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Plant–plant interactions are a central driver for plant coexistence and community assembly. Chemically mediated plant–plant interactions are represented by allelopathy and allelobiosis. Both allelopathy and allelobiosis are achieved through specialized metabolites (allelochemicals or signaling chemicals) produced and released from neighboring plants. Allelopathy exerts mostly negative effects on the establishment and growth of neighboring plants by allelochemicals, while allelobiosis provides plant neighbor detection and identity recognition mediated by signaling chemicals. Therefore, plants can chemically affect the performance of neighboring plants through the allelopathy and allelobiosis that frequently occur in plant–plant intra-specific and inter-specific interactions. Allelopathy and allelobiosis are two probably inseparable processes that occur together in plant–plant chemical interactions. Here, we comprehensively review allelopathy and allelobiosis in plant–plant interactions, including allelopathy and allelochemicals and their application for sustainable agriculture and forestry, allelobiosis and plant identity recognition, chemically mediated root–soil interactions and plant–soil feedback, and biosynthesis and the molecular mechanisms of allelochemicals and signaling chemicals. Altogether, these efforts provide the recent advancements in the wide field of allelopathy and allelobiosis, and new insights into the chemically mediated plant–plant interactions. [ABSTRACT FROM AUTHOR]

BACKGROUND: The incidence of herbicide‐resistant barnyardgrass is escalating in paddy fields, yet the interactions between resistant weeds and rice are largely unknown. The microbiota of herbicide‐resistant barnyardgrass rhizosphere soil is critical for both barnyardgrass and rice fitness. RESULTS: Rice has different biomass allocation and root traits in the presence of penoxsulam‐resistant versus penoxsulam‐susceptible barnyardgrass or in their conditioned soil. Compared to susceptible barnyardgrass, resistant barnyardgrass led to an allelopathic increase in rice root, shoot, and whole‐plant biomasses. Resistant barnyardgrass recruited distinct core and unique microbes in rhizosphere soil compared to susceptible barnyardgrass. In particular, resistant barnyardgrass assembled more Proteobacteria and Ascomycota to enhance plant stress tolerance. Furthermore, the root exudates from resistant and susceptible barnyardgrass were responsible for the assembly and establishment of the root microbial structure. Importantly, (−)‐loliolide and jasmonic acid in root exudates were correlated with the core microbes in the rhizosphere soil. CONCLUSION: The interference of barnyardgrass with rice can be mediated by rhizosphere microbial communities. Biotype‐specific variation in the ability to generate soil microbial communities appears to ameliorate the negative consequences for rice growth, providing an intriguing possibility for modulation of the rhizosphere microbiota to increase crop productivity and sustainability. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Summary: The production of defensive metabolites in plants can be induced by signaling chemicals released by neighboring plants. Induction is mainly known from volatile aboveground signals, with belowground signals and their underlying mechanisms largely unknown.We demonstrate that (−)‐loliolide triggers defensive metabolite responses to competitors, herbivores, and pathogens in seven plant species. We further explore the transcriptional responses of defensive pathways to verify the signaling role of (−)‐loliolide in wheat and rice models with well‐known defensive metabolites and gene systems.In response to biotic and abiotic stressors, (−)‐loliolide is produced and secreted by roots. This, in turn, induces the production of defensive compounds including phenolic acids, flavonoids, terpenoids, alkaloids, benzoxazinoids, and cyanogenic glycosides, regardless of plant species. (−)‐Loliolide also triggers the expression of defense‐related genes, accompanied by an increase in the concentration of jasmonic acid and hydrogen peroxide (H2O2). Transcriptome profiling and inhibitor incubation indicate that (−)‐loliolide‐induced defense responses are regulated through pathways mediated by jasmonic acid, H2O2, and Ca 2+.These findings argue that (−)‐loliolide functions as a common belowground signal mediating chemical defense in plants. Such perception‐dependent plant chemical defenses will yield critical insights into belowground signaling interactions. See also the Commentary on this article by Frost, 238: 1749–1751. [ABSTRACT FROM AUTHOR]

Plant defense, growth, and reproduction can be modulated by chemicals emitted from neighboring plants, mainly via volatile aboveground signals. However, belowground signals and their underlying control mechanisms are largely unknown. Here, we experimentally demonstrate that the root-secreted carotenoid (–)-loliolide mediates both defensive and reproductive responses in wild-type Arabidopsis, a carotenoid-deficient Arabidopsis mutant (szl1-1), and tobacco (Nicotiana benthamiana). Wild-type Arabidopsis plants flower later than szl1-1 , and they secrete (–)-loliolide into the soil, whereas szl1-1 roots do not. When Arabidopsis and tobacco occur together, wild-type Arabidopsis induces nicotine production and defense-related gene expression in tobacco, whereas szl1-1 impairs this induction but accelerates tobacco flowering. Furthermore, nicotine production and the expression of the key genes involved in nicotine biosynthesis (QPT , PMT1), plant defense (CAT1 , SOD1 , PR-2a , PI-II , TPI), and flowering (AP1 , LFY , SOC1 , FT3 , FLC) are differently regulated by incubation with wild-type Arabidopsis and szl1-1 root exudates or (–)-loliolide. In particular, (–)-loliolide up-regulated flowering suppressors (FT3 and FLC) and transiently down-regulated flowering stimulators (AP1 and SOC1), delaying tobacco flowering. Therefore, root-secreted (–)-loliolide modulates plant belowground defense and aboveground flowering, yielding critical insights into plant–plant signaling interactions. [ABSTRACT FROM AUTHOR]

Summary: Plants actively respond to their neighbors by altering root placement patterns. Neighbor‐modulated root responses involve root detection and interactions mediated by root‐secreted functional metabolites. However, chemically mediated root placement patterns and their underlying mechanisms remain elusive.We used an allelopathic wheat model system challenged with 60 target species to identify root placement responses in window rhizobox experiments. We then tested root responses and their biochemical mechanisms in incubation experiments involving the addition of activated carbon and functional metabolites with amyloplast staining and auxin localization in roots.Wheat and each target species demonstrated intrusive, avoidant or unresponsive root placement, resulting in a total of nine combined patterns. Root placement patterns were mediated by wheat allelochemicals and (–)‐loliolide signaling of neighbor species. In particular, (–)‐loliolide triggered wheat allelochemical production that altered root growth and placement, degraded starch grains in the root cap and induced uneven distribution of auxin in target species roots.Root placement patterns in wheat–neighbor interactions were perception dependent and species dependent. Signaling (−)‐loliolide induced the production and release of wheat allelochemicals that modulated root placement patterns. Therefore, root placement patterns are generated by both signaling chemicals and allelochemicals in allelopathic plant–plant interactions. [ABSTRACT FROM AUTHOR]

Plant‐to‐plant signalling is a key mediator of interactions among plant species. Plants can perceive and respond to chemical cues emitted from their neighbours, altering survival and performance, impacting plant coexistence and community assembly. An increasing number of studies indicate root exudates as key players in plant‐to‐plant signalling. Root exudates mediate root detection and behaviour, kin recognition, flowering and production, driving inter‐ and intra‐specific facilitation in cropping systems and mixed‐species plantations. Altered interactions may be attributed to the signalling components within root exudates. Root ethylene, strigolactones, jasmonic acid, (‐)‐loliolide and allantoin are signalling chemicals that convey information on local conditions in plant–plant interactions. These root‐secreted signalling chemicals appear ubiquitous in plants and trigger a series of belowground responses inter‐ and intra‐specifically, involving molecular events in biosynthesis, secretion and action. The secretion of root signals, mainly mediated by ATP‐binding cassette transporters, is critical. Root‐secreted signalling chemicals and their molecular mechanisms are rapidly revealing a multitude of fascinating plant–plant interactions. However, many root signals, particularly species‐specific signals and their underlying mechanisms, remain to be uncovered due to methodological limitations and root‐soil interactions. A thorough understanding of root‐secreted chemical signals and their mechanisms will offer many ecological implications and potential applications for sustainable agriculture. This review deals with the roles of root exudates in plant‐to‐plant signalling, and the identity of root‐secreted chemical signals and their molecular mechanisms, providing fascinating insights into communication and interactions among plants. [ABSTRACT FROM AUTHOR]

Neighbor detection and allelochemical response are important mediators in plant–plant interactions. Although there is increasing knowledge about plant allelochemicals released in response to the presence of competitors and involved in neighbor-derived signaling, less is known about which signaling chemicals are responsible for the neighbor-induced allelochemical response. Here, we experimentally demonstrate that (–)-loliolide, a carotenoid metabolite, acts as a signaling chemical in barnyardgrass–rice allelopathic interactions. The production of the rice allelochemicals momilactone B and tricin was increased in the presence of five biotypes of barnyardgrass. (–)-Loliolide was found in all the biotypes of barnyardgrass and their root exudates and rhizosphere soils. There were significant positive relationships between rice allelochemicals and (–)-loliolide concentrations across the biotypes of barnyardgrass. Furthermore, (–)-loliolide elicited the production of momilactone B and tricin. Comparative transcriptomic analysis revealed regulatory activity of (–)-loliolide on the diterpenoid and flavonoid biosynthesis pathway. The expression of key genes involved in the biosynthesis of momilactone B (CPS4 , KSL4 , and MAS) and tricin (CYP75B3 and CYP75B4) was up-regulated by (–)-loliolide. These findings suggest that (–)-loliolide acts as a signaling chemical and participates in barnyardgrass-rice allelopathic interactions. Allelopathic rice plants can detect competing barnyardgrass through the presence of this signaling chemical and respond by increasing levels of their allelochemicals to achieve an advantage for their own growth. [ABSTRACT FROM AUTHOR]

BACKGROUND To develop a coumarin-based fungicide, a series of 3-benzoyl-4-hydroxylcoumarin derivatives were synthesised and their fungicidal activities were evaluated against typical fungi occurring in Chinese agroecosystems. RESULTS Target compounds were characterised through 1H NMR, 13C NMR and high-resolution mass spectrometry. The crystal structure of compound III-21 was determined through X-ray diffraction. Bioassay results indicated that most of the target compounds showed good growth inhibition against all of the fungi tested in vitro. EC50 of the target compounds against Physalospora piricola, Rhizoctonia cerealis, Sclerotinia sclerotiorum and Botrytis cinerea indicated that most of the target compounds displayed comparable activity with that of carbindazim and chlorothalonil in vitro. Among these compounds, the analogue 3-(2-bromo-4-chlorobenzoyl)-4-hydroxylcoumarin ( III-21) displayed the optimum growth inhibition against R. cerealis (87.5%) and B. cinerea (82.7%) in vivo at 200 µg mL−1 concentration; thus, this analogue is a potential inhibitor of pathogenic fungi and a new major compound for further optimisation. The results of analysing the structure-activity relationships demonstrated that changes in substituents on benzene ring A of 3-benzoyl-4-hydroxylcoumarin caused different fungicidal activities and provided original information on the preferential conformation to maintain high activities. CONCLUSION The present work demonstrated that 3-benzoyl-4-hydroxylcoumarin derivatives can be used as possible major compounds to develop novel fungicides. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND: Interference of allelopathic wheat with weeds involves a broad spectrum of species either independently or synergistically with competitive factors. This study examined the interference of allelopathic wheat with 38 weeds in relation to the production of allelochemical 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) in wheat with and without root-root interactions. RESULTS: There were substantial differences in weed biomass and DIMBOA concentration in wheat-weed coexisting systems. Among 38 weeds, nineweedswere inhibited significantly by allelopathic wheat but the other 29 weedswere not.DIMBOA levels in wheat varied greatlywith weed species. Therewas no significant relationship between DIMBOA levels and weed suppression effects. Root segregation led to great changes inweed inhibition and DIMBOA level. Comparedwith root contact, the inhibition of eightweedswas loweredsignificantly, while significantly increased inhibition occurredin 11weedswith anincreasedDIMBOA concentration under root segregation. Furthermore, the production of DIMBOA in wheatwas induced by the root exudates from weeds. CONCLUSION: Interference of allelopathic wheat with weeds not only is determined by the specificity of the weeds but also depends on root-root interactions. In particular, allelopathic wheat may detect certain weeds through the root exudates and respond by increasing the allelochemical, resulting in weed identity recognition. [ABSTRACT FROM AUTHOR]