Climate changes include the intensification of drought in many parts of the world, increasing its frequency, severity and duration. However, under natural conditions, environmental stresses do not occur alone, and, in addition, more stressed plants may become more susceptible to attacks by pests and pathogens. Studies on the impact of the arbuscular mycorrhizal (AM) symbiosis on tomato response to water deficit showed that several drought-responsive genes are differentially regulated in AM-colonized tomato plants (roots and leaves) during water deficit. To date, global changes in mycorrhizal tomato root transcripts under water stress conditions have not been yet investigated. Here, changes in root transcriptome in the presence of an AM fungus, with or without water stress (WS) application, have been evaluated in a commercial tomato cultivar already investigated for the water stress response during AM symbiosis. Since root-knot nematodes (RKNs, Meloidogyne incognita ) are obligate endoparasites and cause severe yield losses in tomato, the impact of the AM fungal colonization on RKN infection at 7 days post-inoculation was also evaluated. Results offer new information about the response to AM symbiosis, highlighting a functional redundancy for several tomato gene families, as well as on the tomato and fungal genes involved in WS response during symbiosis, underlying the role of the AM fungus. Changes in the expression of tomato genes related to nematode infection during AM symbiosis highlight a role of AM colonization in triggering defense responses against RKN in tomato. Overall, new datasets on the tomato response to an abiotic and biotic stress during AM symbiosis have been obtained, providing useful data for further researches.
A study was carried out on the effect of the root endophytic fungus Pochonia chlamydosporia on plant systemic signal of defense related genes during fungal or nematode parasitism. Different biotic stress factors were examined, inoculating roots of dicot and monocot hosts with the endophyte, and measuring the expression of defense genes in leaves. A first greenhouse assay was carried out on expression of PAL, PIN II, PR1 and LOX D in leaves of tomato cv Tondino inoculated with Phytophthora infestans (CBS 120920), inoculating or not the roots of infected plants with P. chlamydosporia DSM 26985. In a second assay, plants of banana (Musa acuminata cv Grand Naine) were artificially infected with Fusarium oxysporum f. sp. cubense Tropical race 4 (TR4) and inoculated or not with DSM 26985. In a further experiment, banana plants were inoculated or not with P. chlamydosporia plus juveniles of the root knot nematode (RKN) Meloidogyne incognita. A similar assay was also carried out in vitro with adults and juveniles of the lesion nematode Pratylenchus goodeyi. Differential expression of the defense genes examined was observed for all plant-stress associations, indicative of early, upward systemic signals induced by the endophyte. Changes in expression profiles included a 5-fold down-regulation of PIN II at 2 dai in leaves of tomato plants treated with P. infestans and/or P. chlamydosporia, and the up-regulation of PAL by the endophyte alone, at 2 and 7 dai. In the TR4 assay, PR1 was significantly up-regulated at 7 dai in banana leaves, but only in the P. chlamydosporia treated plants. At 10 dai, PIN II expression was significantly higher in leaves of plants inoculated only with TR4. The banana-RKN assay showed a PR1 expression significantly higher than controls at 4 and 7 dai in plants inoculated with P. chlamydosporia alone, and a down-regulation at 4 dai in leaves of plants also inoculated with RKN, with a PR1 differential up-regulation at 10 dai. Pratylenchus goodeyi down-regulated PIN at 21 dai, with or without the endophyte, as well as PAL but only in presence of P. chlamydosporia. When inoculated alone, the endophyte up-regulated PR1 and LOX. The gene expression patterns observed in leaves suggest specific and time-dependent relationships linking host plants and P. chlamydosporia in presence of biotic stress factors, functional to a systemic, although complex, activation of defense genes.
The molecular mechanisms active during the endophytic phase of the fungus Pochonia chlamydosporia are still poorly understood. In particular, few data are available on the links between the endophyte and the root response, as modulated by noncoding small RNAs. In this study, we describe the microRNAs (miRNAs) that are differentially expressed (DE) in the roots of tomato, colonized by P. chlamydosporia. A genome-wide NGS expression profiling of small RNAs in roots, either colonized or not by the fungus, showed 26 miRNAs upregulated in inoculated roots. Their predicted target genes are involved in the plant information processing system, which recognizes, percepts, and transmits signals, with higher representations in processes such as apoptosis and plant defense regulation. RNAseq data showed that predicted miRNA target genes were downregulated in tomato roots after 4, 7, 10, and 21 days post P. chlamydosporia inoculation. The differential expression of four miRNAs was further validated using qPCR analysis. The P. chlamydosporia endophytic lifestyle in tomato roots included an intricate network of miRNAs and targets. Data provide a first platform of DE tomato miRNAs after P. chlamydosporia colonization. They indicated that several miRNAs are involved in the host response to the fungus, playing important roles for its recognition as a symbiotic microorganism, allowing endophytism by modulating the host defense reaction. Data also indicated that endophytism affects tRNA fragmentation. This is the first study on miRNAs induced by P. chlamydosporia endophytism and related development regulation effects in Solanum lycopersicum.
In vitro assays were performed under varying nutritional conditions to investigate the expression of four genes of the fungus Pochonia chlamydosporia, a nematode parasite and a plant growth promoter. The expression levels of a basic leucine zipper (bZIP) transcription factor, a putative phytase, a phospholipase D (PLD) and a monoxygenase of isolate DSM 26985 were, after 8 h incubation in the presence of Meloidogyne incognita eggs, 3, 14, 900 and 67-fold higher than the fungus alone, respectively. M. incognita uninoculated tomato plants alone induced, at 4 h incubation, a phytase transcription sixfold higher than control. Changes in transcript amounts were not significant when the fungus was in the presence of nematode parasitized plants. Further assays performed at different pHs or in the presence of glucose and NH 4 + showed that the bZIP and phytase transcripts reflect early changes in the fungus metabolism. Barley plants treated with P. chlamydosporia isolates IMI 331547 and DSM 26985 showed a pronounced plant growth promotion effect of the former isolate. Phytic acid affected growth of isolates at 1 × 10 −4 ppm concentration, however, the colony diameter increased at 10 ppm. Gene expression data showed that P. chlamydosporia metabolism reflects key biochemical signals proceeding from roots and host nematode eggs.
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