Unraveling the Initial Plant Hormone Signaling, Metabolic Mechanisms and Plant Defense Triggering the Endomycorrhizal Symbiosis Behavior

Abstract

Arbuscular mycorrhizal (AM) fungi establish probably one of the oldest mutualistic relationships with the roots of most plants on earth. The wide distribution of these fungi in almost all soil ecotypes and the broad range of host plant species demonstrate their strong plasticity to cope with various environmental conditions. AM fungi elaborate fine-tuned molecular interactions with plants that determine their spread within root cortical tissues. Interactions with endomycorrhizal fungi can bring various benefits to plants, such as improved nutritional status, higher photosynthesis, protection against biotic and abiotic stresses based on regulation of many physiological processes which participate in promoting plant performances. In turn, host plants provide a specific habitat as physical support and a favorable metabolic frame, allowing uptake and assimilation of compounds required for the life cycle completion of these obligate biotrophic fungi. The search for formal and direct evidences of fungal energetic needs raised strong motivated projects since decades, but the impossibility to produce AM fungi under axenic conditions remains a deep enigma and still feeds numerous debates. Here, we review and discuss the initial favorable and non-favorable metabolic plant context that may fate the mycorrhizal behavior, with a focus on hormone interplays and their links with mitochondrial respiration, carbon partitioning and plant defense system, structured according to the action of phosphorus as a main limiting factor for mycorrhizal symbiosis. Then, we provide with models and discuss their significances to propose metabolic targets that could allow to develop innovations for the production and application of AM fungal inocula.

Peer Review #2 of "Distinct gene expression and secondary metabolite profiles in suppressor of prosystemin-mediated responses2 (spr2) tomato mutants having impaired mycorrhizal colonization (v0.1)"

“…Manuscript to be reviewed was dependent on factors such as genotype and colonization time. They also agreed partially with the concept that AMF colonization efficiency involves changes in the content of several categories of lipids (see above), including lysophospholipids, in addition to phytosteroids (see below), carotenes, phenolic compounds, polyamines, auxins, cytokinins, amino acids and other nitrogencontaining compounds (Akiyama and Hayashi, 2006;Drissner et al, 2007;Floss et al, 2008bFloss et al, , 2009Whiteside et al, 2012;Jiménez-Bremont et al, 2014;Rivero et al, 2015;Bedini et al, 2018;Sánchez-Bel et al, 2018;Liao et al, 2018).…”

“…Manuscript to be reviewed corroborated the above mentioned notion that SA acts as an inhibitor of the mycorrhizal symbiosis (Blilou et al, 1999;Herrera-Medina et al, 2003;Bedini et al, 2018).…”

“…A similar argument could explain the significantly higher level of PO 4 3in leaves of mycorrhizal WT leaves. On the other hand, significantly higher content of DL-malic acid and L-threonic acid in spr2 roots deficient in mycorrhizal colonization could have mirrored a metabolic condition not amenable to AMF colonization (Bedini et al, 2018). With respect to the SA-dependent implementation of the AMFinhibiting SAR described above, it is germane to add that SA is also believed to involve a repression of fermentation, higher cytosolic oxidative potential and other conditions known to favor AMF colonization (Bedini et al, 2018).…”

“…Another possible drawback was that the effect on AMF colonization was revealed only after BR levels were severely reduced (Foo et al, 2013). This scenario reflects the paucity of information regarding the precise role played by BRs during the AMF colonization process (Bedini et al, 2018;McGuiness et al, 2019).…”

Phytohormonal cross-talk modulate Bipolaris sorokiniana (Scc.)interaction with Zea mays

“…Pea mutant cry-s is known to have high AF colonization due to reduce level of GA 3 and high DELLA protein activity (McGuiness et al, 2019). Fungal sporulation specifically needs low GA signalling in host as an optimal environment (Bedini et al, 2018). The plant host usually discourages the biotroph growth in their tissues by releasing GA 3 and associated signalling with it (Yimer et al, 2018).…”