Ethylene Receptor Research Articles

Soluble and membrane-bound protein carrier mediate direct copper transport to the ethylene receptor family

The plant hormone ethylene is a key regulator of plant growth, development and stress adaption. Ethylene perception and response are mediated by a family of integral membrane receptors (ETRs) localized at the ER-Golgi network. The biological function of these receptors relies on a protein-bound copper cofactor. Nonetheless, molecular processes and structures controlling assembly and integration of the metal into the functional plant hormone receptor are still unknown. Here, we have explored the molecular pathways of copper transfer from the plant cytosol to the ethylene receptor family by analyzing protein–protein interactions of receptors with soluble and membrane-bound plant copper carriers. Our results suggest that receptors primarily acquire their metal cofactor from copper transporter RESPONSIVE-TO-ANTAGONIST-1 (RAN1) which has been loaded with the transition metal beforehand by soluble copper carriers of the ATX1-family. In addition, we found evidence for a direct interaction of ETRs with soluble chaperones ANTIOXIDANT-1 (ATX1) and COPPER TRANSPORT PROTEIN (CCH) raising the possibility of a direct copper exchange between soluble chaperones and receptors.

Control of Organ Abscission and Other Cell Separation Processes by Evolutionary Conserved Peptide Signaling.

Plants both generate and shed organs throughout their lifetime. Cell separation is in function during opening of anthers to release pollen; floral organs are detached after pollination when they have served their purpose; unfertilized flowers are shed; fruits and seeds are abscised from the mother plant to secure the propagation of new generations. Organ abscission takes place in specialized abscission zone (AZ) cells where the middle lamella between adjacent cell files is broken down. The plant hormone ethylene has a well-documented promoting effect on abscission, but mutation in ethylene receptor genes in Arabidopsis thaliana only delays the abscission process. Microarray and RNA sequencing have identified a large number of genes differentially expressed in the AZs, especially genes encoding enzymes involved in cell wall remodelling and disassembly. Mutations in such genes rarely give a phenotype, most likely due to functional redundancy. In contrast, mutation in the INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) blocks floral organ abscission in Arabidopsis. IDA encodes a small peptide that signals through the leucine-rich repeat receptor-like kinases HAESA (HAE) and HAE-LIKE2 (HSL2) to control floral organ abscission and facilitate lateral root emergence. Untimely abscission is a severe problem in many crops, and in a more applied perspective, it is of interest to investigate whether IDA-HAE/HSL2 is involved in other cell separation processes and other species. Genes encoding IDA and HSL2 orthologues have been identified in all orders of flowering plants. Angiosperms have had enormous success, with species adapted to all kinds of environments, adaptations which include variation with respect to which organs they shed. Here we review, from an evolutionary perspective, the properties of the IDA-HAE/HSL2 signaling module and the evidence for its hypothesized involvement in various cell separation processes in angiosperms.

Transcriptomic analysis reveals key factors in fruit ripening and rubbery texture caused by 1-MCP in papaya

BackgroundEthylene promotes fruit ripening whereas 1-methylcyclopropene (1-MCP), a non-toxic antagonist of ethylene, delays fruit ripening via the inhibition of ethylene receptor. However, unsuitable 1-MCP treatment can cause fruit ripening disorders.ResultsIn this study, we show that short-term 1-MCP treatment (400 nL•L− 1, 2 h) significantly delays papaya fruit ripening with normal ripening characteristics. However, long-term 1-MCP treatment (400 nL•L− 1, 16 h) causes a “rubbery” texture of fruit. The comparative transcriptome analysis showed that a total of 5529 genes were differently expressed during fruit ripening compared to freshly harvested fruits. Comprehensive functional enrichment analysis showed that the metabolic pathways of carbon metabolism, plant hormone signal transduction, biosynthesis of amino acids, and starch and sucrose metabolism are involved in fruit ripening. 1-MCP treatment significantly affected fruit transcript levels. A total of 3595 and 5998 differently expressed genes (DEGs) were identified between short-term 1-MCP, long-term 1-MCP treatment and the control, respectively. DEGs are mostly enriched in the similar pathway involved in fruit ripening. A large number of DEGs were also identified between long-term and short-term 1-MCP treatment, with most of the DEGs being enriched in carbon metabolism, starch and sucrose metabolism, plant hormone signal transduction, and biosynthesis of amino acids. The 1-MCP treatments accelerated the lignin accumulation and delayed cellulose degradation during fruit ripening. Considering the rubbery phenotype, we inferred that the cell wall metabolism and hormone signal pathways are closely related to papaya fruit ripening disorder. The RNA-Seq output was confirmed using RT-qPCR by 28 selected genes that were involved in cell wall metabolism and hormone signal pathways.ConclusionsThese results showed that long-term 1-MCP treatment severely inhibited ethylene signaling and the cell wall metabolism pathways, which may result in the failure of cell wall degradation and fruit softening. Our results reveal multiple ripening-associated events during papaya fruit ripening and provide a foundation for understanding the molecular mechanisms underlying 1-MCP treatment on fruit ripening and the regulatory networks.

Different expression of ATP-dependent RNA helicases in artificially and naturally induced mango fruitlet abscission

Premature fruit drop is a severe production constraint for mango (Mangifera indica) and recent research demonstrates that various physiological parameters and genes are involved in the abscission process. In addition to hormone and carbohydrate responses in the fruitlet, it is evident that ethylene receptors are involved in abscission zone activation. The mango ethylene receptors MiERS1 and MiETR1 respond differently to abscission-inducing ethephon treatments and their expression pattern indicates plant organ specificity. The study regarding the position of those receptors in the mango genome revealed two putative ATP-dependent RNA helicases, which are located upstream of MiERS1. RNA helicases are important for RNA metabolism, post-transcriptional modulation and gene expression. The mango helicase ADRH 7-1 was downregulated in pedicels of fruitlets prone to natural abscission but upregulated in the pedicel abscission zone after ethephon treatment. In contrast, ADRH 7-2 was not responsive to treatments and its transcription level was not significantly changed in the abscission zone. When ethephon-induced fruitlet abscission is compared to naturally induced abscission there are certain differences in the helicase gene expression pattern, as well as in the ethylene receptor expression pattern, while other physiological responses are known to be similar. The presented expression pattern of the ATP-dependent RNA helicase ADRH 7-1 indicates that it might play a role in the transcriptional regulation of the pedicel abscission zone.

Simultaneous Inhibition of Ethylene Biosynthesis and Binding Using AVG and 1-MCP in Two Rose Cultivars with Different Sensitivities to Ethylene

The primary factors that determine the longevity of cut roses are variable and depend on a cultivar’s sensitivity to ethylene. The vase life of ethylene-sensitive cultivars (SENS) is shortened by ethylene synthesis, while for ethylene-insensitive cultivars (INSENS) it is strongly related to water stress. In this study, we determined the effect of ethylene binding on the change in ethylene sensitivity in two rose cultivars with different sensitivities to the hormone. In addition, we determined the effects of ethylene binding and synthesis inhibition on flower senescence and gene expression using 1-methylcyclopropene (1-MCP) and aminoethoxyvinylglycine (AVG). The relationship between the mRNA levels of ethylene biosynthesis, receptor, and signaling genes and the degree of ethylene sensitivity was determined during flower development and senescence. The results showed that simultaneous treatment with AVG and 1-MCP effectively improved water balance, maintained leaf chlorophyll fluorescence ratios, and consequently extended the vase life of cut flowers for both SENS and INSENS cultivars. The results also revealed that the expression of the ethylene biosynthesis (RhACS2 and RhACO1) genes in cut roses was effectively suppressed by simultaneous treatments with both AVG and 1-MCP. The ethylene-induced induction of RhETR1-5 transcript levels and the degradation of RhCTR1-2 were both repressed by AVG and 1-MCP treatments; consequently, RhEIN3s transcripts were greatly inhibited in both SENS and INSENS cultivars. The findings from the current study revealed that a simultaneous inhibition of ethylene binding and synthesis suppressed plant responses to ethylene and consequently extended the vase life for cut rose flowers in both ethylene-sensitive and ethylene-insensitive cultivars.

Structural Model of the ETR1 Ethylene Receptor Transmembrane Sensor Domain

The structure, mechanism of action and copper stoichiometry of the transmembrane sensor domain of the plant ethylene receptor ETR1 and homologs have remained elusive, hampering the understanding on how the perception of the plant hormone ethylene is transformed into a downstream signal. We generated the first structural model of the transmembrane sensor domain of ETR1 by integrating ab initio structure prediction and coevolutionary information. To refine and independently validate the model, we determined protein-related copper stoichiometries on purified receptor preparations and explored the helix arrangement by tryptophan scanning mutagenesis. All-atom molecular dynamics simulations of the dimeric model reveal how ethylene can bind proximal to the copper ions in the receptor, illustrating the initial stages of the ethylene perception process.

The molecular mechanism for the ethylene regulation of postharvest button mushrooms maturation and senescence

The button mushroom (Agaricus bisporus) produces ethylene and respiration climacteric bursts coupling with rapidly maturation and senescence during postharvest storage. However, the molecular mechanism for the ethylene regulation of button mushroom maturation and senescence is still unclear. In this study, postharvest button mushrooms were treated with ethephon and the plant ethylene receptor inhibitor 1-methylcyclopropene (1-MCP), and the results showed that ethylene accelerated postharvest mushroom maturation and senescence and upregulated maturation- and senescence-related genes, which was in contrast to the effect of 1-MCP. Plant ethylene response elements were predicted in the promoter regions of all 19 maturation- and senescence-related genes in the button mushroom, and the 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO) gene promoter region contained three ethylene response elements, which all expressed the GUS gene in transgenic onion epidermal cells by exogenous ethylene induction. The ACO gene was also highly expressed in postharvest mushrooms by ethylene induction. The results suggest that the ethylene response elements harbored in the promoter regions of the maturation- and senescence-related genes are probably responsible for the ethylene and respiration bursts as well as maturation and senescence of the postharvest button mushroom. The molecular mechanism for the ethylene regulation of postharvest button mushroom maturation and senescence may be similar to that of climacteric fruits.

Molecular Analysis of Protein-Protein Interactions in the Ethylene Pathway in the Different Ethylene Receptor Subfamilies.

Signal perception and transmission of the plant hormone ethylene are mediated by a family of receptor histidine kinases located at the Golgi-ER network. Similar to bacterial and other plant receptor kinases, these receptors work as dimers or higher molecular weight oligomers at the membrane. Sequence analysis and functional studies of different isoforms suggest that the ethylene receptor family is classified into two subfamilies. In Arabidopsis, the type-I subfamily has two members (ETR1 and ERS1) and the type-II subfamily has three members (ETR2, ERS2, and EIN4). Whereas subfamily-I of the Arabidopsis receptors and their interactions with downstream elements in the ethylene pathway has been extensively studied in the past; related information on subfamily-II is sparse. In order to dissect the role of type-II receptors in the ethylene pathway and to decode processes associated with this receptor subfamily on a quantitative molecular level, we have applied biochemical and spectroscopic studies on purified recombinant receptors and downstream elements of the ethylene pathway. To this end, we have expressed purified ETR2 as a prototype of the type-II subfamily, ETR1 for the type-I subfamily and downstream ethylene pathway proteins CTR1 and EIN2. Functional folding of the purified receptors was demonstrated by CD spectroscopy and autokinase assays. Quantitative analysis of protein-protein interactions (PPIs) by microscale thermophoresis (MST) revealed that ETR2 has similar affinities for CTR1 and EIN2 as previously reported for the subfamily-I prototype ETR1 suggesting similar roles in PPI-mediated signal transfer for both subfamilies. We also used in planta fluorescence studies on transiently expressed proteins in Nicotiana benthamiana leaf cells to analyze homo- and heteromer formation of receptors. These studies show that type-II receptors as well as the type-I receptors form homo- and heteromeric complexes at these conditions. Notably, type-II receptor homomers and type-II:type-I heteromers are more stable than type-I homomers as indicated by their lower dissociation constants obtained in microscale thermophoresis studies. The enhanced stability of type-II complexes emphasizes the important role of type-II receptors in the ethylene pathway.

Alteration of nutritional and antioxidant level of ethylene receptor tomato mutants, Sletr1-1 and Sletr1-2

New ethylene insensitive mutant alleles, Sletr1-1 and Sletr1-2 which have a mutation at the first and second transmembrane domain of ethylene receptor gene of SlETR1, have a potential characteristic in improving postharvest life of tomato fruits. This study elucidates the impact of Sletr1-1 and Sletr1-2 mutation in alternating nutritional and antioxidant levels of tomato fruits at three stages of fruit maturation. The result showed that Sletr1-1 and Sletr1-2 mutations significantly reduced water content, total soluble solid and total sugar content and increased the titratable acidity independently of the tomato maturation. Those mutations also reduced lycopene, β-carotene, flavonoid content dependently of the tomato maturation, but did not change the total polyphenols content and antioxidant activity independently of the tomato maturation. These results indicate that ethylene has an important role in the alteration of nutritional and antioxidant levels during fruit ripening and the inhibition of ethylene perception due to SlETR1 mutation negatively impacting nutritional and antioxidant levels.

Omics analysis of the ethylene signal transduction in tomato as a function of storage temperature

This study has focussed on the effect of low temperature storage on the postharvest ripening of green tomatoes; more specifically, on the ethylene signal transduction in relation to the ethylene biosynthesis pathway. To this end, the first elements of the ethylene signal transduction, ethylene receptors, CTR and EIN2 have been analysed in tomatoes stored at three different temperatures in terms of both their gene and protein expression levels. These results have been related to quality changes and enzymes and intermediates of the ethylene biosynthesis pathway to better understand the ethylene control of ripening under low temperatures. The first changes observed during low temperature storage took place at the ethylene biosynthesis level, which might enhance changes in the ethylene signal transduction. Although expression of most ethylene signalling genes decreased with chilling, none of the protein levels showed a significant decrease, pointing at a differential regulation at the gene and protein level.

The ethylene receptor regulates Typha angustifolia leaf aerenchyma morphogenesis and cell fate.

Ethylene receptor is crucial for PCD and aerenchyma formation in Typha angustifolia leaves. Not only does it receive and deliver the ethylene signal, but it probably can determine the cell fate during aerenchyma morphogenesis, which is due to the receptor expression quantity. Aquatic plant oxygen delivery relies on aerenchyma, which is formed by a programmed cell death (PCD) procedure. However, cells in the outer edge of the aerenchyma (palisade cells and septum cells) remain intact, and the mechanism is unclear. Here, we offer a hypothesis: cells that have a higher content of ethylene receptors do not undergo PCD. In this study, we investigated the leaf aerenchyma of the aquatic plant Typha angustifolia. Ethephon and pyrazinamide (PZA, an inhibitor of ACC oxidase) were used to confirm that ethylene is an essential hormone for PCD of leaf aerenchyma cells in T. angustifolia. That the ethylene receptor was an indispensable factor in this PCD was confirmed by 1-MCP (an inhibitor of the ethylene receptor) treatment. Although PCD can be avoided by blocking the ethylene receptor, excessive ethylene receptors also protect cells from PCD. TaETR1, TaETR2 and TaEIN4 in the T. angustifolia leaf were detected by immunofluorescence (IF) using polyclonal antibodies. The result showed that the content of ethylene receptors in PCD-unsusceptible cells was 4-14 times higher than that one in PCD-susceptible cells, suggesting that PCD-susceptible cells undergo the PCD programme, while PCD-unsusceptible cells do not due to the content difference in the ethylene receptor in different cells. A higher level of ethylene receptor content makes the cells insensitive to ethylene, thereby avoiding cell death and degradation.

Impacts of Sletr1-1 and Sletr1-2 mutations on the hybrid seed quality of tomatoes

Shelf life is an important breeding trait in tomato, especially for the tomato production in subtropical and tropical regions. Previously we have isolated and characterized ethylene receptor mutants, Sletr1-1 and Sletr1-2 from mutant population based on Micro-Tom cultivar. Sletr1-1 showed insensitivity to ethylene while Sletr1-2 showed reduced sensitivity to ethylene. We also have demonstrated that the traits are useful for extending fruit shelf life of the hybrid tomato cultivars. For commercializing the hybrid cultivars, the seed quality is another important trait. In this study, we evaluated the effects of the Sletr1-1 and Sletr1-2 mutations on the seed quality characteristics of F1 hybrid lines generated by crossing Sletr1-1 and Sletr1-2 with three commercial tomato cultivars, Intan, Mutiara and Ratna. Sletr1-1 mutation conferred insensitivity to ethylene in the F1 hybrid seedlings, resulting in negative effects including reduced germination rate, vigor index and emergence speed index. Interestingly Sletr1-2 mutation had almost no effect on the seed quality characteristics of the F1 hybrid lines, suggesting that Sletr1-2 was suitable for producing high quality of hybrid seeds.

Differential Expression of Ethylene Signaling and Biosynthesis Genes in Floral Organs Between Ethylene-Sensitive and -Insensitive Rose Cultivars

The plant hormone ethylene regulates diverse aspects of plant growth and development, including flower senescence and abscission. In cut roses, the impact of ethylene on flower senescence varies greatly depending on the ethylene sensitivity of the floral organs, which is determined by the variety of the rose. To understand the relationship between ethylene synthesis and sensitivity in floral organs, we examined tissue-specific differences in gene expression and regulation using two rose cultivars with differing ethylene sensitivity. We monitored the expression patterns of genes related to ethylene biosynthesis (RhACS1, RhACS2, RhACS3, RhACS4, and RhACO1), receptor (RhETR1, RhETR2, RhETR3, RhETR4, and RhETR5), and signaling (RhCTR1, RhCTR2, RhEIN3-1, RhEIN3-2, and RhEIN3-3) in various floral organs of ethylene-sensitive (SENS; ‘All For Love’) and -insensitive (INSENS; ‘Peach Valley’) rose cultivars. The expression of ethylene-related genes in all floral organs was generally higher in SENS than INSENS cultivars. The presence of exogenous ethylene accelerated the accumulation of RhACS1-4 and RhACO1 transcripts in SENS petals and leaves and in INSENS stamens and stigmas, leading to an increase in RhETR1-5 expression in the floral organs. Meanwhile, RhCTR1-2 expression decreased considerably, with a consequent increase in RhEIN3 transcripts in SENS petals and leaves and INSENS stamens and stigmas. The differential expression of ethylene- related genes in the same tissues indicates that the site of initiation of the ethylene-inducible responses varies among the varieties, and this is probably related to the ethylene sensitivity of the flowers.

ETR1/RDO3 Regulates Seed Dormancy by Relieving the Inhibitory Effect of the ERF12-TPL Complex on DELAY OF GERMINATION1 Expression.

The control of seed dormancy by ethylene has been well studied, but the underlying molecular mechanisms are not fully understood. Here, we report the characterization of the Arabidopsis (Arabidopsis thaliana) mutant reduced dormancy 3 (rdo3) and the cloning of the underlying gene. We demonstrate that rdo3 is a loss-of-function mutant of the ethylene receptor ETHYLENE RESPONSE1 (ETR1). ETR1 controls seed dormancy partially through the DELAY OF GERMINATION1 (DOG1) pathway. Molecular and genetic analyses demonstrated that ETHYLENE RESPONSE FACTOR12 (ERF12) is involved in the regulation of seed dormancy downstream of ETR1. ERF12 interacts with TOPLESS (TPL) and genetically requires TPL to function. ERF12 and TPL repress the expression of DOG1 by occupying its promoter. Thus, we identified the dormancy pathway ETR1-ERF12-TPL-DOG1 and provide mechanistic insights into the regulation of seed dormancy by linking the ethylene and DOG1 pathways.

Wide transcriptional investigation unravel novel insights of the on-tree maturation and postharvest ripening of \u2018Abate Fetel\u2019 pear fruit

To decipher the transcriptomic regulation of the on-tree fruit maturation in pear cv. ‘Abate Fetel’, a RNA-seq transcription analysis identified 8939 genes differentially expressed across four harvesting stages. These genes were grouped into 11 SOTA clusters based on their transcriptional pattern, of which three included genes upregulated while the other four were represented by downregulated genes. Fruit ripening was furthermore investigated after 1 month of postharvest cold storage. The most important variation in fruit firmness, production of ethylene and volatile organic compounds were observed after 5 days of shelf-life at room temperature following cold storage. The role of ethylene in controlling the ripening of ‘Abate Fetel’ pears was furthermore investigated through the application of 1-methylcyclopropene, which efficiently delayed the progression of ripening by reducing fruit softening and repressing both ethylene and volatile production. The physiological response of the interference at the ethylene receptor level was moreover unraveled investigating the expression pattern of 12 candidate genes, initially selected to validate the RNA-seq profile. This analysis confirmed the effective role of the ethylene competitor in downregulating the expression of cell wall (PG) and ethylene-related genes (ACS, ACO, ERS1, and ERS2), as well as inducing one element involved in the auxin signaling pathway (Aux/IAA), highlighting a possible cross-talk between these two hormones. The expression patterns of these six elements suggest their use as molecular toolkit to monitor at molecular level the progression of the fruit on-tree maturation and postharvest ripening.

Influence of the ethylene‐related signal‐inhibiting octapeptide NOP‐1 on postharvest ripening and quality of ‘Golden Delicious’ apples

Processes extending the shelf life of climacteric fruit play an important role in terms of a sustainable global food supply. In a previous study, a synthetic octapeptide (NOP-1) was shown to inhibit the interaction between ethylene receptor (ETR) and ethylene insensitive-2 (EIN2), and in consequence delay tomato ripening. We investigated for the first time the effect of NOP-1 on inhibiting the ripening of apples ('Golden Delicious') during postharvest. Using purified recombinant proteins from a bacterial expression system, we demonstrate here that EIN2 also interacts tightly (Kd = 136 ± 29 nmol L-1 ) with the corresponding apple ETR MdETR1. In line with previous binding studies on tomato ETRs, the ripening-delaying peptide NOP-1 clearly binds to the purified apple ETR. An NOP-1 solution (1000 µmol L-1 ) was applied with a brush or microdispenser and compared with apples treated with 1-methylcyclopropene (1-MCP) (SmartFresh™, Agrofresh) applied as gaseous treatment or untreated control fruits. NOP-1 inhibited colour development and chlorophyll degradation during shelf life. These effects were more pronounced with the brush application (surface film) than with microdroplets application (mimicking a sprayable formulation). NOP-1 did not alter ethylene release or respiration rate, whereas 1-MCP expectedly strongly suppressed both. There were no differences in quality parameters evaluated. Our study shows that NOP-1 binds to MdETR1 which results in delaying of ethylene-dependent ripening developments of skin colour and chlorophyll. Besides application methods, possible reasons for the weak effect of NOP-1 in comparison with previous tomato experiments could be different receptor affinity and penetration differences. © 2019 Society of Chemical Industry.

The NOP-1 peptide derived from the central regulator of ethylene signaling EIN2 delays floral senescence in cut flowers

The plant hormone ethylene was identified as important triggering factor and primary regulator of flower senescence in many species. Consequently, application of chemical inhibitors of ethylene biosynthesis and action is used to extend the longevity of ethylene-sensitive flowers. Here, we show that the peptide NOP-1, a biological derived from the nuclear localization signal of ethylene regulator EIN2 tightly binds to the ethylene receptor of carnation plants - a model to study flower senescence. When applied on cut flowers the peptide biological delays petal senescence similar to previously identified and currently used chemical inhibitors, but offers significant advances to these chemicals in biodegradability, sustainability and ecotoxicity. Our bioinformatic analysis of a wide range of ethylene receptors indicates complete sequence conservation of the anticipated NOP-1 binding site in flower species supporting a widespread use of the peptide on flowering ornamentals to delay senescence and decay in cut flowers. We anticipate our innovative approach to extend flower longevity by a new class of biomolecules such as peptides, peptide analogues and peptide mimetics will significantly advance our technological capability to delay flower senescence and expand vase-life of cut flowers in a sustainable and environmentally friendly manner.

12-Oxo-Phytodienoic Acid Acts as a Regulator of Maize Defense against Corn Leaf Aphid.

The corn leaf aphid (CLA; Rhopalosiphum maidis) is a phloem sap-sucking insect that attacks many cereal crops, including maize (Zea mays). We previously showed that the maize inbred line Mp708, which was developed by classical plant breeding, provides enhanced resistance to CLA. Here, using electrophysiological monitoring of aphid feeding behavior, we demonstrate that Mp708 provides phloem-mediated resistance to CLA. Furthermore, feeding by CLA on Mp708 plants enhanced callose deposition, a potential defense mechanism utilized by plants to limit aphid feeding and subsequent colonization. In maize, benzoxazinoids (BX) or BX-derived metabolites contribute to enhanced callose deposition by providing heightened resistance to CLA. However, BX and BX-derived metabolites were not significantly altered in CLA-infested Mp708 plants, indicating BX-independent defense against CLA. Evidence presented here suggests that the constitutively higher levels of 12-oxo-phytodienoic acid (OPDA) in Mp708 plants contributed to enhanced callose accumulation and heightened CLA resistance. OPDA enhanced the expression of ethylene biosynthesis and receptor genes, and the synergistic interactions of OPDA and CLA feeding significantly induced the expression of the transcripts encoding Maize insect resistance1-Cysteine Protease, a key defensive protein against insect pests, in Mp708 plants. Furthermore, exogenous application of OPDA on maize jasmonic acid-deficient plants caused enhanced callose accumulation and heightened resistance to CLA, suggesting that the OPDA-mediated resistance to CLA is independent of the jasmonic acid pathway. We further demonstrate that the signaling function of OPDA, rather than a direct toxic effect, contributes to enhanced CLA resistance in Mp708.

Comparative transcriptome analysis reveals differential gene expression in resistant and susceptible tobacco cultivars in response to infection by cucumber mosaic virus

Cucumber mosaic virus (CMV) is one of the most severe viral diseases transmitted by aphids infecting Solanum crops in China, causing great losses of crop yields and income in rural communities. The tobacco cultivars NC82 and Taiyan 8 are closely related but differ in resistance to CMV. NC82 is susceptible to infection and Taiyan 8 is resistant, but the mechanisms underlying this difference in resistance are not clear. In this study, we conducted RNA sequencing to analyze changes in gene expression induced in the leaves of Taiyan 8 and NC82 upon systemic infection with CMV, compared with gene expression in the leaves of mock-inoculated plants. Leaves were sampled at one, three, eight, and 15 days after infection. In total, 3443 and 747 differentially expressed genes were identified in Taiyan 8 and NC82, respectively. Gene ontology and pathway enrichment analyses revealed that the different responses to CMV infection between cultivars were based on microtubule-based processes, pentose and glucuronate interconversions, plant–pathogen interaction, and hormone signal transduction pathways. Genes encoding pathogenesis-related proteins, disease-resistance proteins, lipoxygenase, cellulose synthase, an auxin response factor, and an ethylene receptor showed different expression patterns. The differences in gene expression following CMV infection likely contributed to the different resistance levels of these two tobacco cultivars. The comprehensive transcriptome dataset described here, which includes candidate response genes, will serve as a resource for further studies of the molecular mechanisms associated with tobacco defense responses against CMV.

Waterlogging-induced adventitious root formation in cucumber is regulated by ethylene and auxin through reactive oxygen species signalling.

Development of adventitious roots (ARs) at the base of the shoot is an important adaptation of plants to waterlogging stress; however, its physiological mechanisms remain unclear. Here, we investigated the regulation of AR formation under waterlogged conditions by hormones and reactive oxygen species (ROS) in Cucumis sativus L., an agriculturally and economically important crop in China. We found that ethylene, auxin, and ROS accumulated in the waterlogged cucumber plants. On the other hand, application of the ethylene receptor inhibitor 1-methylcyclopropene (1-MCP), the auxin transport inhibitor 1-naphthylphthalamic acid (NPA), or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) decreased the number of ARs induced by waterlogging. Auxin enhanced the expression of ethylene biosynthesis genes, which led to ethylene entrapment in waterlogged plants. Both ethylene and auxin induced the generation of ROS. Auxin-induced AR formation was inhibited by 1-MCP, although ethylene-induced AR formation was not inhibited by NPA. Both ethylene- and auxin-induced AR formation were counteracted by DPI. These results indicate that auxin-induced AR formation is dependent on ethylene, whereas ethylene-induced AR formation is independent of auxin. They also show that ROS signals mediate both ethylene- and auxin-induced AR formation in cucumber plants.