Arbuscular mycorrhiza (AM) represents a symbiotic mutualistic association between most land plants and Glomeromycota fungi. AM fungi develops specialized intraradical and highly branched structures, called arbuscules, where bidirectional exchange of nutrients between plant and fungi partners occurs, improving plant growth and fitness. Transcriptional reprogramming and hormonal regulation are necessary for the formation of the arbuscules. SlDLK2, a member of the third clade from the DWARF14 family of α, β-hydrolases closely related to the strigolactone receptor D14, is a negative regulator of arbuscule branching in tomato, but the underlying mechanisms are unknown. We explored the possible role of SlDLK2 on the regulation of hormonal balance. RNA-seq analysis was performed on roots from composite tomato plants overexpressing SlDLK2 and in control plants transformed with the empty vector. Analysis of transcriptomic data predicted that significantly repressed genes were enriched for genes related to hormone biosynthesis pathways, with a special relevance of carotenoid/apocarotenoid biosynthesis genes. Stable transgenic SlDLK2 overexpressing (OE) tomato lines were obtained, and hormone contents were analyzed in their roots and leaves. Interesting significant hormonal changes were found in roots of SlDLK2 OE lines with respect to the control lines, with a strong decrease on jasmonic acid and ABA. In addition, SlDLK2 OE roots showed a slight reduction in auxin contents and in one of the major strigolactones in tomato, solanacol. Overall, our results suggest that the negative regulation of AM symbiosis by SlDLK2 is associated with the repression of genes involved in the biosynthesis of AM-promoting hormones.

• Klíčová slova
• DLK2, arbuscular mycorrhiza, plant hormones, tomato, transcriptomics,
• Publikační typ
• časopisecké články MeSH

The REQUIRED FOR ARBUSCULAR MYCORRHIZATION1 (RAM1) transcription factor from the GRAS family is well known for its role as a master regulator of the arbuscular mycorrhizal (AM) symbiosis in dicotyledonous and monocotyledonous species, being essential in transcriptional reprogramming for the development and functionality of the arbuscules. In tomato, SlGRAS27 is the putative orthologue of RAM1 (here named SlRAM1), but has not yet been characterized. A reduced colonization of the root and impaired arbuscule formation were observed in SlRAM1-silenced plants, confirming the functional conservation of the RAM1 orthologue in tomato. However, unexpectedly, SlRAM1-overexpressing (UBIL:SlRAM1) plants also showed decreased mycorrhizal colonization. Analysis of non-mycorrhizal UBIL:SlRAM1 roots revealed an overall regulation of AM-related genes and a reduction of strigolactone biosynthesis. Moreover, external application of the strigolactone analogue GR244DO almost completely reversed the negative effects of SlRAM1 overexpression on the frequency of mycorrhization. However, it only partially recovered the pattern of arbuscule distribution observed in control plants. Our results strongly suggest that SlRAM1 has a dual regulatory role during mycorrhization and, in addition to its recognized action as a positive regulator of arbuscule development, it is also involved in different mechanisms for the negative regulation of mycorrhization, including the repression of strigolactone biosynthesis.

• Klíčová slova
• Arbuscular mycorrhiza, GRAS, RAM1, strigolactones, tomato, transcriptional regulation,
• MeSH
• kořeny rostlin mikrobiologie   metabolismus   genetika   MeSH
• mykorhiza * fyziologie   MeSH
• regulace genové exprese u rostlin MeSH
• rostlinné proteiny * metabolismus   genetika   MeSH
• Solanum lycopersicum * mikrobiologie   genetika   metabolismus   MeSH
• symbióza MeSH
• transkripční faktory * metabolismus   genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• rostlinné proteiny * MeSH
• transkripční faktory * MeSH

The Oryza sativa (rice) carotenoid cleavage dioxygenase OsZAS was described to produce zaxinone, a plant growth-promoting apocarotenoid. A zas mutant line showed reduced arbuscular mycorrhizal (AM) colonization, but the mechanisms underlying this behavior are unknown. Here, we investigated how OsZAS and exogenous zaxinone treatment regulate mycorrhization. Micromolar exogenous supply of zaxinone rescued root growth but not the mycorrhizal defects of the zas mutant, and even reduced mycorrhization in wild-type and zas genotypes. The zas line did not display the increase in the level of strigolactones (SLs) that was observed in wild-type plants at 7 days post-inoculation with AM fungus. Moreover, exogenous treatment with the synthetic SL analog GR24 rescued the zas mutant mycorrhizal phenotype, indicating that the lower AM colonization rate of zas is caused by a deficiency in SLs at the early stages of the interaction, and indicating that during this phase OsZAS activity is required to induce SL production, possibly mediated by the Dwarf14-Like (D14L) signaling pathway. OsZAS is expressed in arbuscule-containing cells, and OsPT11prom::OsZAS transgenic lines, where OsZAS expression is driven by the OsPT11 promoter active in arbusculated cells, exhibit increased mycorrhization compared with the wild type. Overall, our results show that the genetic manipulation of OsZAS activity in planta leads to a different effect on AM symbiosis from that of exogenous zaxinone treatment, and demonstrate that OsZAS influences the extent of AM colonization, acting as a component of a regulatory network that involves SLs.

• Klíčová slova
• Oryza sativa, OsPT11, GR24, apocarotenoids, arbuscular mycorrhizal symbiosis, in situ hybridization, strigolactones, zaxinone, zaxinone synthase,
• MeSH
• dioxygenasy * metabolismus   MeSH
• karotenoidy metabolismus   MeSH
• kořeny rostlin metabolismus   MeSH
• mykorhiza * metabolismus   MeSH
• rýže (rod) * metabolismus   MeSH
• symbióza fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• dioxygenasy * MeSH
• karotenoidy MeSH

Belowground interactions of plants with other organisms in the rhizosphere rely on extensive small-molecule communication. Chemical signals released from host plant roots ensure the development of beneficial arbuscular mycorrhizal (AM) fungi which in turn modulate host plant growth and stress tolerance. However, parasitic plants have adopted the capacity to sense the same signaling molecules and to trigger their own seed germination in the immediate vicinity of host roots. The contribution of AM fungi and parasitic plants to the regulation of phytohormone levels in host plant roots and root exudates remains largely obscure. Here, we studied the hormonome in the model system comprising tobacco as a host plant, Phelipanche spp. as a holoparasitic plant, and the AM fungus Rhizophagus irregularis. Co-cultivation of tobacco with broomrape and AM fungi alone or in combination led to characteristic changes in the levels of endogenous and exuded abscisic acid, indole-3-acetic acid, cytokinins, salicylic acid, and orobanchol-type strigolactones. The hormonal content in exudates of broomrape-infested mycorrhizal roots resembled that in exudates of infested non-mycorrhizal roots and differed from that observed in exudates of non-infested mycorrhizal roots. Moreover, we observed a significant reduction in AM colonization of infested tobacco plants, pointing to a dominant role of the holoparasite within the tripartite system.

• Klíčová slova
• mycorrhizal fungi, parasitic plants, plant hormones, rhizosphere, root exudates, small-molecule communication, strigolactones,
• MeSH
• chromatografie kapalinová MeSH
• cytokininy metabolismus   MeSH
• heterocyklické sloučeniny tricyklické metabolismus   MeSH
• hmotnostní spektrometrie MeSH
• houby fyziologie   MeSH
• interakce hostitele a patogenu MeSH
• kořeny rostlin metabolismus   mikrobiologie   MeSH
• kyselina abscisová metabolismus   MeSH
• kyselina salicylová metabolismus   MeSH
• kyseliny indoloctové metabolismus   MeSH
• laktony metabolismus   MeSH
• mykorhiza fyziologie   MeSH
• Orobanche růst a vývoj   mikrobiologie   MeSH
• tabák růst a vývoj   mikrobiologie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• cytokininy MeSH
• GR24 strigolactone MeSH Prohlížeč
• heterocyklické sloučeniny tricyklické MeSH
• indoleacetic acid MeSH Prohlížeč
• kyselina abscisová MeSH
• kyselina salicylová MeSH
• kyseliny indoloctové MeSH
• laktony MeSH

Plant roots are the first parts of plants to face drought stress (DS), and thus root modification is important for plants to adapt to drought. We hypothesized that the roots of arbuscular mycorrhizal (AM) plants exhibit better adaptation in terms of morphology and phytohormones under DS. Trifoliate orange seedlings inoculated with Diversispora versiformis were subjected to well-watered (WW) and DS conditions for 6 weeks. AM seedlings exhibited better growth performance and significantly greater number of 1st, 2nd, and 3rd order lateral roots, root length, area, average diameter, volume, tips, forks, and crossings than non-AM seedlings under both WW and DS conditions. AM fungal inoculation considerably increased root hair density under both WW and DS and root hair length under DS, while dramatically decreased root hair length under WW but there was no change in root hair diameter. AM plants had greater concentrations of indole-3-acetic acid, methyl jasmonate, nitric oxide, and calmodulin in roots, which were significantly correlated with changes in root morphology. These results support the hypothesis that AM plants show superior adaptation in root morphology under DS that is potentially associated with indole-3-acetic acid, methyl jasmonate, nitric oxide, and calmodulin levels.

• MeSH
• acetáty metabolismus   MeSH
• cyklopentany metabolismus   MeSH
• fyziologická adaptace MeSH
• Glomeromycota metabolismus   fyziologie   MeSH
• kalmodulin metabolismus   MeSH
• kořeny rostlin růst a vývoj   mikrobiologie   MeSH
• kyseliny indoloctové metabolismus   MeSH
• mykorhiza růst a vývoj   MeSH
• období sucha MeSH
• oxid dusnatý metabolismus   MeSH
• oxylipiny metabolismus   MeSH
• Poncirus růst a vývoj   mikrobiologie   MeSH
• regulátory růstu rostlin metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• acetáty MeSH
• cyklopentany MeSH
• indoleacetic acid MeSH Prohlížeč
• kalmodulin MeSH
• kyseliny indoloctové MeSH
• methyl jasmonate MeSH Prohlížeč
• oxid dusnatý MeSH
• oxylipiny MeSH
• regulátory růstu rostlin MeSH

Plant hormones have become appropriate candidates for driving functional plant mycorrhization programs, including the processes that regulate the formation of arbuscules in arbuscular mycorrhizal (AM) symbiosis. Here, we examine the role played by ABA/GA interactions regulating the formation of AM in tomato. We report differences in ABA and GA metabolism between control and mycorrhizal roots. Active synthesis and catabolism of ABA occur in AM roots. GAs level increases as a consequence of a symbiosis-induced mechanism that requires functional arbuscules which in turn is dependent on a functional ABA pathway. A negative interaction in their metabolism has been demonstrated. ABA attenuates GA-biosynthetic and increases GA-catabolic gene expression leading to a reduction in bioactive GAs. Vice versa, GA activated ABA catabolism mainly in mycorrhizal roots. The negative impact of GA3 on arbuscule abundance in wild-type plants is partially offset by treatment with ABA and the application of a GA biosynthesis inhibitor rescued the arbuscule abundance in the ABA-deficient sitiens mutant. These findings, coupled with the evidence that ABA application leads to reduce bioactive GA1, support the hypothesis that ABA could act modifying bioactive GA level to regulate AM. Taken together, our results suggest that these hormones perform essential functions and antagonize each other by oppositely regulating AM formation in tomato roots.

• Klíčová slova
• abscisic acid, arbuscular mycorrhiza, gibberellins, plant hormones, symbiosis, tomato,
• Publikační typ
• časopisecké články MeSH

Root hairs and arbuscular mycorrhiza (AM) coexist in root systems for nutrient and water absorption, but the relation between AM and root hairs is poorly known. A pot study was performed to evaluate the effects of four different AM fungi (AMF), namely, Claroideoglomus etunicatum, Diversispora versiformis, Funneliformis mosseae, and Rhizophagus intraradices on root hair development in trifoliate orange (Poncirus trifoliata) seedlings grown in sand. Mycorrhizal seedlings showed significantly higher root hair density than non-mycorrhizal seedlings, irrespective of AMF species. AMF inoculation generally significantly decreased root hair length in the first- and second-order lateral roots but increased it in the third- and fourth-order lateral roots. AMF colonization induced diverse responses in root hair diameter of different order lateral roots. Considerably greater concentrations of phosphorus (P), nitric oxide (NO), glucose, sucrose, indole-3-acetic acid (IAA), and methyl jasmonate (MeJA) were found in roots of AM seedlings than in non-AM seedlings. Levels of P, NO, carbohydrates, IAA, and MeJA in roots were correlated with AM formation and root hair development. These results suggest that AMF could alter the profile of root hairs in trifoliate orange through modulation of physiological activities. F. mosseae, which had the greatest positive effects, could represent an efficient AM fungus for increasing fruit yields or decreasing fertilizer inputs in citrus production.

• Klíčová slova
• Citrus, Glucose, IAA, MeJA, Mycorrhiza, Root hairs,
• MeSH
• biomasa MeSH
• Citrus růst a vývoj   mikrobiologie   MeSH
• Glomeromycota fyziologie   MeSH
• kořeny rostlin růst a vývoj   metabolismus   mikrobiologie   MeSH
• mykorhiza růst a vývoj   fyziologie   MeSH
• Poncirus růst a vývoj   mikrobiologie   MeSH
• půda MeSH
• půdní mikrobiologie MeSH
• semenáček růst a vývoj   metabolismus   mikrobiologie   MeSH
• symbióza fyziologie   MeSH
• výhonky rostlin růst a vývoj   metabolismus   mikrobiologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• půda MeSH