Control of Peach Leaf Curl with Foliar Applications of Plant Immunity Inducers and Insights in Elicitation of Defense Responses against Taphrina deformans.

Taphrina deformans is the causal agent of leaf curl, a serious peach disease which causes significant losses in peach production worldwide. Nowadays, in order to control plant diseases, it is necessary to adopt novel and low-cost alternatives to conventional chemical fungicides. These promising strategies are targeted at eliciting host defense mechanisms via priming the host through the consecutive application of plant immunity inducers prior to pathogen challenge. In this study, we investigated whether chitosan or yeast cell wall extracts could provide enhanced tolerance against leaf curl in two-season field trials. Furthermore, we addressed the possible molecular mechanisms involved beyond the priming of immune responses by monitoring the induction of key defense-related genes. The efficacy of spraying treatments against peach leaf curl with both inducers was significantly higher compared to the untreated control, showing efficacy in reducing disease severity of up to 62.6% and 73.9% for chitosan and yeast cell wall extracts, respectively. The application of chitosan in combination with copper hydroxide was more efficient in reducing disease incidence and severity, showing efficacy values in the range of 79.5-93.18%. Peach plantlets were also spray-treated with immunity inducers three times prior to leaf inoculation with T. deformans blastospores in their yeast phase. The relative expression levels of nine key defense and priming genes, including those encoding members of pathogenesis-related (PR) proteins and hub genes associated with hormone biosynthesis, were monitored by RT-qPCR across three days after inoculation (dai). The results indicate that pre-treatments with these plant immunity inducers activated the induction of genes involved in salicylic acid (SA) and jasmonate (JA) defense signaling pathways that may offer systemic resistance, coupled with the upregulation of genes conferring direct antimicrobial effects. Our experiments suggest that these two plant immunity inducers could constitute useful components towards the effective control of T. deformans in peach crops.

Insights into the Transcriptional Reprogramming of Peach Leaves Inoculated with Taphrina deformans.

The dimorphic fungus Taphrina deformans is the causal agent of peach leaf curl disease, which affects leaves, flowers, and fruits. An RNA-seq approach was employed to gain insights into the transcriptional reprogramming of a peach cultivar during leaf inoculation with the yeast phase of the fungus across a compatible interaction. The results uncovered modulations of specific peach differentially expressed genes (DEGs) in peaches and pathways related to either the induction of host defense responses or pathogen colonization and disease spread. Expression profiles of DEGs were shown to be highly time-dependent and related to the presence of the two forms of the fungal growth, the inoculated yeast form and the later biotrophic phase during mycelial development. In parallel, this differential reprogramming was consistent with a diphasic detection of fungal load in the challenged leaves over the 120 h after inoculation (HAI) period. Leaf defense responses either occurred during the early yeast phase inoculation at 24 HAI, mediated primarily by cell wall modification processes, or more pronouncedly during the biotrophic phase at 72 HAI, as revealed by the activation of DEGs related to pathogen perception, signaling transduction, and secondary metabolism towards restraining further hypha proliferation. On the contrary, the expression patterns of specific DEGs at 120 HAI might further contribute to host susceptibility. These findings will further allow us to elucidate the molecular responses beyond the peach-T. deformans interaction.

Evaluation of Biological Plant Protection Products for Their Ability to Induce Olive Innate Immune Mechanisms and Control Colletotrichum acutatum, the Causal Agent of Olive Anthracnose.

Olive anthracnose is the most important fungal disease of the olive fruit worldwide, with the fungus Colletotrichum acutatum as the main cause of the disease in Greece. A total of 11 commercial biological plant protection products (bioPPPs) (Amylo-X®, Botector®, FytoSave®, LBG 01F34®, Mevalone®, Polyversum®, Remedier®, Serenade® ASO, Sonata®, Trianum-P®, Vacciplant®), with various modes of action against the fungus C. acutatum, were evaluated by bioassays using detached fruits of two important olive Greek varieties, cv. Koroneiki and cv. Kalamon. Subsequently, the most effective bioPPPs were evaluated for their ability to induce plant defense mechanisms, by determining the expression levels of ten Olea europaea defense genes (Pal, CuaO, Aldh1, Bglu, Mpol, Lox, Phely, CHI-2, PR-10, PR-5). Remedier®, Trianum-P®, Serenade® ASO, Sonata®, and Mevalone® were the most effective in reducing disease severity, and/or inhibiting the conidia production by the fungus at high rates. Post bioPPPs application, high expression levels of several olive plant defense genes were observed. This study provides insights into commercial bioPPPs' effectiveness in controlling olive anthracnose, as well as biocontrol-agents-mediated modulation of olive defense mechanisms.

Comparative transcriptome profiling and co-expression network analysis uncover the key genes associated with pear petal defense responses against Monilinia laxa infection.

Pear brown rot and blossom blight caused by Monilinia laxa seriously affect pear production worldwide. Here, we compared the transcriptomic profiles of petals after inoculation with M. laxa using two pear cultivars with different levels of sensitivity to disease (Sissy, a relatively tolerant cultivar, and Kristalli, a highly susceptible cultivar). Physiological indexes were also monitored in the petals of both cultivars at 2 h and 48 h after infection (2 HAI and 48 HAI). RNA-seq data and weighted gene co-expression network analysis (WGCNA) allowed the identification of key genes and pathways involved in immune- and defense-related responses that were specific for each cultivar in a time-dependent manner. In particular, in the Kristalli cultivar, a significant transcriptome reprogramming occurred early at 2 HAI and was accompanied either by suppression of key differentially expressed genes (DEGs) involved in the modulation of any defense responses or by activation of DEGs acting as sensitivity factors promoting susceptibility. In contrast to the considerably high number of DEGs induced early in the Kristalli cultivar, upregulation of specific DEGs involved in pathogen perception and signal transduction, biosynthesis of secondary and primary metabolism, and other defense-related responses was delayed in the Sissy cultivar, occurring at 48 HAI. The WGCNA highlighted one module that was significantly and highly correlated to the relatively tolerant cultivar. Six hub genes were identified within this module, including three WRKY transcription factor-encoding genes: WRKY 65 (pycom05g27470), WRKY 71 (pycom10g22220), and WRKY28 (pycom17g13130), which may play a crucial role in enhancing the tolerance of pear petals to M. laxa. Our results will provide insights into the interplay of the molecular mechanisms underlying immune responses of petals at the pear-M. laxa pathosystem.

Global Transcriptome Analysis of the Peach (Prunus persica) in the Interaction System of Fruit-Chitosan-Monilinia fructicola.

The peach (Prunus persica L.) is one of the most important stone-fruit crops worldwide. Nevertheless, successful peach fruit production is seriously reduced by losses due to Monilinia fructicola the causal agent of brown rot. Chitosan has a broad spectrum of antimicrobial properties and may also act as an elicitor that activate defense responses in plants. As little is known about the elicitation potential of chitosan in peach fruits and its impact at their transcriptional-level profiles, the aim of this study was to uncover using RNA-seq the induced responses regulated by the action of chitosan in fruit-chitosan-M. fructicola interaction. Samples were obtained from fruits treated with chitosan or inoculated with M. fructicola, as well from fruits pre-treated with chitosan and thereafter inoculated with the fungus. Chitosan was found to delay the postharvest decay of fruits, and expression profiles showed that its defense-priming effects were mainly evident after the pathogen challenge, driven particularly by modulations of differentially expressed genes (DEGs) related to cell-wall modifications, pathogen perception, and signal transduction, preventing the spread of fungus. In contrast, as the compatible interaction of fruits with M. fructicola was challenged, a shift towards defense responses was triggered with a delay, which was insufficient to limit fungal expansion, whereas DEGs involved in particular processes have facilitated early pathogen colonization. Physiological indicators of peach fruits were also measured. Additionally, expression profiles of particular M. fructicola genes highlight the direct antimicrobial activity of chitosan against the fungus. Overall, the results clarify the possible mechanisms of chitosan-mediated tolerance to M. fructicola and set new foundations for the potential employment of chitosan in the control of brown rot in peaches.

IoT for Monitoring Fungal Growth and Ochratoxin A Development in Grapes Solar Drying in Tunnel and in Open Air.

Optimisation of solar drying to reduce fungal growth and Ochratoxin A (OTA) contamination is a crucial concern in raisin and currant production. Stochastic and deterministic analysis has been utilized to investigate environmental indicators and drying characteristics. The analysis was performed using two seedless grape varieties (Crimson-red and Thompson-white) that were artificially inoculated with Aspergillus carbonarius during open-air and tunnel drying. Air temperature (T) and relative humidity (RH) were measured and analysed during the drying experiment, along with grape surface temperature (Ts), and water activity (aw). The grape moisture content, fungal colonization, and OTA contamination were estimated, along with the water diffusivity (Deff) and peel resistance (rpeel) to water transfer. Monitoring the surface temperature of grapes is essential in the early detection of fungal growth and OTA contamination. As surface temperature should be carried out continuously, remote sensing protocols, such as infrared sensors, provide the most efficient means to achieve this. Furthermore, data collection and analysis could be conducted through the Internet of Things (IoT), thereby enabling effortless accessibility. The average Ts of the grapes was 6.5% higher in the tunnel than in the open-air drying. The difference between the RH of air and that in the plastic crates was 16.26-17.22%. In terms of CFU/mL, comparison between white and red grapes in the 2020 and 2021 experiments showed that the red grapes exhibited significantly higher values than the white grapes. Specifically, the values for red grapes were 4.3 in 2021 to 3.4 times in 2020 higher compared to the white grapes. On the basis of the conducted analysis, it was concluded that tunnel drying provided some advantages over open-air drying, provided that hygienic and managerial requirements are met.

Environmental Conditions Affecting Ochratoxin A during Solar Drying of Grapes: The Case of Tunnel and Open Air-Drying.

Drying optimization, to mitigate fungal growth and Ochratoxin A (OTA) contamination is a key topic for raisin and currant production. Specific indicators of environmental conditions and drying properties were analyzed using two seedless grape varieties (Crimson-red and Thompson-white), artificially inoculated with Aspergillus carbonarius under open air and tunnel drying. The air temperature (T), relative humidity, grape surface temperature (Ts) and water activity throughout the drying experiment, the grapes' moisture content and the fungal colonization and OTA contamination during the drying process and their interactions were recorded and critically analyzed. Drying properties such as the water diffusivity (Deff) and peel resistance to water transfer were estimated. The grapes Ts was 5-7 °C higher in tunnel vs. open air-drying; the infected grapes had higher maximum Ts vs. the control (around 4-6 °C). OTA contamination was higher in tunnel vs. open air-dried grapes, but fungal colonies showed the opposite trend. The Deff was higher in tunnel than in the open air-drying by 54%; the infected grapes had more than 70% higher Deff than the control, differences explained by factors affecting the water transport. This study highlighted CFU and OTA indicators that affect the water availability between red and white grapes during open air and tunnel drying, estimated by the Deff and peel resistance. This raises new issues for future research.

Analysis of volatile emissions from grape berries infected with Aspergillus carbonarius using hyphenated and portable mass spectrometry.

Mycotoxins represent a serious risk for human and animal health. Οchratoxin A (OTA) is a carcinogenic mycotoxin produced by A. carbonarius that constitutes a severe problem for viticulture. In this study, we investigate the development of novel detection and on-line monitoring approaches for the detection of OTA in the field (i.e. out of the chemical laboratory) using advanced molecular sensing. Both stand-alone and hyphenated mass spectrometry (MS) based systems (e.g. Time-of-Flight ToF-MS and gas chromatography GC combined with MS) and compact portable membrane inlet MS (MIMS) have been employed for the first time to detect and monitor volatile emissions of grape berries infected by the fungus Aspergillus carbonarius. In vacuo (electron impact-EI) and ambient ionisation (electrospray ionisation-ESI) techniques were also examined. On-line measurements of the volatile emissions of grape berries, infected by various strains of A. carbonarius with different toxicity levels, were performed resulting in different olfactory chemical profiles with a common core of characteristic mass fragments, which could be eventually used for on-site detection and monitoring allowing consequent improvement in food security.

First Report of Colletotrichum acutatum Causing Anthracnose on Olives in Albania.

Olive trees (Olea europaea L.) are among the most important fruit tree crops grown in Albania, covering an estimated 8% of the arable land of this country. The highest amount of olive production in Albania is concentrated in the coastal districts of Fier, Berat, Elbasan, Lezha, Tirana, Kruja and Vlora, all with Mediterranean climate conditions. Anthracnose is the main disease of olive fruit caused by different Colletotrichum spp. primarily belonging to two complexes, C. acutatum sensu lato (s.l.) and C. gloeosporioides s.l. (Cacciola et al. 2012; Schena et al. 2014.). On July 2018, field observations of about 50 olive trees in the Ishull Shengjin Lezhe Region (54% prevalence), 1 km away from the coast showed severe symptoms of mummified olive fruits in about 20 to 40% disease incidence and 30% disease severity of the Italian table olive cv. Frantoio trees resulting in premature fruit drop or mummification. The causal agent was isolated directly from infected fruits on potato dextrose agar and Rose Bengal nutrient media. Microscopic examinations of five single spore isolated fungal colonies showed acervuli with typical conidia of the genus Colletotrichum that were aseptate, straight, hyaline, subcylindrical with rounded ends and 12.3 to 22.1 µm long (mean = 17.4 µm) and 2.5 to 7.3 µm wide (mean = 5.9 µm) (n= 50 conidia) (Damm et al. 2012). To identify the fungal species, DNA from two single-spore isolates (Col-3-ALB and Col-9-ALB) isolated from fruits was extracted, and six genes were amplified (ITS, GAPDH, CHS-1, HIS3, ACT, and TUB2) using the primers reviewed in Damm et al. (2012). PCR products were sequenced, and BLAST analysis showed 100% identity to C. acutatum for both isolates (GenBank accession nos. for Col-9-ALB MT218337 [ITS1-5.8-ITS2], MT274748 [CHS-1], MT274749 [HIS3], MT274750 [GAPDH], MT274751 [TUB2], and MT274752 [ACT]). Phylogenetic analysis using the concatenated sequences of Col-9-ALB, the type species of C. acutatum (112996), a previously identified published Greek C. acutatum isolate (O9) and three C. godetiae strains confirmed the identification of Col-9-ALB as C. acutatum. Pathogenicity tests were performed in the laboratory to confirm the ability of C. acutatum isolates to cause disease on olive drupes. Fruits were surface disinfected with 0.1% NaClO for 3 min and rinsed with ddH2O. Artificial inoculations with the two above isolates were performed by spraying 24 olive fruits per isolate cv. Kalamon (eight olive fruits per replication) with a spore suspension (106 conidia/ml). Olive fruits sprayed with sterilized water served as untreated control. After inoculation, olive fruits were placed in closed sterile plastic boxes and kept at 26°C with a 12-h photoperiod. First rot symptoms and formation of acervuli by the pathogen were initiated 3 days after inoculation. Eight days post-inoculation, all treatments exhibited typical anthracnose symptoms similar to those observed in olive orchards (extensive fruit rot). To fulfil Koch's postulates, C. acutatum was re-isolated from 10 random symptomatic olive fruits/isolate and their identity was confirmed from all samples. To our knowledge, this is the first report of C. acutatum causing fruit rot on olive trees in Albania. It is important to further study the epidemiology for the disease under local climate conditions and on different olive cultivars in order to develop effective management strategies for this very destructive disease of olive.

AFLA-PISTACHIO: Development of a Mechanistic Model to Predict the Aflatoxin Contamination of Pistachio Nuts.

In recent years, very many incidences of contamination with aflatoxin B1 (AFB1) in pistachio nuts have been reported as a major global problem for the crop. In Europe, legislation is in force and 12 µg/kg of AFB1 is the maximum limit set for pistachios to be subjected to physical treatment before human consumption. The goal of the current study was to develop a mechanistic, weather-driven model to predict Aspergillus flavus growth and the AFB1 contamination of pistachios on a daily basis from nut setting until harvest. The planned steps were to: (i) build a phenology model to predict the pistachio growth stages, (ii) develop a prototype model named AFLA-pistachio (model transfer from AFLA-maize), (iii) collect the meteorological and AFB1 contamination data from pistachio orchards, (iv) run the model and elaborate a probability function to estimate the likelihood of overcoming the legal limit, and (v) manage a preliminary validation. The internal validation of AFLA-pistachio indicated that 75% of the predictions were correct. In the external validation with an independent three-year dataset, 95.6% of the samples were correctly predicted. According to the results, AFLA-pistachio seems to be a reliable tool to follow the dynamic of AFB1 contamination risk throughout the pistachio growing season.

Corrigendum: Effective Biopesticides and Biostimulants to Reduce Aflatoxins in Maize Fields.

[This corrects the article DOI: 10.3389/fmicb.2019.02645.].

Effective Biopesticides and Biostimulants to Reduce Aflatoxins in Maize Fields.

The presence of ear rots in maize caused by Aspergillus flavus that are also associated with the production of aflatoxins has evolved into an increasing problem over the last few years. Since no commercial biological control products are still available to control A. flavus in maize in Europe, this study targets to the evaluation of six biopesticides/biostimulants (Botector®, Mycostop®, Serenade Max®, Trianum®, Vacciplant®, and zeolite) for the control of A. flavus and the derived aflatoxins in in vitro and maize field bioassays. Mycostop®, Serenade Max®, Vacciplant®, and zeolite reduced significantly A. flavus conidia production by 38.8-63.1%, and most of them were able to reduce aflatoxin B1 (AFB1) production in laboratory studies. Mycostop®, Trianum®, and Botector® were effective in reducing AFB1, in vitro. In the field, Mycostop® and Botector® treatments resulted in significant reduction of the disease severity (16.5 and 21.9%, respectively) and decreased significantly AFB1 content in maize kernels by 43.05 and 43.09%, respectively. For the first time, these results demonstrated the potential of commercial non-chemical products to suppress disease symptoms and aflatoxin content caused by A. flavus in maize under laboratory and field conditions.

FTIR spectroscopic evaluation of changes in the cellular biochemical composition of the phytopathogenic fungus Alternaria alternata induced by extracts of some Greek medicinal and aromatic plants.

In this study, the biological activity of aquatic extracts of selected Greek medicinal and aromatic plants to the phytopathogenic fungus Alternaria alternata was investigated. Lamiaceae species (Hyssopus officinalis L., Melissa officinalis L., Origanum dictamnus L., Origanum vulgare L. and Salvia officinalis L.) were found to enhance significantly the mycelium growth whereas Crocus sativus appears to inhibit it slightly. M. officinalis and S. officinalis caused the highest stimulation in mycelium growth (+97%) and conidia production (+65%) respectively. In order to further investigate the bioactivity of plant extracts to A. alternata, we employed Fourier Transform Infrared Spectroscopy (FTIR). Differences of original spectra were assigned mainly to amides of proteins. The second derivative transformation of spectra revealed changes in spectral regions corresponding to absorptions of the major cellular constituents such as cell membrane and proteins. Principal component analysis of the second derivative transformed spectra confirmed that fatty acids of the cell membranes, amides of proteins and polysaccharides of the cell wall had the major contribution to data variation. FTIR band area ratios were found to correlate with fungal mycelium growth.

The G protein ß subunit controls virulence and multiple growth- and development-related traits in Verticillium dahliae.

To gain insight into the role of G protein-mediated signaling in virulence and development of the soilborne, wilt causing fungus Verticillium dahliae, the G protein ß subunit gene (named as VGB) was disrupted in tomato race 1 strain of V. dahliae. A resulting mutant strain, 70ΔGb15, displayed drastic reduction in virulence, increased microsclerotia formation and conidiation, and decreased ethylene production compared to the corresponding wild type (wt) strain 70wt-r1. Moreover, 70ΔGb15 exhibited an elongated rather than radial growth pattern on agar media. A transformant of 70ΔGb15 (named as 70ΔGbPKAC1) that carries an extra copy of VdPKAC1, a V. dahliae gene encoding the catalytic subunit of the cAMP-dependent protein kinase A, exhibited wt growth pattern and conidiation, was unable to form microsclerotia, produced high amounts of ethylene, and exhibited virulence between that of 70ΔGb15 and 70wt-r1 on tomato plants. Phenotypical changes observed in 70ΔGb15 and 70ΔGbPKAC1 correlated with transcriptional changes in several genes involved in signaling (MAP kinase VMK1) and development (hydrophobin VDH1 and ACC synthase ACS1) of V. dahliae. Results from the present work suggest a linkage between VGB and VdPKAC1 signaling pathways in regulating virulence, hormone production and development in V. dahliae.

Autophagic components contribute to hypersensitive cell death in Arabidopsis.

Autophagy has been implicated as a prosurvival mechanism to restrict programmed cell death (PCD) associated with the pathogen-triggered hypersensitive response (HR) during plant innate immunity. This model is based on the observation that HR lesions spread in plants with reduced autophagy gene expression. Here, we examined receptor-mediated HR PCD responses in autophagy-deficient Arabidopsis knockout mutants (atg), and show that infection-induced lesions are contained in atg mutants. We also provide evidence that HR cell death initiated via Toll/Interleukin-1 (TIR)-type immune receptors through the defense regulator EDS1 is suppressed in atg mutants. Furthermore, we demonstrate that PCD triggered by coiled-coil (CC)-type immune receptors via NDR1 is either autophagy-independent or engages autophagic components with cathepsins and other unidentified cell death mediators. Thus, autophagic cell death contributes to HR PCD and can function in parallel with other prodeath pathways.

Real-time and semiquantitative RT-PCR methods to analyze gene expression patterns during Aspergillus-host interactions.

Aspergillus species are infamous for causing several plant and animal diseases that directly (e.g., invasive aspergillosis) or indirectly (e.g., consumption of toxic food supplies) can lead to high rates of morbidity in humans and animals worldwide. Despite progress in molecular information and manipulation of Aspergillus spp., including genome sequence availability and suitable transformation methodologies, efforts to control Aspergillus diseases are still far from satisfactory, due in part to lack of knowledge of fungal virulence attributes. In order to obtain meaningful insights on the disease mechanism(s), it is essential to detect virulence gene expression during host invasion. Here, we describe two PCR-based detection methods of Aspergillus gene expression in both plant and mammalian tissues. Moreover, these techniques can be employed for routine screening of large numbers of aspergilli to improve diagnosis, disease monitoring, and therapy of fungal disease.

The F-box protein ACRE189/ACIF1 regulates cell death and defense responses activated during pathogen recognition in tobacco and tomato.

Virus-induced gene silencing identified the Avr9/Cf-9 RAPIDLY ELICITED gene ACRE189 as essential for the Cf-9- and Cf-4-mediated hypersensitive response (HR) in Nicotiana benthamiana. We report a role for ACRE189 in disease resistance in tomato (Solanum lycopersicum) and tobacco (Nicotiana tabacum). ACRE189 (herein renamed Avr9/Cf-9-INDUCED F-BOX1 [ACIF1]) encodes an F-box protein with a Leu-rich-repeat domain. ACIF1 is widely conserved and is closely related to F-box proteins regulating plant hormone signaling. Silencing of tobacco ACIF1 suppressed the HR triggered by various elicitors (Avr9, Avr4, AvrPto, Inf1, and the P50 helicase of Tobacco mosaic virus [TMV]). ACIF1 is recruited to SCF complexes (a class of ubiquitin E3 ligases), and the expression of ACIF1 F-box mutants in tobacco compromises the HR similarly to ACIF1 silencing. ACIF1 affects N gene-mediated responses to TMV infection, including lesion formation and salicylic acid accumulation. Loss of ACIF1 function also reduced confluent cell death induced by Pseudomonas syringae pv tabaci. ACIF1 silencing in Cf9 tomato attenuated the Cf-9-dependent HR but not Cf-9 resistance to Cladosporium fulvum. Resistance conferred by the Cf-9 homolog Cf-9B, however, was compromised in ACIF1-silenced tomato. Analysis of public expression profiling data suggests that Arabidopsis thaliana homologs of ACIF1 (VFBs) regulate defense responses via methyl jasmonate- and abscisic acid-responsive genes. Together, these findings support a role of ACIF1/VFBs in plant defense responses.

Reciprocal oxylipin-mediated cross-talk in the Aspergillus-seed pathosystem.

In Aspergilli, mycotoxin production and sporulation are governed, in part, by endogenous oxylipins (oxygenated, polyunsaturated fatty acids and metabolites derived therefrom). In Aspergillus nidulans, oxylipins are synthesized by the dioxygenase enzymes PpoA, PpoB and PpoC. Structurally similar oxylipins are synthesized in seeds via the action of lipoxygenase (LOX) enzymes. Previous reports have shown that exogenous application of seed oxylipins to Aspergillus cultures alters sporulation and mycotoxin production. Herein, we explored whether a plant oxylipin biosynthetic gene (ZmLOX3) could substitute functionally for A. nidulans ppo genes. We engineered ZmLOX3 into wild-type A. nidulans, and into a DeltappoAC strain that was reduced in production of oxylipins, conidia and the mycotoxin sterigmatocystin. ZmLOX3 expression increased production of conidia and sterigmatocystin in both backgrounds. We additionally explored whether A. nidulans oxylipins affect seed LOX gene expression during Aspergillus colonization. We observed that peanut seed pnlox2-3 expression was decreased when infected by A. nidulansDeltappo mutants compared with infection by wild type. This result provides genetic evidence that fungal oxylipins are involved in plant LOX gene expression changes, leading to possible alterations in the fungal/host interaction. This report provides the first genetic evidence for reciprocal oxylipin cross-talk in the Aspergillus-seed pathosystem.

Oxylipins as developmental and host-fungal communication signals.

Pathogenic microbes and their hosts have acquired complex signalling mechanisms to appraise themselves of the environmental milieu in the ongoing battle for survival. Several recent studies have implicated oxylipins as a novel class of host-microbe signalling molecules. Oxylipins represent a vast and diverse family of secondary metabolites that originate from the oxidation or further conversion of polyunsaturated fatty acids. Among the microbial oxylipins, the fungal oxylipins are best characterized and function as hormone-like signals that modulate the timing and balance between asexual and sexual spore development in addition to toxin production. Coupled with other studies that implicate a role for fungal oxylipins in pathogenesis by Aspergillus and Candida spp., these results suggest that host and microbial oxylipins might interfere with the metabolism, perception or signalling processes of each other.

Inducible cell death in plant immunity.

Programmed cell death (PCD) occurs during vegetative and reproductive plant growth, as typified by autumnal leaf senescence and the terminal differentiation of the endosperm of cereals which provide our major source of food. PCD also occurs in response to environmental stress and pathogen attack, and these inducible PCD forms are intensively studied due their experimental tractability. In general, evidence exists for plant cell death pathways which have similarities to the apoptotic, autophagic and necrotic forms described in yeast and metazoans. Recent research aiming to understand these pathways and their molecular components in plants are reviewed here.