Given the large yield losses attributed to plant-parasitic nematodes and the limited availability of sustainable control strategies, new plant-parasitic nematode control strategies are urgently ...needed. To defend themselves against nematode attack, plants possess sophisticated multi-layered immune systems. One element of plant immunity against nematodes is the production of small molecules with anti-nematode activity, either constitutively or after nematode infection. This review provides an overview of such metabolites that have been identified to date and groups them by chemical class (e.g., terpenoids, flavonoids, glucosinolates, etc.). Furthermore, this review discusses strategies that have been used to identify such metabolites and highlights the ways in which studying anti-nematode metabolites might be of use to agriculture and crop protection. Particular attention is given to emerging, high-throughput approaches for the identification of anti-nematode metabolites, in particular the use of untargeted metabolomics techniques based on nuclear magnetic resonance (NMR) and mass spectrometry (MS).
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.
Significance We communicate the rather remarkable observation that among 291 tested accessions of cultivated sweet potato, all contain one or more transfer DNA (T-DNA) sequences. These sequences, ...which are shown to be expressed in a cultivated sweet potato clone (“Huachano”) that was analyzed in detail, suggest that an Agrobacterium infection occurred in evolutionary times. One of the T-DNAs is apparently present in all cultivated sweet potato clones, but not in the crop’s closely related wild relatives, suggesting the T-DNA provided a trait or traits that were selected for during domestication. This finding draws attention to the importance of plant–microbe interactions, and given that this crop has been eaten for millennia, it may change the paradigm governing the “unnatural” status of transgenic crops.
Agrobacterium rhizogenes and Agrobacterium tumefaciens are plant pathogenic bacteria capable of transferring DNA fragments transfer DNA (T-DNA) bearing functional genes into the host plant genome. This naturally occurring mechanism has been adapted by plant biotechnologists to develop genetically modified crops that today are grown on more than 10% of the world’s arable land, although their use can result in considerable controversy. While assembling small interfering RNAs, or siRNAs, of sweet potato plants for metagenomic analysis, sequences homologous to T-DNA sequences from Agrobacterium spp. were discovered. Simple and quantitative PCR, Southern blotting, genome walking, and bacterial artificial chromosome library screening and sequencing unambiguously demonstrated that two different T-DNA regions ( Ib T-DNA1 and Ib T-DNA2) are present in the cultivated sweet potato ( Ipomoea batatas L. Lam.) genome and that these foreign genes are expressed at detectable levels in different tissues of the sweet potato plant. Ib T-DNA1 was found to contain four open reading frames (ORFs) homologous to the tryptophan-2-monooxygenase ( iaaM ), indole-3-acetamide hydrolase ( iaaH ), C-protein ( C-prot ), and agrocinopine synthase ( Acs ) genes of Agrobacterium spp. Ib T-DNA1 was detected in all 291 cultigens examined, but not in close wild relatives. Ib T-DNA2 contained at least five ORFs with significant homology to the ORF14 , ORF17n , rooting locus ( Rol ) B/RolC , ORF13 , and ORF18/ORF17n genes of A. rhizogenes . Ib T-DNA2 was detected in 45 of 217 genotypes that included both cultivated and wild species. Our finding, that sweet potato is naturally transgenic while being a widely and traditionally consumed food crop, could affect the current consumer distrust of the safety of transgenic food crops.
Complex defense signaling pathways, controlled by different hormones, are involved in the reaction of plants to a wide range of biotic and abiotic stress factors. We studied the ability of salicylic ...acid, jasmonate (JA), and ethylene (ET) to induce systemic defense in rice (Oryza sativa) against the root knot nematode Meloidogyne graminicola. Exogenous ET (ethephon) and JA (methy1 jasmonate) supply on the shoots induced a strong systemic defense response in the roots, exemplified by a major up-regulation of pathogenesis-related genes OsPR1a and OsPR1b, while the salicylic acid analog BTH (benzo-1,2,3-thiadiazole-7-carbothioic acid S-methy1 ester) was a less potent systemic defense inducer from shoot to root. Experiments with JA biosynthesis mutants and ET-insensitive transgenics showed that ET-induced defense requires an intact JA pathway, while JA-induced defense was still functional when ET signaling was impaired. Pharmacological inhibition of JA and ET biosynthesis confirmed that JA biosynthesis is needed for ET-induced systemic defense, and quantitative real-time reverse transcription-polymerase chain reaction data revealed that ET application onto the shoots strongly activates JA biosynthesis and signaling genes in the roots. All data provided in this study point to the JA pathway to play a pivotal role in rice defense against root knot nematodes. The expression of defense-related genes was monitored in root galls caused by M. graminicola. Different analyzed defense genes were attenuated in root galls caused by the nematode at early time points after infection. However, when the exogenous defense inducers ethephon and methy1 jasmonate were supplied to the plant, the nematode was less effective in counteracting root defense pathways, hence making the plant more resistant to nematode infection.
To be protected from biological threats, plants have evolved an immune system comprising constitutive and inducible defenses. For example, upon perception of certain stimuli, plants can develop a ...conditioned state of enhanced defensive capacity against upcoming pathogens and pests, resulting in a phenotype called ‘induced resistance’ (IR). To tackle the confusing lexicon currently used in the IR field, we propose a widely applicable code of practice concerning the terminology and description of IR phenotypes using two main phenotypical aspects: local versus systemic resistance, and direct versus primed defense responses. Our general framework aims to improve uniformity and consistency in future scientific communication, which should help to avoid further misinterpretations and facilitate the accessibility and impact of this research field.
Upon perception of certain stimuli, plants can develop a conditioned state of enhanced defensive capacity against upcoming pathogens and pests, resulting in a phenotype called ‘induced resistance’ (IR).Scientific communication in the IR research domain is flawed with inconsistent use of various conceptualizations and terms.Researchers working on non-model organisms and/or less-studied plant tissues – which often make use of distinct natural defense mechanisms – are struggling to choose the correct term for their observations.Different biological and chemical IR stimuli tend to induce resistance through various pathways and hence terminology can and should not be linked to underlying mechanisms.
The nonprotein amino acid β-aminobutyric acid (BABA) is known to protect plants against various pathogens. The mode of action is relatively diverse and specific in different plant-pathogen systems. ...To extend the analysis of the mode of action of BABA to plant-parasitic nematodes in monocot plants, we evaluated the effect of BABA against the root-knot nematode (RKN) Meloidogyne graminicola in rice. BABA treatment of rice plants inhibited nematode penetration and resulted in delayed nematode and giant cell development. BABA-induced resistance (BABA-IR) was still functional in mutants or transgenics defective in salicylic acid biosynthesis and response or abscisic acid (ABA) response. Pharmacological inhibition of jasmonic acid (JA) and ethylene (ET) biosynthesis indicated that BABA-IR against rice RKN likely occurs independent of JA and ET. However, histochemical and biochemical quantification in combination with quantitative real-time reverse transcription-polymerase chain reaction data suggest that BABA protects rice against RKN through the activation of basal defense mechanisms of the plant, such as reactive oxygen species accumulation, lignin formation, and callose deposition.
Small RNAs (sRNAs) regulate numerous plant processes directly related to yield, such as disease resistance and plant growth. To exploit this yield-regulating potential of sRNAs, the sRNA profile of ...one of the world's most important staple crops - rice - was investigated throughout plant development using next-generation sequencing.
Root and leaves were investigated at both the vegetative and generative phase, and early-life sRNA expression was characterized in the embryo and endosperm. This led to the identification of 49,505 novel sRNAs and 5581 tRNA-derived sRNAs (tsRNAs). In all tissues, 24 nt small interfering RNAs (siRNAs) were highly expressed and associated with euchromatic, but not heterochromatic transposable elements. Twenty-one nt siRNAs deriving from genic regions in the endosperm were exceptionally highly expressed, mimicking previously reported expression levels of 24 nt siRNAs in younger endosperm samples. In rice embryos, sRNA content was highly diverse while tsRNAs were underrepresented, possibly due to snoRNA activity. Publicly available mRNA expression and DNA methylation profiles were used to identify putative siRNA targets in embryo and endosperm. These include multiple genes related to the plant hormones gibberellic acid and ethylene, and to seed phytoalexin and iron content.
This work introduces multiple sRNAs as potential regulators of rice yield and quality, identifying them as possible targets for the continuous search to optimize rice production.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This article comments on:
Noureddine Y, da Rocha M, An J, Médina C, Mejias J, Mulet K, Quentin M, Abad P, Zouine M, Favery B, Jaubert-Possamai S. 2023. AUXIN RESPONSIVE FACTOR8 regulates development ...of the feeding site induced by root-knot nematodes in tomato. Journal of Experimental Botany 74, 5752–5766.
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.