Ethylene Induction Research Articles

Unveiling the unique aroma of Morus macroura through integrated volatile metabolome and transcriptome analysis

Mulberries, especially the ‘BaiChang’ (Morus macroura) variety known for its creamy flavour, are highly valued by consumers and the market for their high nutritional value and unique aroma. However, the formation mechanism of its unique aroma compounds remains unclear. This study employed a combination of volatile metabolomics and transcriptomics analyses to examine volatile organic compounds (VOCs) and transcriptional changes at different developmental stages of ‘BaiChang’ mulberries. A total of 663 VOCs were identified, with 342 of annotated with different odours. Differential analysis revealed that the three comparison groups shared 56 differential metabolites, and each group contained 35, 56 and 17 unique differential metabolites. Among them, the 69 differential metabolites related to sweet, waxy, coconut and oil were screened. The content of 2(3H)-furanone, 5-hexyldihydro drastically increased during the S3 stage, and its aroma characteristics are consistent with the sensory phenotype. Among these, γ-decalactone is inferred to be the key VOC in ‘BaiChang’ mulberries. By integrating transcriptome data, 13 key structural genes were identified as potentially related to the synthesis of γ-decalactone, including CYPs, FAE, FAH, ACXs and EHLs. Most of these genes are highly expressed during the later stages of fruit development. Additionally, a preliminary dynamic relationship between lactones and esters was inferred during the development of ‘BaiChang’ mulberries. Furthermore, by combining weighted gene coexpression and K-means analyses, it was found that the biosynthesis of lactones and esters may be regulated by ethylene induction and transcription factors such as MYB, NAC, MDDS and bZIP. This study lays the foundation for understanding of the regulatory mechanisms underlying the formation of the unique aroma of ‘BaiChang’ mulberries and provides new insights for the further exploration of superior mulberry varieties.

Study on the expression regulation of the CTR1 gene in the ethylene signaling pathway

The CONSTITUTIVE TRIPLERESPONSE1 (CTR1) is a crucial component in the ethylene signaling pathway. CTR1 transmits signals perceived by ethylene receptors to downstream EIN2 proteins through phosphorylation/dephosphorylation. Although some studies have explored the functions and mechanisms of CTR1, research on its expression and regulation remains relatively limited. This study investigates the tissue-specific expression of the Arabidopsis CTR1 gene and its expression and regulatory mechanisms under ethylene induction. Arabidopsis was treated with ethylene, and changes in CTR1 gene expression were detected using real-time quantitative PCR. The experimental results show that in rosette leaves of 28-day-old Arabidopsis, CTR1 expression is induced by ethylene. To investigate its molecular mechanism, the promoter sequence of the CTR1 was cloned and vectors were constructed by linking the promoter sequence with luciferase and GUS genes. Stable transgenic Arabidopsis lines were obtained, and promoter activity in these materials was analyzed. Promoter activity analysis confirmed that CTR1 promoter activity is ethylene-inducible and that this induction is dependent on the functions of proteins such as EIN2, EIN3, and EILs. Additionally, the study found that CTR1 expression is higher during seed germination and maintained at lower levels in mature leaves and plants. This study provides a detailed observation of CTR1 gene expression and, for the first time, identifies that the CTR1 promoter is regulated by ethylene induction, offering new options for designing ethylene signaling pathway reporter systems.

Effective biological control of chickpea rabies (Ascochyta rabiei) through systemic phytochemical defenses activation by Trichoderma roots colonization: From strain characterization to seed coating

Chickpea (Cicer arietinum) is a legume of great economic and agricultural importance worldwide, whose crop is severely affected by rust or Ascochyta blight, caused by the fungus Ascochyta rabiei. The fungal genus Trichoderma includes several species widely characterized as effective biological control agents against crop pathogens. First, this work characterized several species of the genus Trichoderma as potential biological control agents of A. rabiei directly (in vitro confrontation) or indirectly in chickpea plants (activation of systemic resistance), selecting T. harzianum EN1 as the most efficient strain. Subsequently, different materials were tested as coatings to apply the T. harzianum conidia on chickpea seeds, determining that gum arabic at 1 % concentration was the one that most promoted the germination of conidia and seeds. The third phase of the study was based on the application of the coating and T. harzianum conidia on chickpea seeds and to study plant survival after infection with the pathogen A. rabiei, characterizing root colonization by Trichoderma and systemic hormonal and metabolic changes related to the induction of systemic defenses. The treatment of chickpea seeds with gum arabic and T. harzianum conidia was found to increase Trichoderma-root colonization and to improve plant survival. The induction of systemic ethylene- and melatonin-mediated resistance, which led to the accumulation of nicotinic acid in plant tissues, was considered the cause of such a protection. Therefore, T. harzianum applied as seed coating with gum arabic could be a good biological control strategy against A. rabiei on chickpea, due to the induction of systemic resistance.

Genome-wide identification of PEBP gene family in pineapple reveal its potential functions in flowering.

Phosphatidylethanolamine binding protein (PEBP) plays an important role in regulating flowering time and morphogenesis of plants. However, the identification and functional analysis of PEBP gene in pineapple (AcPEBP) have not been systematically studied. The pineapple genome contained 11 PEBP family members, which were subsequently classified into three subfamilies (FT-like, TFL-like and MFT-like) based on phylogenetic relationships. The arrangement of these 11 shows an unequal pattern across the six chromosomes of pineapple the pineapple genome. The anticipated outcomes of the promoter cis-acting elements indicate that the PEBP gene is subject to regulation by diverse light signals and endogenous hormones such as ethylene. The findings from transcriptome examination and quantitative real-time polymerase chain reaction (qRT-PCR) indicate that FT-like members AcFT3 and AcFT4 display a heightened expression level, specifically within the floral structures. The expression of AcFT3 and AcFT4 increases sharply and remains at a high level after 4 days of ethylene induction, while the expression of AcFT7 and AcMFT1 decreases gradually during the flowering process. Additionally, AcFT3, AcFT4 and AcFT7 show specific expression in different floral organs of pineapple. These outcomes imply that members belonging to the FT-like subfamily may have a significant impact on the process of bud differentiation and flower development. Through transcriptional activation analysis, it was determined that AcFT4 possesses transcriptional activation capability and is situated in the nucleus and peripheral cytoplasm. Overexpression of AcFT4 in Arabidopsis resulted in the promotion of early flowering by 6-7 days. The protein interaction prediction network identified potential flower regulators, including CO, AP1, LFY and SOC1, that may interact with PEBP proteins. This study explores flower development in pineapple, thereby serving as a valuable reference for future research endeavors in this domain.

Promotive effects of endophytic rhizobacteria on tiller and root growth in creeping bentgrass during drought stress and post‐stress recovery involving regulation of hormone and sugar metabolism

AbstractStress‐induced accumulation of ethylene exacerbates drought damages in plants and suppressing stress induction of ethylene may promote plant tolerance to drought stress. The objective of this study was to investigate the effects of endophytic bacteria (Paraburkholderia aspalathi) with 1‐aminocyclopropane‐1‐carboxylic acid (ACC) deaminase enzymes in suppressing ethylene production on plant tolerance to drought stress and post‐stress recovery and the underlying physiological mechanisms of P. aspalathi‐regulation in creeping bentgrass (Agrostis stolonifera L.). A novel strain of P. aspalathi, "WSF23," with ACC deaminase activity was used to inoculate the roots of creeping bentgrass plants (cv. "Penncross") subjected to drought stress for 35 days and rewatered for 15 days (post‐stress recovery) in controlled‐environment growth chambers. Inoculation with WSF23 bacteria resulted in an increased number of tillers, tillering production rate, root viability, and root growth (quantified in length, surface area, volume, and dry weight) during drought stress or rewatering. Inoculation of plants with WSF23 bacteria increased cytokinin (CK) (c‐Zeatin and tZ‐riboside) and jasmonate (JA‐Ile) content and reduced ACC and abscisic acid (ABA) content in roots during drought or rewatering. Sugar accumulation in crowns was promoted by inoculation during drought stress. The differential changes in ACC, CK, ABA, and JA‐Ile and sugar accumulation due to the bacterial inoculation could contribute to ACC deamination bacteria‐improved drought tolerance and post‐stress recovery in terms of tiller production and root proliferation and elongation in creeping bentgrass.

Protein Kinase RhCIPK6 Promotes Petal Senescence in Response to Ethylene in Rose (Rosa Hybrida).

Cultivated roses have the largest global market share among ornamental crops. Postharvest release of ethylene is the main cause of accelerated senescence and decline in rose flower quality. To understand the molecular mechanism of ethylene-induced rose petal senescence, we analyzed the transcriptome of rose petals during natural senescence as well as with ethylene treatment. A large number of differentially expressed genes (DEGs) were observed between developmental senescence and the ethylene-induced process. We identified 1207 upregulated genes in the ethylene-induced senescence process, including 82 transcription factors and 48 protein kinases. Gene Ontology enrichment analysis showed that ethylene-induced senescence was closely related to stress, dehydration, and redox reactions. We identified a calcineurin B-like protein (CBL) interacting protein kinase (CIPK) family gene in Rosa hybrida, RhCIPK6, that was regulated by age and ethylene induction. Reducing RhCIPK6 expression through virus-induced gene silencing significantly delayed petal senescence, indicating that RhCIPK6 mediates petal senescence. In the RhCIPK6-silenced petals, several senescence associated genes (SAGs) and transcription factor genes were downregulated compared with controls. We also determined that RhCIPK6 directly binds calcineurin B-like protein 3 (RhCBL3). Our work thus offers new insights into the function of CIPKs in petal senescence and provides a genetic resource for extending rose vase life.

Rice EIL1 interacts with OsIAAs to regulate auxin biosynthesis mediated by the tryptophan aminotransferase MHZ10/OsTAR2 during root ethylene responses.

Ethylene plays essential roles in adaptive growth of rice (Oryza sativa). Understanding of the crosstalk between ethylene and auxin (Aux) is limited in rice. Here, from an analysis of the root-specific ethylene-insensitive rice mutant mao hu zi 10 (mhz10), we identified the tryptophan aminotransferase (TAR) MHZ10/OsTAR2, which catalyzes the key step in indole-3-pyruvic acid-dependent Aux biosynthesis. Genetically, OsTAR2 acts downstream of ethylene signaling in root ethylene responses. ETHYLENE INSENSITIVE3 like1 (OsEIL1) directly activated OsTAR2 expression. Surprisingly, ethylene induction of OsTAR2 expression still required the Aux pathway. We also show that Os indole-3-acetic acid (IAA)1/9 and OsIAA21/31 physically interact with OsEIL1 and show promotive and repressive effects on OsEIL1-activated OsTAR2 promoter activity, respectively. These effects likely depend on their EAR motif-mediated histone acetylation/deacetylation modification. The special promoting activity of OsIAA1/9 on OsEIL1 may require both the EAR motifs and the flanking sequences for recruitment of histone acetyltransferase. The repressors OsIAA21/31 exhibit earlier degradation upon ethylene treatment than the activators OsIAA1/9 in a TIR1/AFB-dependent manner, allowing OsEIL1 activation by activators OsIAA1/9 for OsTAR2 expression and signal amplification. This study reveals a positive feedback regulation of ethylene signaling by Aux biosynthesis and highlights the crosstalk between ethylene and Aux pathways at a previously underappreciated level for root growth regulation in rice.

Transcriptomic analysis provides insights into the AUXIN RESPONSE FACTOR 6-mediated repression of nicotine biosynthesis in tobacco (Nicotiana tabacum L.).

NtARF6 overexpression represses nicotine biosynthesis in tobacco. Transcriptome analysis suggests that NtARF6 acts as a regulatory hub that connect different phytohormone signaling pathways to antagonize the jasmonic acid-induced nicotine biosynthesis. Plant specialized metabolic pathways are regulated by a plethora of molecular regulators that form complex networks. In Nicotiana tabacum, nicotine biosynthesis is regulated by transcriptional activators, such as NtMYC2 and the NIC2-locus ERFs. However, the underlying molecular mechanism of the regulatory feedback is largely unknown. Previous research has shown that NbARF1, a nicotine synthesis repressor, reduces nicotine accumulation in N. benthamiana. In this study, we demonstrated that overexpression of NtARF6, an ortholog of NbARF1, was able to reduce pyridine alkaloid accumulation in tobacco. We found that NtARF6 could not directly repress the transcriptional activities of the key nicotine pathway structural gene promoters. Transcriptomic analysis suggested that this NtARF6-induced deactivation of alkaloid biosynthesis might be achieved by the antagonistic effect between jasmonic acid (JA) and other plant hormone signaling pathways, such as ethylene (ETH), salicylic acid (SA), abscisic acid (ABA). The repression of JA biosynthesis is accompanied by the induction of ETH, ABA, and SA signaling and pathogenic infection defensive responses, resulting in counteracting JA-induced metabolic reprogramming and decreasing the expression of nicotine biosynthetic genes in vivo. This study provides transcriptomic evidence for the regulatory mechanism of the NtARF6-mediated repression of alkaloid biosynthesis and indicates that this ARF transcription factor might act as a regulatory hub to connect different hormone signaling pathways in tobacco.

Ethylene response factors regulate expression of HbSUT3, the sucrose influx carrier in laticifers of Hevea brasiliensis.

Natural rubber is an important industrial raw material and is commercially produced by rubber trees (Hevea brasiliensis). The sucrose transporter HbSUT3 plays an essential role in rubber production. Its expression in latex (cytoplasm of rubber-producing laticifers) is induced by bark treatment with Ethrel, an ethylene releaser, and the inducing effect correlates well with Ethrel-stimulated rubber yield increase. However, the mechanisms of ethylene induction on HbSUT3 expression are not known. Here, five Ethylene Response Factor (ERF) genes were identified from the cDNA library of Hevea latex by yeast one-hybrid screening with the promoter of HbSUT3 gene as bait. As revealed in a tobacco (Nicotiana tabacum) protoplast transient expression system, these HbERFs were mainly localized in the nucleus and four of them exhibited apparent transactivation activity. Of the five HbERF genes, HbERF-IXc4 was the most frequently screened in yeast one-hybrid, accounting for 65% of the ERF clones obtained. Moreover, among the five HbERFs, HbERF-IXc4 showed the strongest transactivation capacity when expressed in tobacco protoplast, the highest transcript abundance in latex and a close expressional correlation with its target gene, HbSUT3, in response to the Ethrel treatment. Taken together, our results indicate that ERFs, especially HbERF-IXc4, are critically involved in the activation of HbSUT3 expression in latex after Ethrel treatment on Hevea bark, and thus the stimulated latex yield.

CRISPR/Cas9-mediated genome editing of MaACO1 (aminocyclopropane-1-carboxylate oxidase 1) promotes the shelf life of banana fruit.

Banana is a fruit with high nutrient content and high economic importance. It is regarded as a main staple food in developing countries. As a typical climacteric fruit, banana will ripen and decay in one week after exogenous ethylene induction. The short shelf life of banana largely limits its storage, transportation and marketing, and causes great post-harvest loss (Krishnakumar, T. and Thirupathi, V. 2014). The shelf life of banana is closely related to ethylene production, which is the first factor considered for developing postharvest preservation technology.

Exogenous spermidine improves salt tolerance of pecan-grafted seedlings via activating antioxidant system and inhibiting the enhancement of Na+/K+ ratio

Salt stress is abiotic stress that negatively impacts plant growth. Exogenous spermidine (SPD) has been proposed as a priming agent that effectively alleviates various abiotic stresses in plants. To evaluate the alleviation role of exogenous SPD application against salt stress, we studied the physiological and biochemical changes, and the expression of gene encoding antioxidant enzymes and phytohormones in the SPD-treated pecan-grafted seedling. The results revealed that for the seedlings growing under salt stress environment, a drop in the total chlorophyll content and photosynthetic capability was observed. These effects subsided when the seedlings were treated with SPD. Moreover, the malondialdehyde level and Na⁺/K⁺ ratio, as well as the damage of the chloroplast ultrastructure in the seedlings, were markedly suppressed after SPD treatment. Compared with the non-SPD-treated counterparts, the exogenous SPD application promoted higher antioxidant enzyme activities and their corresponding gene expression. At the same time, the induction of abscisic acid and ethylene was suppressed. The results indicate that the exogenous SPD plays a vital role in alleviating salt-incurred phytotoxicity and oxidative damage in pecan-grafted seedlings. The remissive role of exogenous SPD is implicated by its interplay with the expression of the antioxidant enzymes and phytohormones in the pecan-grafted seedlings.

Brassinosteroids Induce Strong, Dose-Dependent Inhibition of Etiolated Pea Seedling Growth Correlated with Ethylene Production.

We have recently discovered that brassinosteroids (BRs) can inhibit the growth of etiolated pea seedlings dose-dependently in a similar manner to the ‘triple response’ induced by ethylene. We demonstrate here that the growth inhibition of etiolated pea shoots strongly correlates with increases in ethylene production, which also responds dose-dependently to applied BRs. We assessed the biological activities of two natural BRs on pea seedlings, which are excellent material as they grow rapidly, and respond both linearly and uni-phasically to applied BRs. We then compared the BRs’ inhibitory effects on growth, and induction of ethylene and ACC (1-aminocyclopropane-1-carboxylic acid) production, to those of representatives of other phytohormone classes (cytokinins, auxins, and gibberellins). Auxin induced ca. 50-fold weaker responses in etiolated pea seedlings than brassinolide, and the other phytohormones induced much weaker (or opposite) responses. Following the optimization of conditions for determining ethylene production after BR treatment, we found a positive correlation between BR bioactivity and ethylene production. Finally, we optimized conditions for pea growth responses and developed a new, highly sensitive, and convenient bioassay for BR activity.

A polerovirus, Potato leafroll virus, alters plant-vector interactions using three viral proteins.

Potato leafroll virus (PLRV), genus Polerovirus, family Luteoviridae, is a major pathogen of potato worldwide. PLRV is transmitted among host plants by aphids in a circulative-nonpropagative manner. Previous studies have demonstrated that PLRV infection increases aphid fecundity on, and attraction to, infected plants as compared to controls. However, the molecular mechanisms mediating this relationship are still poorly understood. In this study, we measured the impact of PLRV infection on plant-aphid interactions and plant chemistry in two hosts: Solanum tuberosum and Nicotiana benthamiana. Our study demonstrates that PLRV infection attenuates the induction of aphid-induced jasmonic acid and ethylene in S. tuberosum and N. benthamiana. Using transient expression experiments, insect bioassays and chemical analysis, we show that expression of three PLRV proteins (P0, P1, and P7) mediate changes in plant-aphid interactions and inhibition of aphid-induced jasmonic acid and ethylene in N. benthamiana. This study enhances our understanding of the plant-vector-pathogen interface by elucidating new mechanisms by which plant viruses transmitted in a circulative manner can manipulate plant hosts.

Red to Brown: An Elevated Anthocyanic Response in Apple Drives Ethylene to Advance Maturity and Fruit Flesh Browning.

The elevation of anthocyanin contents in fruits and vegetables is a breeding target for many crops. In some fruit, such as tomato, higher anthocyanin concentrations enhance storage and shelf life. In contrast, highly anthocyanic red-fleshed apples (Malus x domestica) have an increased incidence of internal browning flesh disorder (IBFD). To determine the mechanisms underlying this, ‘Royal Gala’ cultivar apples over-expressing the anthocyanin-related transcription factor (TF) MYB10 (35S:MYB10), which produces fruit with highly pigmented flesh, were compared with standard ‘Royal Gala’ Wild Type (WT) grown under the same conditions. We saw no incidence of IBFD in WT ‘Royal Gala’ but the over-expression of MYB10 in the same genetic background resulted in a high rate of IBDF. We assessed concentrations of potential substrates for IBDF and a comparison of metabolites in these apples showed that anthocyanins, chlorogenic acid, pro-cyanidins, flavon-3-ols, and quercetin were all higher in the MYB10 lines. For the flavol-3-ols sub-group, epicatechin rather than catechin was elevated in MYB10 lines compared with the control fruit. Internal ethylene concentrations were measured throughout fruit development and were significantly higher in 35S:MYB10 lines, and ethylene was detected at an earlier developmental stage pre-harvest. Expression analysis of key genes associated with ethylene biosynthesis (aminocyclopropane-1-carboxylic acid synthase and oxidase; ACS and ACO) and polyphenol oxidase (PPO) showed the potential for increased ethylene production and the mechanism for enhanced PPO-mediated browning. The expression of a transcription factor of the ethylene response factor (ERF) class, ERF106, was elevated in red flesh. Analysis of transcriptional activation by MYB10 showed that this transcription factor could activate the expression of apple ACS, ACO, and ERF106 genes. Our data show a link between the elevation of anthocyanin-related transcription factors and an undesirable fruit disorder. The accelerated advancement of maturity via premature ethylene induction has implications for the breeding and storage of these more highly pigmented plant products.

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.

Induction of ethylene inhibits development of soybean sudden death syndrome by inducing defense-related genes and reducing Fusarium virguliforme growth.

Ethylene is a gaseous hormone that regulates plant responses to biotic and abiotic stresses. To investigate the importance of ethylene in soybean resistance to Fusarium virguliforme (Fv), the causal agent of sudden death syndrome (SDS), soybean cultivars Williams 82 (SDS-susceptible) and MN1606 (SDS-resistant) were treated 24 h before and 24h after Fv inoculation with either ethephon (ethylene inducer), cobalt chloride (ethylene biosynthesis inhibitor), or 1-MCP (ethylene perception inhibitor). Inoculated plants were grown for 21 days at 24°C in the greenhouse and then evaluated for SDS severity and expression of soybean defense genes. In both cultivars, plants treated with ethephon showed lower SDS foliar severity compared to the other treatments, whereas those treated with cobalt chloride or 1-MCP showed the same or higher SDS foliar severity compared to the water-treated control. Ethephon application resulted in activation of genes involved in ethylene biosynthesis, such as ethylene synthase (ACS) and ethylene oxidase (ACO), and genes involved in soybean defense response, such as pathogenesis-related protein (PR), basic peroxidase (IPER), chalcone synthase (CHS), and defense-associated transcription factors. Cobalt chloride and 1-MCP treatments had little or no effect on the expression of these genes. In addition, ethephon had a direct inhibitory effect on in-vitro growth of Fv on PDA media. Our results suggest that ethephon application inhibits SDS development directly by slowing Fv growth and/or by inducing soybean ethylene signaling and the expression of defense related genes.

The Phytophthora sojae RXLR effector Avh238 destabilizes soybean Type2 GmACSs to suppress ethylene biosynthesis and promote infection.

Phytophthora pathogens secrete many effector proteins to manipulate host innate immunity. PsAvh238 is a Phytophthora sojae N-terminal Arg-X-Leu-Arg (RXLR) effector, which evolved to escape host recognition by mutating one nucleotide while retaining plant immunity-suppressing activity to enhance infection. However, the molecular basis of the PsAvh238 virulence function remains largely enigmatic. By using coimmunoprecipitation and liquid chromatography-tandem mass spectrometry analysis, we identified the 1-aminocyclopropane-1-carboxylate synthase (ACS) isoforms, the key enzymes in ethylene (ET) biosynthesis, as a host target of PsAvh238. We show that PsAvh238 interacts with soybean ACSs (GmACSs) invivo and invitro. By destabilizing Type2 GmACSs, PsAvh238 suppresses Type2 ACS-catalyzed ET biosynthesis and facilitates Phytophthora infection. Silencing of Type2 GmACSs, and inhibition of ET biosynthesis or signaling, increase soybean susceptibility to P.sojae infection, supporting a role for Type2 GmACSs and ET in plant immunity against P.sojae. Moreover, wild-type P.sojae but not the PsAvh238-disrupted mutants, inhibits ET induction and promotes P.sojae infection in soybean. Our results highlight the ET biosynthesis pathway as an essential part in plant immunity against P.sojae and a direct effector target.

Microbial pathway for anaerobic 5′-methylthioadenosine metabolism coupled to ethylene formation

Numerous cellular processes involving S-adenosyl-l-methionine result in the formation of the toxic by-product, 5'-methylthioadenosine (MTA). To prevent inhibitory MTA accumulation and retain biologically available sulfur, most organisms possess the "universal" methionine salvage pathway (MSP). However, the universal MSP is inherently aerobic due to a requirement of molecular oxygen for one of the key enzymes. Here, we report the presence of an exclusively anaerobic MSP that couples MTA metabolism to ethylene formation in the phototrophic bacteria Rhodospirillum rubrum and Rhodopseudomonas palustris In vivo metabolite analysis of gene deletion strains demonstrated that this anaerobic MSP functions via sequential action of MTA phosphorylase (MtnP), 5-(methylthio)ribose-1-phosphate isomerase (MtnA), and an annotated class II aldolase-like protein (Ald2) to form 2-(methylthio)acetaldehyde as an intermediate. 2-(Methylthio)acetaldehyde is reduced to 2-(methylthio)ethanol, which is further metabolized as a usable organic sulfur source, generating stoichiometric amounts of ethylene in the process. Ethylene induction experiments using 2-(methylthio)ethanol versus sulfate as sulfur sources further indicate anaerobic ethylene production from 2-(methylthio)ethanol requires protein synthesis and that this process is regulated. Finally, phylogenetic analysis reveals that the genes corresponding to these enzymes, and presumably the pathway, are widespread among anaerobic and facultatively anaerobic bacteria from soil and freshwater environments. These results not only establish the existence of a functional, exclusively anaerobic MSP, but they also suggest a possible route by which ethylene is produced by microbes in anoxic environments.

Pleiotropic effects of CmACS7 on fruit growth and quality parameters in melon (Cucumis melo)

CmACS7 is a sex determination gene that is known to be involved in the biosynthesis of ethylene at very early stages of pistillate flower development in melon, promoting so the arrest of stamen during the development of female flowers, and resulting in monoecious plants. Loss-of-function mutations for CmACS7 reduce the production of ethylene in pistillate flowers, which results in hermaphrodite flowers and andromonoecious plants. In this paper we compare fruit growth and quality in monoecious and andromonoecious isogenic lines of five different genotypes of 'Galia' (Cucumis melo var. reticulatus) and 'Cantaloupe' (Cucumis melo var. cantalupensis) melons. The gene not only regulates sex determination but also other fruit growth parameters. The mutation that caused andromonoecy and reduced ethylene in female flowers promoted a reduction in fruit set, fruit weight and number of total and viable seeds, as well as an alteration of fruit shape in the five genotypes analyzed. In some genotypes monoecy stability was reduced, concomitantly with a loss of significant differences between isogenic lines. The gene mutation, however, had no effect on fruit quality parameters such as total soluble solids, fruit pH and titratable acidity. To assess whether these pleiotropic effects of the gene are associated with ethylene biosynthesis, we analyzed production of ethylene in the ovary/fruit of unpollinated flowers during the days immediately after anthesis, confirming a higher induction of ethylene in the monoecious isoline. Results are discussed in relation to ethylene production and autoregulation of ethylene biosynthesis in flowers and fruits.

Differential expression of defense-related genes in chilli pepper infected with anthracnose pathogen Colletotrichum truncatum

Anthracnose disease caused by Colletotrichum truncatum is a major economic constraint to chilli production in the tropical and subtropical regions of the world including India. To understand the molecular mechanisms of defense against anthracnose, we used a differential chilli-C. truncatum system consisting of two cultivars of chilli (Susceptible; Teja Jhal, TJ and resistant; Bhut Jolokia, BJ) and a highly virulent C. truncatum isolate to evaluate the temporal expression of seventeen defense-related genes associated with multiple defense signaling pathways. Quantitative real time PCR demonstrated rapid induction and significant accumulation of jasmonic acid (JA) and ethylene (ET) responsive genes such as plant defensin 1.2, Lypoxygenase 3, Allene oxide synthase and ACC synthase 2 in the resistant cultivar post treatment with C. truncatum. Significant induction of these genes was also realized upon exogenous treatment with JA and ET. The salicylic acid (SA) responsive phenylalanine ammonia-lyase 2 gene was upregulated only under incompatible interaction. Further, the transcript levels of pathogenesis related proteins PR2 and PR5 was significantly higher in the resistant genotype whereas PR1 and PR3 were moderately responsive. In addition, the expression of defense responsive transcription factors increased gradually in the resistant cultivar and remained significantly higher at 9 dpi as opposed to the susceptible one. Combined result analyses revealed that chilli adopts multiple defense strategies in mediating defence responses against the C. truncatum infection. Overall, this work represents a valuable resource for future functional genomics experiments to unravel the molecular mechanisms of host resistance and pathogen virulence in the agriculturally important chilli-C. truncatum pathosystem.