Enhancing arbuscular mycorrhiza symbiosis effectiveness through the involvement of the tomato GRAS transcription factor SCL3/SlGRAS18

Arbuscular mycorrhizal (AM) fungi improve plant growth, nutrition, fitness and stress tolerance while AM fungi obtain carbohydrates and lipids from the host. This whole process of mutual benefit requires substantial alterations in the structural and functional aspects of the host root cells. These modifications ultimately culminate in the formation of arbuscules, which are specialized intraradical and highly branched fungal structures. Arbuscule-containing cells undergo massive reprogramming to hosting arbuscule and members of the GRAS transcription factor family have been characterized as AM inducible genes which play a pivotal role in these process. Here, we show a functional analysis for the GRAS transcription factor SCL3/SlGRAS18 in tomato. SlGRAS18 interacts with SlDELLA, a central regulator of AM formation. Silencing of SlGRAS18 positively impacts arbuscule development and the improvement in symbiotic status, favouring flowering and therefore progress in the formation and development of fruits in SlGRAS18 silenced plants which parallel to a discernible pattern of mineral nutrient redistribution in leaves. Our results advance the knowledge of GRAS transcription factors involved in the formation and establishment of AM symbiosis and provide experimental evidence for how specific genetic alterations can lead to more effective AM symbiosi

Identification and Expression Analysis of GRAS Transcription Factor Genes Involved in the Control of Arbuscular Mycorrhizal Development in Tomato

The formation and functioning of arbuscular mycorrhizal (AM) symbiosis are complex and tightly regulated processes. Transcriptional regulation mechanisms have been reported to mediate gene expression changes closely associated with arbuscule formation, where nutrients move between the plant and fungus. Numerous genes encoding transcription factors (TFs), with those belonging to the GRAS family being of particular importance, are induced upon mycorrhization. In this study, a screening for candidate transcription factor genes differentially regulated in AM tomato roots showed that more than 30% of known GRAS tomato genes are upregulated upon mycorrhization. Some AM-upregulated GRAS genes were identified as encoding for transcription factors which are putative orthologs of previously identified regulators of mycorrhization in other plant species. The symbiotic role played by other newly identified AM-upregulated GRAS genes remains unknown. Preliminary results on the involvement of tomato SlGRAS18, SlGRAS38, and SlGRAS43 from the SCL3, SCL32, and SCR clades, respectively, in mycorrhization are presented. All three showed high transcript levels in the late stages of mycorrhization, and the analysis of promoter activity demonstrated that SlGRAS18 and SlGRAS43 are significantly induced in cells containing arbuscules. When SlGRAS18 and SlGRAS38 genes were silenced using RNA interference in hairy root composite tomato plants, a delay in mycorrhizal infection was observed, while an increase in mycorrhizal colonization was observed in SlGRAS43 RNAi roots. The possible mode of action of these TFs during mycorrhization is discussed, with a particular emphasis on the potential involvement of the SHR/SCR/SCL3 module of GRAS TFs in the regulation of gibberellin signaling during mycorrhization, which is analogous to other plant developmental processes

Analysis of overexpression and silencing of gras transcription factor gene GRAS38 in arbuscular mycorrhizal tomato plants.

Resumen del poster presentado en: XVI Reunión de Biología Molecular de Plantas. Sevilla, 14-16 septiembre (2022

Analysis of silencing of gras transcription factor gene GRAS18 in arbuscular mycorrhizal tomato plants.

Resumen del poster presentado en: XVI Meeting of Plant Molecular Biology - XVI Reunión de Biología Molecular de Plantas. Sevilla 14-16 Septiembre (2022

Identification and expression analysis of the arbuscular mycorrhiza-inducible Rieske non-heme oxygenase Ptc52 gene from tomato

Arbuscular mycorrhizal (AM) formation enhances plant growth and fitness through improved uptake of water and mineral nutrients in exchange for carbon compounds to the AM fungus. The fungal structure for the reciprocal exchange of nutrients in the symbiosis is the arbuscule, and defence genes expressed in cells containing arbuscules could play a role in the control of hyphal spread and arbuscule formation in the root. We characterized and analyzed the Ptc52 gene from tomato (SlPtc52), a member of the gene family of non-heme oxygenases, whose function has been related to the lethal leaf spot 1 (Lls1) lesion mimic phenotype in plants which is sometimes associated with enhanced disease resistance. Sequence analysis of the SlPTC52 protein revealed conserved typical motifs from non-heme oxygenases, including a Rieske [2Fe-2S] motif, a mononuclear non-heme iron-binding motif and a C-terminal CxxC motif. The level of transcript accumulation was low in stem, flower and green fruits, and high in leaves. Although SlPtc52 expression was perceptible at low levels in roots, its expression increased concomitantly with AM fungus root colonization. Tomato non-mycorrhizal hairy roots expressing the GUS protein under the control of promoter SlPtc52 exhibited GUS activity in the endodermis, the apical meristem of the root tip and in the lateral root primordium. AM fungal colonization also resulted in intensive GUS activity that clearly corresponds to cortical cells containing arbuscules. SlPtc52 gene silencing led to a delay in root colonization and a decrease in arbuscular abundance, suggesting that SlPTC52 plays a regulatory role during AM symbiosis.We wish to thank the Tomato Genetics Resource Centre (TGRC) of the University of California for providing the tomato seeds. This study was supported by grants from the Interministerial Commission of Science and Technology (CICYT) and the European Regional Development Fund (FEDER) through the Spanish Ministry of the Economy and Competitiveness (AGL2014-52298-P; AGL2017-83871-P). J.A. Martín Rodríguez was supported by a research fellowship from the FPU-MICINN program. We also wish to thank Michael O’Shea for proofreading the manuscript.Peer Reviewe

Ethylene alleviates the suppressive effect of phosphate on arbuscular mycorrhiza formation

Phosphorus is one of the most important macronutrients required for plant growth. Plants have evolved many strategies for inorganic phosphorus (Pi) acquisition, including the symbiotic pathways, involving the formation of mycorrhiza. With regard to arbuscular mycorrhiza (AM), high Pi availability has long been known to negatively affect this association, although the underlying mechanism is unknown. In the present study, the interactive role played by ethylene and Pi in AM regulation was investigated in the tomato-Rhizophagus irregularis symbiosis. AM fungal colonization was analysed in epi, rin and NRO ethylene-responsive mutants under different Pi availability conditions, with a focus on the late stages of the interaction. Although Pi inhibited mycorrhizal parameters in the ethylene-insensitive rin mutant and wild-type cultivars, it did not alter the mycorrhization of the epi tomato mutant, which exhibits a constitutive ethylene-induced response. As with the colonization parameters, root ethylene content and the expression of AM-related and ethylene receptor 6 genes were inhibited by Pi in wild-type cultivars and rin mutants, but were unaffected or slightly activated in epi plants. The application of ethephon offsets the negative impact on the mycorrhizal development caused by the application of Pi. This compensation effect is dose dependent and was ineffective in the NRO mutant, which is more insensitive to the action of ethylene. Our results provide evidence that ethylene signalling negatively affects the suppressive effect of Pi on AM formation and suggests an overlap between this suppressive effect and the regulatory mechanism of Pi-starvation response pathway in plants mediated by ethylene.This study was supported by grants from the Comisión Interministerial de Ciencia y Tecnología (CICYT) and the European Regional Development Fund (ERDF) through the Ministerio de Economía y Competitividad in Spain (AGL2011-25930; AGL2014-52298-P) as well as the Junta de Andalucía (Research Group BIO 260). We wish to thank the Tomato Genetics Resource Centre (TGRC) of the University of California for providing tomato seeds. We would also like to thank Michael O’Shea for proof-reading the document. R Torres de los Santos was supported by the Carolina foundation.Peer Reviewe

Transcriptional regulation of Arbuscular Mycorrhiza in tomato by GRAS transcription factors

Resumen del poster presentado en: iMMM2023. 6th International Molecular Mycorrhiza Meeting. 90 (2023

Transcriptional regulation of Arbuscular Mycorrhiza by GRAS transcription factors

1 página - Poster presentado en Iberian Plant Biology 2023. XVIII Portuguese-Spanish Congress on Plant Biology and the XXV Meeting of the Spanish Society of Plant Biology. 9-12 Julio 2023, Braga, Portugal

The SlDLK2 receptor involved in the control of arbuscular mycorrhizal symbiosis regulates hormonal balance

Poster presentado en: XVI Congreso de Fitohormonas: Metabolismo y Modo de Acción. Segovia, España. 19-21 abril (2023

Transcriptional regulation of Arbuscular Mycorrhiza by GRAS transcription factors

1 página - Poster presentado en Iberian Plant Biology 2023. XVIII Portuguese-Spanish Congress on Plant Biology and the XXV Meeting of the Spanish Society of Plant Biology. 9-12 Julio 2023, Braga, Portugal