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666 I. Introduction 667 II. Biosynthesis 667 III. Meta-analysis 669 IV. The type of stress influences the total amount of GLVs released 669 V. Herbivores can modulate the wound-induced release of GLVs 669 VI. Fungal infection greatly induces GLV production 672 VII. Monocots and eudicots respond differentially to different types of stress 673 VIII. The type of stress does not influence the proportion of GLVs per chemical class 673 IX. The type of stress does influence the isomeric ratio within each chemical class 674 X. GLVs: from signal perception to signal transduction 676 XI. GLVs influence the C/N metabolism 677 XII. Interaction with plant hormones 678 XIII. General conclusions and unanswered questions 678 Acknowledgements 679 References 679 SUMMARY: Plants respond to stress by releasing biogenic volatile organic compounds (BVOCs). Green leaf volatiles (GLVs), which are abundantly produced across the plant kingdom, comprise an important group within the BVOCs. They can repel or attract herbivores and their natural enemies; and they can induce plant defences or prime plants for enhanced defence against herbivores and pathogens and can have direct toxic effects on bacteria and fungi. Unlike other volatiles, GLVs are released almost instantly upon mechanical damage and (a)biotic stress and could thus function as an immediate and informative signal for many organisms in the plant's environment. We used a meta-analysis approach in which data from the literature on GLV production during biotic stress responses were compiled and interpreted. We identified that different types of attackers and feeding styles add a degree of complexity to the amount of emitted GLVs, compared with wounding alone. This meta-analysis illustrates that there is less variation in the GLV profile than we presumed, that pathogens induce more GLVs than insects and wounding, and that there are clear differences in GLV emission between monocots and dicots. Besides the meta-analysis, this review provides an update on recent insights into the perception and signalling of GLVs in plants., (© 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.)

Numerous herbivore-induced plant volatiles (HIPVs) play important roles in plant defense. In tea plants (Camellia sinensis), (Z)-3-hexenyl acetate (3-HAC) has been characterized as associated with resistance to herbivores. To date, how tea plants biosynthesize and regulate 3-HAC to resist herbivores remain unclear. Based on transcriptomes assembled from Ectropis obliqua-fed leaves, a cDNA encoding BAHD acyltransferase, namely CsCHAT1, was highly induced in leaves fed with E. obliqua. Enzymatic assays showed that CsCHAT1 converted (Z)-3-hexenol into 3-HAC. Further suppression of CsCHAT1 expression reduced the accumulation of 3-HAC and lowered the resistance of tea plants to E. obliqua, while 3-HAC replenishment rescued the reduced resistance of CsCHAT1-silenced tea plants against E. obliqua. Two transcription factors (TFs), CsNAC30 and CsTCP11, were co-expressed with CsCHAT1. An integrative approach of biochemistry, DNA-protein interaction, gene silencing, and metabolic profiling revealed that the two TFs positively regulated the expression of CsCHAT1. The suppression of either one decreased the production of 3-HAC and eliminated the resistance of tea plants to E. obliqua. Notably, the suppression of either one considerably impaired JA-induced 3-HAC biosynthesis in tea plant. The proposed pathway can be targeted for innovative agro-biotechnologies protecting tea plants from damage by E. obliqua., (© 2024 The Author(s). New Phytologist © 2024 New Phytologist Foundation.)

The effects of drought stress on stomatal opening dynamics, plant volatile organic compound (VOC) emissions and plant-insect interactions have been well-documented individually, but how they interact mechanistically remains poorly studied. Here, we studied how drought-triggered stomatal closure affects VOC emission and plant-trophic interactions by combining RNAi silencing, molecular biological and chemical analyses (GC-MS) of a potato-tuber moth-egg parasitoid tritrophic system. Drought stress attenuated stomatal apertures and VOC emissions, which made the potato (Solanum tuberosum L.) plants more attractive to the herbivore but less attractive to the parasitoid. Stomatal aperture manipulations through StSLAC1 gene knockdown and chemical treatments (ABA and 5-aminolevulinic acid) consistently affected drought-triggered VOC emissions and plant-herbivore-parasitoid interactions, supporting aperture-dependent VOC emission. RNA-Seq analysis revealed that drought stress did not transcriptionally inhibit VOC biosynthesis. Collectively, our findings are consistent with the stomatal regulation of plant-insect interactions through the modulation of VOC emissions under drought stress. This highlights the intricate interplay between stomatal dynamics, VOC emission and plant-insect interactions., (© 2025 The Author(s). New Phytologist © 2025 New Phytologist Foundation.)

Summary: Strigolactones (SLs) are carotenoid‐derived phytohormones that regulate plant growth and development. While root‐secreted SLs are well‐known to facilitate plant symbiosis with beneficial microbes, the role of SLs in plant interactions with pathogenic microbes remains largely unexplored.Using genetic and biochemical approaches, we demonstrate a negative role of SLs in rice (Oryza sativa) defense against the blast fungus Pyricularia oryzae (syn. Magnaporthe oryzae).We found that SL biosynthesis and perception mutants, and wild‐type (WT) plants after chemical inhibition of SLs, were less susceptible to P. oryzae. Strigolactone deficiency also resulted in a higher accumulation of jasmonates, soluble sugars and flavonoid phytoalexins in rice leaves. Likewise, in response to P. oryzae infection, SL signaling was downregulated, while jasmonate and sugar content increased markedly. The jar1 mutant unable to synthesize jasmonoyl‐l‐isoleucine, and the coi1‐18 RNAi line perturbed in jasmonate signaling, both accumulated lower levels of sugars. However, when WT seedlings were sprayed with glucose or sucrose, jasmonate accumulation increased, suggesting a reciprocal positive interplay between jasmonates and sugars. Finally, we showed that functional jasmonate signaling is necessary for SL deficiency to induce rice defense against P. oryzae.We conclude that a reduction in rice SL content reduces P. oryzae susceptibility by activating jasmonate and sugar signaling pathways, and flavonoid phytoalexin accumulation. [ABSTRACT FROM AUTHOR]

Plants typically activate distinct defense pathways against various pathogens. Heightened resistance to one pathogen often coincides with increased susceptibility to another pathogen. However, the underlying molecular basis of this antagonistic response remains unclear. Here, we demonstrate that mutants defective in the transcription factor ETHYLENE-INSENSITIVE 3-LIKE 2 (OsEIL2) exhibited enhanced resistance to the biotrophic bacterial pathogen Xanthomonas oryzae pv oryzae and to the hemibiotrophic fungal pathogen Magnaporthe oryzae, but enhanced susceptibility to the necrotrophic fungal pathogen Rhizoctonia solani. Furthermore, necrotroph-induced OsEIL2 binds to the promoter of OsWRKY67 with high affinity, leading to the upregulation of salicylic acid (SA)/jasmonic acid (JA) pathway genes and increased SA/JA levels, ultimately resulting in enhanced resistance. However, biotroph- and hemibiotroph-induced OsEIL2 targets OsERF083, resulting in the inhibition of SA/JA pathway genes and decreased SA/JA levels, ultimately leading to reduced resistance. Our findings unveil a previously uncharacterized defense mechanism wherein two distinct transcriptional regulatory modules differentially mediate immunity against pathogens with different lifestyles through the transcriptional reprogramming of phytohormone pathway genes., (© 2024 The Authors. New Phytologist © 2024 New Phytologist Foundation.)

Biosynthesis of flavonoid aglycones and glycosides is well established. However, key genes involved in their catabolism are poorly understood, even though the products of hydrolysis and oxidation play important roles in plant resistance to biotic stress. Here, we report on catabolism of dihydrochalcones (DHCs), the most abundant flavonoids in domesticated apple and wild Malus. Two key genes, BGLU13.1 and PPO05, were identified by activity-directed protein purification. BGLU13.1-A hydrolyzed phlorizin, (the most abundant DHC in domesticated apple) to produce phloretin which was then oxidized by PPO05. The process differed in some wild Malus, where trilobatin (a positional isomer of phlorizin) was mainly oxidized by PPO05. The effects of DHC catabolism on apple resistance to biotic stresses was investigated using transgenic plants. Either directly or indirectly, phlorizin hydrolysis affected resistance to the phytophagous pest two-spotted spider mite, while oxidation of trilobatin was involved in resistance to the biotrophic fungus Podosphaera leucotricha. DHC catabolism did not affect apple resistance to necrotrophic pathogens Valsa mali and Erwinia amylovara. These results suggest that different DHC catabolism pathways play different roles in apple resistance to biotic stresses. The role of DHC catabolism on apple resistance appeared closely related to the mode of invasion/damage used by pathogen/pest., (© 2024 The Authors. New Phytologist © 2024 New Phytologist Foundation.)

Summary: The steady‐state level of histone acetylation is maintained by histone acetyltransferase (HAT) and histone deacetylase (HDAC) complexes. INhibitor of Growth (ING) proteins are key components of the HAT or HDAC complexes but their relationship with other components and roles in phytopathogenic fungi are not well‐characterized.Here, the FNG3 ING gene was functionally characterized in the wheat head blight fungus Fusarium graminearum. Deletion of FNG3 results in defects in fungal development and pathogenesis. Unlike other ING proteins that are specifically associated with distinct complexes, Fng3 was associated with both NuA3 HAT and FgRpd3 HDAC complexes to regulate H3 acetylation and H4 deacetylation.Whereas FgNto1 mediates the FgSas3–Fng3 interaction in the NuA3 complex, Fng3 interacted with the C‐terminal region of FgRpd3 that is present in Rpd3 orthologs from filamentous fungi but absent in yeast Rpd3. The intrinsically disordered regions in the C‐terminal tail of FgRpd3 underwent phase separation, which was important for its interaction with Fng3. Furthermore, the ING domain of Fng3 is responsible for its specificities in protein–protein interactions and functions.Taken together, Fng3 is involved in the dynamic regulation of histone acetylation by interacting with two histone modification complexes, and is important for fungal development and pathogenicity. [ABSTRACT FROM AUTHOR]

Summary: Rice diterpenoid phytoalexins (DPs) are secondary metabolites with a well known role in resistance to foliar pathogens. As DPs are also known to be produced and exuded by rice roots, we hypothesised that they might play an important role in plant–nematode interactions, and particularly in defence against phytoparasitic nematodes.We used transcriptome analysis on rice roots to analyse the effect of infection by the root‐knot nematode Meloidogyne graminicola or treatment with resistance‐inducing chemical stimuli on DP biosynthesis genes, and assessed the susceptibility of mutant rice lines impaired in DP biosynthesis to M. graminicola. Moreover, we grew these mutants and their wild‐type in field soil and used metabarcoding to assess the effect of impairment in DP biosynthesis on rhizosphere and root nematode communities.We show that M. graminicola suppresses DP biosynthesis genes early in its invasion process and, conversely, that resistance‐inducing stimuli transiently induce the biosynthesis of DPs. Moreover, we show that loss of DPs increases susceptibility to M. graminicola. Metabarcoding on wild‐type and DP‐deficient plants grown in field soil reveals that DPs significantly alter the composition of rhizosphere and root nematode communities.Diterpenoid phytoalexins are important players in basal and inducible defence against nematode pathogens of rice and help shape rice‐associated nematode communities. [ABSTRACT FROM AUTHOR]

Summary: Some canonical plant hormones such as auxins and gibberellins have precursors that are biogenic volatiles (indole, indole acetonitrile, phenylacetaldoxime and ent‐kaurene). Cytokinins, abscisic acid and strigolactones are hormones comprising chemical moieties that have distinct volatile analogues, and are synthesised alongside constitutively emitted volatiles (isoprene, sesquiterpenes, lactones, benzenoids and apocarotenoid volatiles). Nonvolatile hormone analogues and biogenic volatile organic compounds (BVOCs) evolved in tandem as growth and behavioural regulators in unicellular organisms. In plants, however, nonvolatile hormones evolved as regulators of growth, development and differentiation, while endogenous BVOCs (often synthesised lifelong) became subtle regulators of hormone synthesis, availability, activity and turnover, all supported by functionally redundant components of hormone metabolism. Reciprocal changes in the abundance and activity of hormones, nitric oxide, and constitutive plant volatiles constantly bridge retrograde and anterograde signalling to maintain hormone equilibria even in unstressed plants. This is distinct from transient interference in hormone signalling by stress‐induced and exogenously received volatiles. [ABSTRACT FROM AUTHOR]

Summary: The ability to predict future risks is essential for many organisms, including plants. Plants can gather information about potential future herbivory by detecting volatiles that are emitted by herbivore‐attacked neighbors. Several individual volatiles have been identified as active danger cues. Recent work has also shown that plants may integrate multiple volatiles into their defense responses. Here, I discuss how the integration of multiple volatiles can increase the capacity of plants to predict future herbivore attack. I propose that integration of multiple volatile cues does not occur at the perception stage, but may through downstream early defense signaling and then be further consolidated by hormonal crosstalk. Exploring plant volatile cue integration can facilitate our understanding and utilization of chemical information transfer. [ABSTRACT FROM AUTHOR]

Summary: Investigation into plant–fungal pathogen interactions is one of the most interesting fields in plant sciences. However, the roles of plant volatile organic compounds in the arms race are still largely unknown.Based on precise quantification of plant volatiles, we discovered that the plant volatile organic compound (E)‐2‐hexenal, at concentrations that were similar to or lower than those in tissues of strawberry and tomato fruits, upregulates sulfate assimilation in spores and hyphae of the phytopathogenic fungus Botrytis cinerea. This upregulation is independent of the types of sulfur sources in the plant and can be achieved in the presence of inorganic sulfate and organic sulfur sources.Using the fungal deletion mutants, we further found that sulfate assimilation is involved in the infection of tomato and strawberry fruits by B. cinerea, and that the severity of the disease is proportional to the sulfate content in the fruits. Both before and during the infection, (E)‐2‐hexenal induced utilisation of plant sulfate by B. cinerea facilitates its pathogenesis through enhancing its tolerance to oxidative stress.This work provides novel insights into the role of plant volatiles in plant–fungal pathogen interaction and highlights the importance of sulfur levels in the host in the prevention of grey mould disease. [ABSTRACT FROM AUTHOR]

Summary: Herbivore‐induced plant volatiles (HIPVs) are widely recognized as an ecologically important defensive response of plants against herbivory. Although the induction of this 'cry for help' has been well documented, only a few studies have investigated the inhibition of HIPVs by herbivores and little is known about whether herbivores have evolved mechanisms to inhibit the release of HIPVs.To examine the role of herbivore effectors in modulating HIPVs and stomatal dynamics, we conducted series of experiments combining pharmacological, surgical, genetic (CRISPR‐Cas9) and chemical (GC‐MS analysis) approaches.We show that the salivary enzyme, glucose oxidase (GOX), secreted by the caterpillar Helicoverpa zea on leaves, causes stomatal closure in tomato (Solanum lycopersicum) within 5 min, and in both tomato and soybean (Glycine max) for at least 48 h. GOX also inhibits the emission of several HIPVs during feeding by H. zea, including (Z)‐3‐hexenol, (Z)‐jasmone and (Z)‐3‐hexenyl acetate, which are important airborne signals in plant defenses.Our findings highlight a potential adaptive strategy where an insect herbivore inhibits plant airborne defenses during feeding by exploiting the association between stomatal dynamics and HIPV emission. [ABSTRACT FROM AUTHOR]

Summary: Pathogens use effectors to suppress host defence mechanisms, promote the derivation of nutrients, and facilitate infection within the host plant. Much is now known about effectors that target biotic pathways, particularly those that interfere with plant innate immunity. By contrast, an understanding of how effectors manipulate nonimmunity pathways is only beginning to emerge. Here, we focus on exciting new insights into effectors that target abiotic stress adaptation pathways, tampering with key functions within the plant to promote colonization. We critically assess the role of various signalling agents in linking different pathways upon perturbation by pathogen effectors. Additionally, this review provides a summary of currently known bacterial, fungal, and oomycete pathogen effectors that induce biotic and abiotic stress responses in the plant, as a first step towards establishing a comprehensive picture for linking effector targets to pathogenic lifestyles. [ABSTRACT FROM AUTHOR]

Summary: Species‐rich seminatural grasslands in Central Europe have suffered a dramatic loss of biodiversity due to conversion to arable land, but vast areas are being restored. Population recovery of orchids, which depend on mycorrhizal fungi for germination, is however limited. We hypothesised that ploughing and fertilisation caused shifts in orchid mycorrhizal communities in soil and restricted orchid germination.We examined edaphic conditions in 60 restored and seminatural grasslands, and germination success in 10 restored grasslands. Using a newly designed primer, we screened the composition of rhizoctonias in soil, seedlings and roots of seven orchid species.Seminatural and restored grasslands differed significantly in nutrient amounts and rhizoctonia assemblages in soil. While Serendipitaceae prevailed in seminatural grasslands with a higher organic matter content, Ceratobasidiaceae were more frequent in phosphorus‐rich restored grasslands with increased abundance on younger restored sites. Tulasnellaceae displayed no preference. Germination success in restored grasslands differed significantly between orchid species; two mycorrhizal generalist species germinated with a broad range of rhizoctonias at most restored grasslands, while germination success of specialists was low.Past agricultural practices have a long‐lasting effect on soil conditions and orchid mycorrhizal communities. Altered mycorrhizal availability may be the main reason for low germination success of specialist orchid species. [ABSTRACT FROM AUTHOR]

Summary: At the colonization site of a foreign entity, plant cells alter their trajectory of growth and development. The resulting structure – a plant gall – accommodates various needs of the foreigner, which are phylogenetically diverse: viruses, bacteria, protozoa, oomycetes, true fungi, parasitic plants, and many types of animals, including rotifers, nematodes, insects, and mites. The plant species that make galls also are diverse. We assume gall production costs the plant. All is well if the foreigner provides a gift that makes up for the cost. Nitrogen‐fixing nodule‐inducing bacteria provide nutritional services. Gall wasps pollinate fig trees. Unfortunately for plants, most galls are made for foes, some of which are deeply studied pathogens and pests: Agrobacterium tumefaciens, Rhodococcus fascians, Xanthomonas citri, Pseudomonas savastanoi, Pantoea agglomerans, 'Candidatus' phytoplasma, rust fungi, Ustilago smuts, root knot and cyst nematodes, and gall midges. Galls are an understudied phenomenon in plant developmental biology. We propose gall inception for discovering unifying features of the galls that plants make for friends and foes, talk about molecules that plants and gall‐inducers use to get what they want from each other, raise the question of whether plants colonized by arbuscular mycorrhizal fungi respond in a gall‐like manner, and present a research agenda. [ABSTRACT FROM AUTHOR]

Summary: Strigolactones (SLs) are carotenoid‐derived plant hormones that also act in the rhizosphere to stimulate germination of root‐parasitic plants and enhance plant symbiosis with beneficial microbes. Here, the role of SLs was investigated in the interaction of rice (Oryza sativa) roots with the root‐knot nematode Meloidogyne graminicola.Genetic approaches and chemical sprays were used to manipulate SL signaling in rice before infection with M. graminicola. Then, nematode performance was evaluated and plant defense hormones were quantified.Meloidogyne graminicola infection induced SL biosynthesis and signaling and suppressed jasmonic acid (JA)‐based defense in rice roots, suggesting a potential role of SLs during nematode infection. Whereas the application of a low dose of the SL analogue GR24 increased nematode infection and decreased jasmonate accumulation, the SL biosynthesis and signaling d mutants were less susceptible to M. graminicola, and constitutively accumulated JA and JA‐isoleucine compared with wild‐type plants. Spraying with 0.1 μM GR24 restored nematode susceptibility in SL‐biosynthesis mutants but not in the signaling mutant. Furthermore, foliar application of the SL biosynthesis inhibitor TIS108 impeded nematode infection and increased jasmonate levels in rice roots.In conclusion, SL signaling in rice suppresses jasmonate accumulation and promotes root‐knot nematode infection. [ABSTRACT FROM AUTHOR]

Summary: The wheat Lr34res allele, coding for an ATP‐binding cassette transporter, confers durable resistance against multiple fungal pathogens. The Lr34sus allele, differing from Lr34res by two critical nucleotide polymorphisms, is found in susceptible wheat cultivars. Lr34res is functionally transferrable as a transgene into all major cereals, including rice, barley, maize, and sorghum.Here, we used transcriptomics, physiology, genetics, and in vitro and in vivo transport assays to study the molecular function of Lr34.We report that Lr34res results in a constitutive induction of transcripts reminiscent of an abscisic acid (ABA)‐regulated response in transgenic rice. Lr34‐expressing rice was altered in biological processes that are controlled by this phytohormone, including dehydration tolerance, transpiration and seedling growth. In planta seedling and in vitro yeast accumulation assays revealed that both LR34res and LR34sus act as ABA transporters. However, whereas the LR34res protein was detected in planta the LR34sus version was not, suggesting a post‐transcriptional regulatory mechanism.Our results identify ABA as a substrate of the LR34 ABC transporter. We conclude that LR34res‐mediated ABA redistribution has a major effect on the transcriptional response and physiology of Lr34res‐expressing plants and that ABA is a candidate molecule that contributes to Lr34res‐mediated disease resistance. [ABSTRACT FROM AUTHOR]

Summary: Molecular plant–fungal interaction studies have mainly focused on small secreted protein effectors. However, accumulating evidence shows that numerous fungal secondary metabolites are produced at all stages of plant colonization, especially during early asymptomatic/biotrophic phases. The discovery of fungal small RNAs targeting plant transcripts has expanded the fungal repertoire of nonproteinaceous effectors even further. The challenge now is to develop specific functional methods to fully understand the biological roles of these effectors. Studies on fungal extracellular vesicles are also needed because they could be the universal carriers of all kinds of fungal effectors. With this review, we aim to stimulate the nonproteinaceous effector research field to move from descriptive to functional studies, which should bring a paradigm shift in plant–fungal interactions. [ABSTRACT FROM AUTHOR]

Summary: Blumeria graminis f. sp. tritici (B.g. tritici) is the causal agent of the wheat powdery mildew disease. The highly fragmented B.g. tritici genome available so far has prevented a systematic analysis of effector genes that are known to be involved in host adaptation. To study the diversity and evolution of effector genes we produced a chromosome‐scale assembly of the B.g. tritici genome.The genome assembly and annotation was achieved by combining long‐read sequencing with high‐density genetic mapping, bacterial artificial chromosome fingerprinting and transcriptomics.We found that the 166.6 Mb B.g. tritici genome encodes 844 candidate effector genes, over 40% more than previously reported. Candidate effector genes have characteristic local genomic organization such as gene clustering and enrichment for recombination‐active regions and certain transposable element families. A large group of 412 candidate effector genes shows high plasticity in terms of copy number variation in a global set of 36 isolates and of transcription levels.Our data suggest that copy number variation and transcriptional flexibility are the main drivers for adaptation in B.g. tritici. The high repeat content may play a role in providing a genomic environment that allows rapid evolution of effector genes with selection as the driving force. [ABSTRACT FROM AUTHOR]

Deficiency of abscisic acid (ABA) in the sitiens mutant of tomato (Solanum lycopersicum) culminates in increased resistance to Botrytis cinerea through a rapid epidermal hypersensitive response (HR) and associated phenylpropanoid pathway-derived cell wall fortifications. This study focused on understanding the role of primary carbon : nitrogen (C : N) metabolism in the resistance response of sitiens to B. cinerea. How alterations in C : N metabolism are linked with the HR-mediated epidermal arrest of the pathogen has been also investigated. Temporal alterations in the γ-aminobutyric acid (GABA) shunt, glutamine synthetase/glutamate synthase (GS/GOGAT) cycle and phenylpropanoid pathway were transcriptionally, enzymatically and metabolically monitored in both wild-type and sitiens plants. Virus-induced gene silencing, microscopic analyses and pharmacological assays were used to further confirm the data. Our results on the sitiens-B. cinerea interaction favor a model in which cell viability in the cells surrounding the invaded tissue is maintained by a constant replenishment of the tricarboxylic acid (TCA) cycle through overactivation of the GS/GOGAT cycle and the GABA shunt, resulting in resistance through both tightly controlling the defense-associated HR and slowing down the pathogen-induced senescence. Collectively, this study shows that maintaining cell viability via alterations in host C : N metabolism plays a vital role in the resistance response against necrotrophic pathogens., (© 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.)

Studies involving plant-nematode interactions provide an opportunity to unravel plant defense signaling in root tissues. In this study, we have characterized the roles of salicylate (SA), jasmonate (JA), ethylene (ET) and abscisic acid (ABA) in plant defense against the migratory nematode Hirschmanniella oryzae in the monocot model plant rice (Oryza sativa). Experiments with exogenous hormone applications, biosynthesis inhibition and mutant/transgenic lines were executed to test the effect on H. oryzae parasitism in rice roots. Our results demonstrate that an intact ET, JA and SA biosynthesis pathway is a prerequisite for defense against H. oryzae. By contrast, exogenous ABA treatment drastically compromised the rice defense towards this nematode. Gene expression analyses using quantitative reverse transcription polymerase chain reaction (qRT-PCR) demonstrate that the disease-inducing effect of ABA is likely to be the result of an antagonistic interaction between this hormone and the SA/JA/ET-dependent basal defense system. Collectively, in rice defense against H. oryzae, at least three pathways, namely SA, JA and ET, are important, while ABA plays a negative role in defense. Our results suggest that the balance of ABA and SA/JA/ET signaling is an important determinant for the outcome of the rice-H. oryzae interaction., (© 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.)

• Priming of defence is a strategy employed by plants exposed to stress to enhance resistance against future stress episodes with minimal associated costs on growth. Here, we test the hypothesis that application of priming agents to seeds can result in plants with primed defences. • We measured resistance to arthropod herbivores and disease in tomato (Solanum lycopersicum) plants grown from seed treated with jasmonic acid (JA) and/or β-aminobutryric acid (BABA). • Plants grown from JA-treated seed showed increased resistance against herbivory by spider mites, caterpillars and aphids, and against the necrotrophic fungal pathogen, Botrytis cinerea. BABA seed treatment provided primed defence against powdery mildew disease caused by the biotrophic fungal pathogen, Oidium neolycopersici. Priming responses were long-lasting, with significant increases in resistance sustained in plants grown from treated seed for at least 8 wk, and were associated with enhanced defence gene expression during pathogen attack. There was no significant antagonism between different forms of defence in plants grown from seeds treated with a combination of JA and BABA. • Long-term defence priming by seed treatments was not accompanied by reductions in growth, and may therefore be suitable for commercial exploitation., (© 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.)

Here, the link between UV-B stimulus and the abscisic acid (ABA)-induced nitricoxide (NO) synthesis pathway was studied in leaves of maize (Zea mays).The ABA concentration increased by 100% in UV-B irradiated leaves. Leaves of viviparous 14 (vp14), a mutant defective in ABA synthesis, were more sensitive to UV-B-induced damage than those of the wild type (wt). ABA supplementation attenuated UV-B-induced damage in both the wt and vp14. The hydrogen peroxide(H2O2) concentration increased in the irradiated wt, but changed only slightly in vp14. This increase was prevented by diphenylene iodonium (DPI), an inhibitor of NADPH oxidase (pNOX).NO was detected using the fluorophore 4,5-diamino-fluorescein diacetate(DAF-2DA). DAF-2DA fluorescence increased twofold in UV-B-irradiated wt leaves but not in vp14 leaves. H2O2 and NO production was restored in vp14 plants supplied with 100 μM ABA. Catalase, DPI and the NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) partially blocked UV-B-induced NO accumulation, suggesting that H2O2 as well as NOS-like activity is required for a full plant response to UV-B. NO protects against UV-B-induced cell damage.Our results suggest that UV-B perception triggers an increase in ABA concentration,which activates pNOX and H2O2 generation, and that an NOS-like-dependent mechanism increases NO production to maintain cell homeostasis and attenuate UV-B-derived cell damage.

This article is an Editorial on the special feature issue 'New insights into plant volatiles', which is published in this issue and which includes the following articles: Ameye et al., pp. 666–683; Sharifi et al. pp. 684–691; Moreira et al., pp. 703–713; Pichersky & Raguso, pp. 692–702; Chen et al., pp. 714–725; Danner et al., pp. 726–738; Junker et al., pp. 739–749; Rering et al., pp. 750–759; Eberl et al., pp. 760–772; Fernández‐Martínez et al., pp. 773–784; Glenny et al., pp. 785–798 and Visakorpi et al., pp. 799–810. [ABSTRACT FROM AUTHOR]

Various rhizosphere bacteria are potential (micro)biological pesticides which are able to protect plants against diseases and improve plant yield. Knowledge of the molecular mechanisms that govern these beneficial plant-microbe interactions enables optimization, enhancement and identification of potential synergistic effects in plant protection. The production of antifungal metabolites, induction of systemic resistance, and the ability to compete efficiently with other resident rhizobacteria are considered to be important prerequisites for the optimal performance of biocontrol agents. Intriguing aspects in the molecular mechanisms of these processes have been discovered recently. Phenazines and phloroglucinols are major determinants of biological control of soilborne plant pathogens by various strains of fluorescent Pseudomonas spp. This review focuses on the current state of knowledge on biocontrol by phenazine-producing Pseudomonas strains and the action, biosynthesis, and regulation mechanisms of the production of microbial phenazines.

The ability to predict future risks is essential for many organisms, including plants. Plants can gather information about potential future herbivory by detecting volatiles that are emitted by herbivore-attacked neighbors. Several individual volatiles have been identified as active danger cues. Recent work has also shown that plants may integrate multiple volatiles into their defense responses. Here, I discuss how the integration of multiple volatiles can increase the capacity of plants to predict future herbivore attack. I propose that integration of multiple volatile cues does not occur at the perception stage, but may through downstream early defense signaling and then be further consolidated by hormonal crosstalk. Exploring plant volatile cue integration can facilitate our understanding and utilization of chemical information transfer., (© 2021 The Author. New Phytologist © 2021 New Phytologist Foundation.)

Accumulating data indicate that strigolactones ( SLs) are implicated in the response to environmental stress, implying a potential effect of SLs on stomatal response and thus stress acclimatization. In this study, we investigated the molecular mechanism underlying the effect of SLs on stomatal response and their interrelation with abscisic acid ( ABA) signaling., The impact of SLs on the stomatal response was investigated by conducting SL-feeding experiments and by analyzing SL-related mutants. The involvement of endogenous ABA and ABA-signaling components in SL-mediated stomatal closure was physiologically evaluated using genetic mutants. Pharmacological and genetic approaches were employed to examine hydrogen peroxide (H2O2) and nitric oxide ( NO) production., SL-related mutants exhibited larger stomatal apertures, while exogenous SLs were able to induce stomatal closure and rescue the more widely opening stomata of SL-deficient mutants. The SL-biosynthetic genes were induced by abiotic stress in shoot tissues. Disruption of ABA-biosynthetic genes, as well as genes that function in guard cell ABA signaling, resulted in no impairment in SL-mediated stomatal response. However, disruption of MORE AXILLARY GROWTH2 ( MAX2), DWARF14 ( D14), and the anion channel gene SLOW ANION CHANNEL-ASSOCIATED 1 (SLAC1) impaired SL-triggered stomatal closure. SLs stimulated a marked increase in H2O2 and NO contents, which is required for stomatal closure., Our results suggest that SLs play a prominent role, together with H2O2/ NO production and SLAC1 activation, in inducing stomatal closure in an ABA-independent mechanism. [ABSTRACT FROM AUTHOR]

• There is a large diversity of genetically defined resistance genes in bread wheat against the powdery mildew pathogen Blumeria graminis (B. g.) f. sp. tritici. Many confer race-specific resistance to this pathogen, but until now only the mildew avirulence gene AvrPm3a2/f2 that is recognized by Pm3a/f was known molecularly. • We performed map-based cloning and genome-wide association studies to isolate a candidate for the mildew avirulence gene AvrPm2. We then used transient expression assays in Nicotiana benthamiana to demonstrate specific and strong recognition of AvrPm2 by Pm2. • The virulent AvrPm2 allele arose from a conserved 12 kb deletion, while there is no protein sequence diversity in the gene pool of avirulent B. g. tritici isolates. We found one polymorphic AvrPm2 allele in B. g. triticale and one orthologue in B. g. secalis and both are recognized by Pm2. AvrPm2 belongs to a small gene family encoding structurally conserved RNase-like effectors, including Avra13 from B. g. hordei, the cognate Avr of the barley resistance gene Mla13. • These results demonstrate the conservation of functional avirulence genes in two cereal powdery mildews specialized on different hosts, thus providing a possible explanation for successful introgression of resistance genes from rye or other grass relatives to wheat. [ABSTRACT FROM AUTHOR]

Root colonization by the beneficial fungus Piriformospora indica is controlled by plant innate immunity, but factors that channel this interaction into a mutualistic relationship are not known. We have explored the impact of abscisic acid ( ABA) and osmotic stress on the P. indica interaction with Arabidopsis thaliana., The activation of plant innate immunity in roots was determined by measuring the concentration of the phytoalexin camalexin and expression of transcription factors regulating the biosynthesis of tryptophan-related defence metabolites. Furthermore, the impact of the fungus on the content of ABA, salicylic acid, jasmonic acid ( JA) and JA-related metabolites was examined., We demonstrated that treatment with exogenous ABA or the ABA analogue pyrabactin increased fungal colonization efficiency without impairment of plant fitness. Concomitantly, ABA-deficient mutants of A. thaliana ( aba1-6 and aba2-1) were less colonized, while plants exposed to moderate stress were more colonized than corresponding controls. Sustained exposure to ABA attenuated expression of transcription factors MYB51, MYB122 and WRKY33 in roots upon P. indica challenge or chitin treatment, and prevented an increase in camalexin content., The results indicate that ABA can strengthen the interaction with P. indica as a consequence of its impact on plant innate immunity. Consequently, ABA will be relevant for the establishment and outcome of the symbiosis under stress conditions. [ABSTRACT FROM AUTHOR]

• Agrobacterium tumefaciens causes crown gall disease. Although Agrobacterium can be popularly used for genetic engineering, the influence of aboveground insect infestation on Agrobacterium induced gall formation has not been investigated. • Nicotiana benthamiana leaves were exposed to a sucking insect (whitefly) infestation and benzothiadiazole (BTH) for 7 d, and these exposed plants were inoculated with a tumorigenic Agrobacterium strain. We evaluated, both in planta and in vitro, how whitefly infestation affects crown gall disease. • Whitefly-infested plants exhibited at least a two-fold reduction in gall formation on both stem and crown root. Silencing of isochorismate synthase 1 (ICS1), required for salicylic acid (SA) synthesis, compromised gall formation indicating an involvement of SA in whiteflyderived plant defence against Agrobacterium. Endogenous SA content was augmented in whitefly-infested plants upon Agrobacterium inoculation. In addition, SA concentration was three times higher in root exudates from whitefly-infested plants. As a consequence, Agrobacterium-mediated transformation of roots of whitefly-infested plants was clearly inhibited when compared to control plants. These results suggest that aboveground whitefly infestation elicits systemic defence responses throughout the plant. • Our findings provide new insights into insect-mediated leaf-root intra-communication and a framework to understand interactions between three organisms: whitefly, N. benthamiana and Agrobacterium. [ABSTRACT FROM AUTHOR]

Although numerous studies have shown the ability of silicon (Si) to mitigate a wide variety of abiotic and biotic stresses, relatively little is known about the underlying mechanism(s). Here, we have investigated the role of hormone defense pathways in Si-induced resistance to the rice brown spot fungus Cochliobolus miyabeanus., To delineate the involvement of multiple hormone pathways, a multidisciplinary approach was pursued, combining exogenous hormone applications, pharmacological inhibitor experiments, time-resolved hormone measurements, and bioassays with hormone-deficient and/or -insensitive mutant lines., Contrary to other types of induced resistance, we found Si-induced brown spot resistance to function independently of the classic immune hormones salicylic acid and jasmonic acid. Our data also rule out a major role of the abscisic acid (ABA) and cytokinin pathways, but suggest that Si mounts resistance to C. miyabeanus by preventing the fungus from hijacking the rice ethylene ( ET) machinery. Interestingly, rather than suppressing rice ET signaling per se, Si probably interferes with the production and/or action of fungal ET., Together our findings favor a scenario whereby Si induces brown spot resistance by disarming fungal ET and argue that impairment of pathogen virulence factors is a core resistance mechanism underpinning Si-induced plant immunity. [ABSTRACT FROM AUTHOR]

CYP51 encodes the cytochrome P450 sterol 14α-demethylase, an enzyme essential for sterol biosynthesis and the target of azole fungicides. In Fusarium species, including pathogens of humans and plants, three CYP51 paralogues have been identified with one unique to the genus. Currently, the functions of these three genes and the rationale for their conservation within the genus Fusarium are unknown., Three Fusarium graminearum CYP51s ( Fg CYP51s) were heterologously expressed in Saccharomyces cerevisiae. Single and double Fg CYP51 deletion mutants were generated and the functions of the Fg CYP51s were characterized in vitro and in planta., Fg CYP51A and Fg CYP51B can complement yeast CYP51 function, whereas Fg CYP51C cannot. Fg CYP51A deletion increases the sensitivity of F. graminearum to the tested azoles. In ΔFg CYP51B and ΔFg CYP51 BC mutants, ascospore formation is blocked, and eburicol and two additional 14-methylated sterols accumulate. Fg CYP51C deletion reduces virulence on host wheat ears., Fg CYP51B encodes the enzyme primarily responsible for sterol 14α-demethylation, and plays an essential role in ascospore formation. Fg CYP51A encodes an additional sterol 14α-demethylase, induced on ergosterol depletion and responsible for the intrinsic variation in azole sensitivity. Fg CYP51C does not encode a sterol 14α-demethylase, but is required for full virulence on host wheat ears. This is the first example of the functional diversification of a fungal CYP51. [ABSTRACT FROM AUTHOR]

We investigated the relationship between ABA and ethylene regulating the formation of the arbuscular mycorrhiza (AM) symbiosis in tomato (Solanum lycopersicum) plants and tried to define the specific roles played by each of these phytohormones in the mycorrhization process. We analysed the impact of ABA biosynthesis inhibition on mycorrhization by Glomus intraradices in transgenic tomato plants with an altered ethylene pathway. We also studied the effects on mycorrhization in sitiens plants treated with the aminoethoxyvinyl glycine hydrochloride (AVG) ethylene biosynthesis inhibitor and supplemented with ABA. In addition, the expression of plant and fungal genes involved in the mycorrhization process was studied. ABA biosynthesis inhibition qualitatively altered the parameters of mycorrhization in accordance with the plant's ethylene perception and ethylene biosynthesis abilities. Inhibition of ABA biosynthesis in wild-type plants negatively affected all the mycorrhization parameters studied, while tomato mutants impaired in ethylene synthesis only showed a reduced arbuscular abundance in mycorrhizal roots. Inhibition of ethylene synthesis in ABA-deficient sitiens plants increased the intensity of mycorrhiza development, while ABA application rescued arbuscule abundance in the root's mycorrhizal zones. The results of our study show an antagonistic interaction between ABA and ethylene, and different roles of each of the two hormones during AM formation. This suggests that a dual ethylene-dependent / ethylene-independent mechanism is involved in ABA regulation of AM formation. [ABSTRACT FROM AUTHOR]

•Arbuscular mycorrhizal symbiosis develops in roots; extensive cellular reorganizations and specific metabolic changes occur, which are mirrored by local and systemic changes in the transcript profiles. •A TOM2 microarray ( c. 12 000 probes) has been used to obtain an overview of the transcriptional changes that are triggered in Solanum lycopersicum roots and shoots, as a result of colonization by the arbuscular mycorrhizal fungus Glomus mosseae. The cell-type expression profile of a subset of genes was monitored, using laser microdissection, to identify possible plant determinants of arbuscule development,. •Microarrays revealed 362 up-regulated and 293 down-regulated genes in roots. Significant gene modulation was also observed in shoots: 85 up- and 337 down-regulated genes. The most responsive genes in both organs were ascribed to primary and secondary metabolism, defence and response to stimuli, cell organization and protein modification, and transcriptional regulation. Six genes, preferentially expressed in arbusculated cells, were identified. •A comparative analysis only showed a limited overlap with transcript profiles identified in mycorrhizal roots of Medicago truncatula, probably as a consequence of the largely nonoverlapping probe sets on the microarray tools used. The results suggest that auxin and abscisic acid metabolism are involved in arbuscule formation and/or functioning. [ABSTRACT FROM AUTHOR]

A letter to the editor about a study on the ability of the respiratory system of ectomycorrhizal (ECM) fungi from Alaska and Pennsylvania to acclimate to temperature is presented.

The article discusses the highlights of the workshop Glomus Genome Consortium (GGC) Symposium in Nancy, France from September 16 to 17, 2008. The Joint Genome Institute (JGI) of the U.S. Department of Energy aims to study the Populus genome and its associates by creating a genomics resource for bacterial and fungal associates of the genome. The workshop was held to review that progress on the study of the Glomus genome. Among the presenters were Diederik Van Tuinen and Francis Martin of Institut National de la Recherché Agronomique (INRA).

The author investigates the biological and environmental effects of the increased emissions of biogenic volatile organic compounds (BVOCs). He says the emission rates of BVOCs increase as the temperature rise because the enzymatic activities of synthesis are enhanced. The author reveals that researchers do not know much about BVOC emissions and their responses to warming. He adds that the lack of connection between BVOC emissions and increased litter does not fit the assumption of increased emissions under increasing litter-fall.

The authors discuss how plants overcome abiotic stress through the help of their associations with symbionts and pathogens. They say the usual knowledge is that symbiotic associations are beneficial, while pathogen associations are harmful. The author reveals that reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced in both associations, meaning the plant and the microbe must be able to deal with ROS from both sides. They comment on a paper published within the issue about the beneficial aspect of plant-pathogen interactions.

• The role of abscisic acid (ABA) during the establishment of the arbuscular mycorrhiza (AM) was studied using ABA sitiens tomato ( Lycopersicon esculentum) mutants with reduced ABA concentrations. • Sitiens plants and wild-type (WT) plants were colonized by Glomus intraradices. Trypan blue and alkaline phosphatase histochemical staining procedures were used to determine both root colonization and fungal efficiency. Exogenous ABA and silver thiosulfate (STS) were applied to establish the role of ABA and putative antagonistic cross-talk between ABA and ethylene during AM formation, respectively. • Sitiens plants were less susceptible to the AM fungus than WT plants. Microscopic observations and arbuscule quantification showed differences in arbuscule morphology between WT and sitiens plants. Both ABA and STS increased susceptibility to the AM fungus in WT and sitiens plants. Fungal alkaline phosphate activity in sitiens mutants was completely restored by ABA application. • The results demonstrate that ABA contributes to the susceptibility of tomato to infection by AM fungi, and that it seems to play an important role in the development of the complete arbuscule and its functionality. Ethylene perception is crucial to AM regulation, and the impairment of mycorrhiza development in ABA-deficient plants is at least partly attributable to ethylene. [ABSTRACT FROM AUTHOR]

© New Phytologist (2003) 160: 413–420 [ABSTRACT FROM AUTHOR]

The article discusses the highlights of the August 2008 Ecological Society of America (ESA) annual meeting in Milwaukee, Wisconsin entitled Environment Fluctuation, Temporal Dynamics and Ecological Processes. The studies presented at the event showed ways of dealing with the effect of the frequencies of environmental fluctuation son the populations, the structure and the functions of ecological communities. Peter Chesson of University of Arizona described an experiment that shows the effects on herbaceous perennials of the storage effect.

• The ability of plants to adapt to multiple stresses imposed by the natural environment requires cross-talk and fine-tuning of stress signalling pathways. The hybrid histidine kinase Arabidopsis histidine kinase 5 (AHK5) is known to mediate stomatal responses to exogenous and endogenous signals in Arabidopsis thaliana. The purpose of this study was to determine whether the function of AHK5 in stress signalling extends beyond stomatal responses. • Plant growth responses to abiotic stresses, tissue susceptibility to bacterial and fungal pathogens, and hormone production and metabolism of reactive oxygen species were monitored in a T-DNA insertion mutant of AHK5. • The findings of this study indicate that AHK5 positively regulates salt sensitivity and contributes to resistance to the bacterium Pseudomonas syringae pv. tomato DC3000 and the fungal pathogen Botrytis cinerea. • This is the first report of a role for AHK5 in the regulation of survival following challenge by a hemi-biotrophic bacterium and a necrotrophic fungus, as well as in the growth response to salt stress. The function of AHK5 in regulating the production of hormones and redox homeostasis is discussed., (© 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.)

•  The mechanisms by which plant growth-promoting rhizobacteria (PGPR) mediate induced systemic resistance are currently being intensively investigated from the viewpoint of signal transduction pathways within plants. •  Here, we determined whether our well-characterized PGPR strains, which have demonstrated induced resistance on various plants, also elicit induced resistance in Arabidopsis thaliana. Nine different PGPR strains were evaluated for their capacity to cause induced resistance on Arabidopsis against two pathovars of Pseudomonas syringae. Six strains significantly reduced severity of P. syringae pv. tomato, whereas seven strains reduced severity of P. syringae pv. maculicola. •  From the initial screenings, four strains (90-166, SE34, 89B61 and T4) were selected because of their consistent induced resistance capacity. Elicitation of induced resistance with these strains depended on how disease severity was measured. Three strains (90-166, 89B61 and T4) induced resistance in NahG plants (SA-deficient), indicating a salicylic acid-independent pathway, which agrees with the previously reported pathway for induced resistance by PGPR. However, differences from the reported pathway were noted with strain 89B61, which did not require jasmonic acid or ethylene signaling pathways for induced resistance, and with strain T4, which induced resistance in npr1 plants. •  These results indicate that strains 89B61 and T4 induce resistance via a new pathway or possibly a variation of the previously reported pathway. This information will broaden our understanding of ways in which microorganisms can signal physiological changes in plants.