormones as well as on the mech- anisms reaulatino eoioenetic modifications.

Structure and Activity of Strigolactones： New Plant Hormones with a Rich Future

Strigolactones （SLs） constitute a new class of plant hormones which are active as germination stimulants for seeds of parasitic weeds of Striga, Orobanche, and Pelipanchi spp, in hyphal branching of arbuscular mycorrhizal （AM） fungi and as inhibitors of shoot branching. In this review, the focus is on molecular features of these SLs. The occurrence of SLs in root exudates of host plants is described. The naming protocol for SL according to the International Union of Pure and Applied Chemistry （IUPAC） rules and the ＇at a glance＇ method is explained. The total synthesis of some natural SLs is described with details for all eight stereoisomers of strigol. The problems encountered with assign- ing the correct structure of natural SLs are analyzed for orobanchol, alectrol, and solanacol. The structure-activity relationship of SLs as germination stimulants leads to the identification of the bioactiphore of SLs. Together with a tentative mechanism for the mode of action, a model has been derived that can be used to design and prepare active SL analogs. This working model has been used for the preparation of a series of new SL analogs such as Nijmegen-1, and analogs derived from simple ketones, keto enols, and saccharine. The serendipitous finding of SL mimics which are derived from the D-ring in SLs （appropriately substituted butenolides） is reported. For SL mimics, a mode of action is proposed as well. Recent new results support this proposal. The stability of SLs and SL analogs towards hydrolysis is described and some details of the mechanism of hydrolysis are discussed as well. The attempted isolation of the protein receptor for germination and the current status concerning the biosynthesis of natural SLs are briefly discussed. Some non-SLs as germinating agents are mentioned. The structure-activity relationship for SLs in hyphal branching of AM fungi and in repression of shoot branching is also analyzed. For each of the principle functions, a working model for the design of new active SL analogs is described and its applicability and implications are discussed. It is shown that the three principal functions use a distinct perception system. The importance of stereochemistry for bioactivity has been described for the various functions.

Shaping Small Bioactive Molecules to Untangle Their Biological Function： A Focus on Fluorescent Plant Hormones

Modern biology overlaps with chemistry in explaining the structure and function of all cellular processes at the molecular level. Plant hormone research is perfectly located at the interface between these two disciplines, taking advantage of synthetic and computational chemistry as a tool to decipher the complex biological mechanisms regulating the action of plant hormones. These small signaling molecules regulate a wide range of developmental processes, adapting plant growth to ever changing environmental conditions. The synthesis of small bioactive molecules mimicking the activity of endogenous hormones allows us to unveil many molec- ular features of their functioning, giving rise to a new field, plant chemical biology. In this framework, fluores- cence labeling of plant hormones is emerging as a successful strategy to track the fate of these challenging molecules inside living organisms. Thanks to the increasing availability of new fluorescent probes as well as advanced and innovative imaging technologies, we are now in a position to investigate many of the dynamic mechanisms through which plant hormones exert their action. Such a deep and detailed comprehension is mandatory for the development of new green technologies for practical applications. In this review, we sum- marize the results obtained so far concerning the fluorescent labeling of plant hormones, highlighting the basic steps leading to the design and synthesis of these compelling molecular tools and their applications.

A comparative genomic analysis of plant hormone related genes in different species

Plant hormones are small molecules that play important roles throughout the life span of a plant, known as auxin, gibberellin, cyto- kinin, abscisic acid, ethylene, jasmonic acid, salicylic acid, and brassinosteroid. Genetic and molecular studies in the model organism Arabidopsis thaliana have revealed the individual pathways of various plant hormone responses. In this study, we selected 479 genes that were convincingly associated with various hormone actions based on genetic evidence. By using these 479 genes as queries, a genome-wide search for their orthologues in several species （microorganisms, plants and animals） was performed. Meanwhile, a com- parative analysis was conducted to evaluate their evolutionary relationship. Our analysis revealed that the metabolisms and functions of plant hormones are generally more sophisticated and diversified in higher plant species. In particular, we found that several phytohor- mone receptors and key signaling components were not present in lower plants or animals. Meanwhile, as the genome complexity in- creases, the orthologue genes tend to have more copies and probably gain more diverse functions. Our study attempts to introduce the classification and phylogenic analysis of phytohormone related genes, from metabolism enzymes to receptors and signaling components, in different species.

Synergistic effects of plant hormones on spontaneous late-ripening mutant of'Jinghong'peach detected by transcriptome analysis

Objectives:Peach(Prunus persica L.)is an ancient fruit tree that originated from China.It is the climacteric fruit belonging to genus Prunus in family Rosaceae.Ethylene,which is produced during ripening,accelerates fruit softening,and therefore peaches cannot be stored for a long time.Materials and Methods:To study the mechanism of fruit late ripening,transcriptome analysis of the fruit of a late-ripening mutant of'Jinghong'peach was performed to identify genes and pathways involved in fruit late ripening.Results:A total of 1805,1511,and 2309 genes were found to be differentially expressed in W2_vs_M1,W3_vs_M2,and W3_vs_M3,respectively.Functional enrichment analysis of the differentially expressed genes showed they were related to carotenoid biosynthesis,starch and sucrose metabolism plant hormone signal transduction,flavonoid biosynthesis,and photosynthesis.The expression trends of ripening-related genes that encode transcription factors and plant hormone signal transduction-related genes that encode enzymes were similar.Conclusions:It will help to elucidate the transcriptional regulatory network of fruit development in the spontaneous late-ripening mutant of‘Jinghong’peach and provide a theoretical basis for understanding the molecular regulatory mechanism of fruit ripening.

Broad Hormonal Responses Induced by Aluminum in Roots of Dwarf Transgenics of Solanum lycopersicum L. cv “Micro-Tom”

The spatial pattern distribution of plant hormones in response to aluminum (Al) toxicity in roots remains to be shown. This study was performed to assess the root hormonal accumulation and gene expression in response to Al toxicity in five transgenic miniature dwarf tomatoes cv. Micro-Tom (MT). MT and MT transgenics to acid indole acetic, cytokinin, gibberellin, abscisic acid and ethylene were cultivated in nutrient solutions containing different Al concentrations. Root growth elongation was measured and cellular damage was visualized by staining Evans’s blue. The GUS reporter gene staining technique was used to visualize hormonal changes in MT apex root tissues. Data indicated that the MT is sensitive to Al that induced significant growth inhibition and cellular damage. Al concentration of 27 μM was significantly toxic, inducing root apex darkening and inhibition of root development. The qualitative evaluation of GUS reporter gene expression showed intense crosstalk among all hormones studied, underscoring the complexity of signaling induced by Al in apex roots. Results point out to a major understanding of the hormonal signaling in response to Al toxicity, which may induce a change of root growth and architecture with growth inhibition and cell constraints modulated by all different hormones evaluated.

Origin, evolution, and molecular function of DELLA proteins in plants

Gibberellic acid(GA), a ubiquitous phytohormone, has various effects on regulators of plant growth and development. GAs promote growth by overcoming growth restraint mediated by DELLA proteins(DELLAs). DELLAs, in the GRAS family of plant-specific nuclear proteins, are nuclear transcriptional regulators harboring a unique N-terminal GA perception region for binding the GA receptor GIBBERELLIN INSENSITIVE DWARF1(GID1) and a C-terminal GRAS domain necessary for GA repression activity via interaction with multiple regulatory proteins. The N-terminal conserved region of DELLAs evolved to form a mode of GID1/DELLA-mediated GA signaling originating in bryophytes and ferns. Binding of GA to GID1 increases the affinity between DELLAs and a SCF E3 ubiquitin–ligase complex, thus promoting the eventual destruction of DELLAs by the 26 S proteasome. DELLAs negatively regulate GA response by releasing transcription factors to directly activate downstream genes and indirectly regulate GA biosynthesis genes increasing GA responsiveness and feedback control by promoting GID1 transcription. GA communicates extensively with other plant hormones and uses crosstalk to regulate plant growth and development. In this review, we summarize current understanding of evolutionary DELLA-mediated gibberellin signaling and functional diversification of DELLA, focusing primarily on interactions of DELLAs with diverse phytohormones.

Functions of Plant Growth Substances in the Growth of Dendrobium officinale Kimura et Migo

[Objectives] To study the effects of plant growth substance on the growth and development of Dendrobium officinale Kimura et Migo. [Methods] Comparative methods were applied to study the effects of plant growth substance on the growth and development of D. officinale Kimura et Migo. [Results] Plant growth regulators play an important role in the process of tissue culture rapid propagation of D. officinale Kimura et Migo,and the main regulatory pathways are as follows.( i) Plant growth regulators promote the growth and development of D. officinale Kimura et Migo through regulating the changes of its endogenous hormones.( ii) Plant growth regulators affect the accumulation of polysaccharide content in D. officinale Kimura et Migo through regulating the changes in chlorophyll content and enzymes involved in sucrose metabolism.( iii) Plant growth regulators can increase the activity of antioxidant enzymes of D. officinale Kimura et Migo,to increase its stress resistance. [Conclusions]Using molecular biology techniques,combined with the changes of plant hormones in D. officinale Kimura et Migo,and analysis on key enzyme in the synthesis of plant hormones and gene expression,it is feasible to study the rules o changes in the content of active content of D. officinale Kimura et Migo.

Effects of Phytohormones on Accumulation of ^(88)Sr in Sunflower(Helianthus annuus L.)

With Sunflower （ Helianthus annuus L.） as an experimental material, phytohormones were externally applied, so as to screen phytohormones capable of alleviating environmental stress. Three kinds of phytohormones （auxin IAA, gibberellin GA and salicylic acid SA） were added through pot culture. The results showed that the three phytohormones all improved the accumulation of ^88 Sr in sunflower plant, and increased the translocation and bioaccumulation factors of ^88 Sr; and under the 100 mg/LSA treatment, the adsorption capacity, TF and BCF of ^88 Sr in sunflower plant reached the highest values.

The Effect of Plastic-Covered Ridge and Furrow Planting on the Grain Filling and Hormonal Changes of Winter Wheat

Although plastic-covered ridge and furrow planting（RF） has been reported to produce substantial increases in the grain weight of winter wheat,the underlying mechanism is not yet understood.The present study used two cultivars,Xinong 538 and Zhoumai 18,and RF and traditional flatten planting（TF,control） with the objective of investigating the effect of RF on wheat grain filling and the possible relationship of hormonal changes in the wheat grains under RF to grain filling.The results indicated that RF significantly increased the grain weight,although the effects on grain filling were different： RF significantly increased the grain-filling rate and grain weight of inferior grains,whereas RF had no significant effect on grainfilling rate and grain weight of superior grains.The final grain weight of inferior grains under RF was 39.1 and 50.7 mg for Xinong 538 and Zhoumai 18,respectively,3.6 and 3.4 mg higher than the values under TF.However,the final grain weight of superior grains under RF was only 0.6 and 0.8 mg higher than under TF for Xinong 538 and Zhoumai 18,respectively.RF significantly decreased the ethylene and gibberellic acid content in the inferior grains and increased the indole-3-acetic acid,abscisic acid and zeatin ＋ zeatin riboside content in the inferior grains;however,no significant difference between RF and TF was observed for the hormonal content in the superior grains.Based on these results,we concluded that RF significantly modulated hormonal changes in the inferior grains and,thus,affected the grain filling and grain weight of the inferior grains;in contrast,RF had no significant effect on grain filling,grain weight and hormonal changes in the superior wheat grains.

Exogenous SA or 6-BA maintains photosynthetic activity in maize leaves under high temperature stress

With global warming, high-temperature(HT) stress has become a major abiotic stress for crops, in particular summer maize in China. Photosynthesis is sensitive to HT. Salicylic acid(SA) and 6-benzyladenine(6-BA) can improve the adaptation of plants to various biotic and abiotic stresses. However, their contribution to maintaining photosynthetic activity and alleviating photoinhibition in maize leaves under HT stress is still unclear. The effects of exogenous SA or 6-BA on growth, photosynthesis capacity, photosystem Ⅱ(PSII) activity, subcellular ultrastructure, antioxidant system, and plant hormones in maize leaves under HT stress were investigated. Under HT conditions, application of SA or 6-BA up-regulated gibberellin and zeatin content in leaves, increasing leaf area index(LAI). It also expanded the stomata by reducing abscisic acid and jasmonic acid content in leaves, cooling them and increasing CO2supply to photosynthesis. A higher net photosynthetic rate, combined with increased activity of the antioxidant system, alleviated oxidative stress in maize plants sprayed with SA or 6-BA, allowing them to maintain their chloroplast ultrastructure and PSII activity, in particular electron transfer from QAto QB. The increased LAI and net photosynthetic rate per unit leaf area also resulted in the accumulation of more biomass.

Integrative analysis of the transcriptome and metabolome reveals the response mechanism to tomato spotted wilt virus

Tomato spotted wilt virus(TSWV)is an important virus that has rapidly spread throughout the world.TSWV seriously hinders the production of tomato(Solanum lycopersicum)and other plants.In order to discover more new genes and metabolites related to TSWV resistance in tomato plants,the genes and metabolites related to the resistance of tomato plants inoculated with TSWV were identified and studied herein.The tomato TSWV-resistance line YNAU335(335)and TSWV-susceptible lines NO5 and 96172I(961)were used as the transcriptome and metabolome research materials.Transcriptomic and metabolomic techniques were used to analyze the gene and metabolite response mechanisms to TSWV inoculation.A total of 3566,2951,and 2674 differentially expressed genes(DEGs)were identified in lines 335,NO5,and961,respectively.Meanwhile,208,228,and 273 differentially accumulated metabolites(DAMs)were identified in lines 335,NO5,and 961,respectively.In line 335,the number of DEGs was the highest,but the number of DAMs was lowest.Furthermore,903 DEGs and 94 DAMs were common to the response to TSWV in the three inbred lines.The 903 DEGs and 94 DAMs were mainly enriched in the plant hormone signal transduction and flavonoid synthesis pathways.In addition,many nucleotide-binding site-leucine-rich repeat genes and transcription factors were found that might be involved in the TSWV response.These results provide new insights into TSWV resistance mechanisms.

Priming for Saline-Alkaline Tolerance in Rice:Current Knowledge and Future Challenges

Soil salinization and/or alkalization is a major constraint to crop production worldwide.Approximately 60% of the cultivated land is affected by salt,over half of which is alkalized.Alkaline soils are characterized by high alkalinity and typically high salinity,which creates a complex saline-alkaline(SA) stress that affects plant growth.Rice cultivation has been accepted as an important strategy for effective utilization of SA land if water is available for irrigation.Nevertheless,as a salt-sensitive plant,rice plants suffer severe SA-induced damage,which results in poor plant growth and grain yield.Various approaches have been employed to improve rice productivity in SA land.Among them,the priming technique has emerged as a powerful method for enhancing SA tolerance in rice plants.In this review,we summarized how SA stress damages rice plants,and then presented how priming treatment can mitigate such damage.

An in Vitro Approach to Investigate the Role of Abscisic Acid in Alleviating the Negative Effects of Chilling Stress on Banana Shoots

Banana is a tropical crop cultivated in warm places.Chilling stress in Egypt is making banana crops less productive.Abscisic acid(ABA),a key plant hormone,regulates metabolic and physiological processes and protects plants from a variety of stresses.In vitro growing banana shoots were pre-treated with ABA at four concentrations(0,25,50,and 100 mM)and chilled at 5℃for 24 h,followed by a six-day recovery period at 25℃.By comparing ABA treatments to both positive and negative controls,physiological and biochemical changes were investigated.Chilling stress(5℃)caused a considerable increase in lipid peroxidation and ion leakage and reduced photosynthetic pigments in cold-treated plantlets.Increasing the concentration of ABA to 100μM enhanced the response to chilling stress.ABA had a major effect on mitigating chilling injury in banana shoots by keeping cell membranes stable and lowering the amount of ion leakage and lipid peroxidation.Also,ABA significantly maintained the photosynthetic pigment concentration of banana shoots;accumulated higher amounts of total soluble carbohydrates and proline;and increased DPPH radical scavenging activity.Furthermore,ABA treatment enhanced cold tolerance in chilling-stressed banana shoots through the regulation of antioxidant enzyme activity.Overall,the results show that ABA is a good choice for protecting banana shoots from the damage caused by chilling stress.