Abstract
Morphotypes of arbuscular mycorrhizal (AM) symbiosis, Arum, Paris, and Intermediate types, are mainly determined by host plant lineages. It was reported that the phytohormone gibberellin (GA) inhibits the establishment of Arum-type AM symbiosis in legume plants. In contrast, we previously reported that GA promotes the establishment of Paris-type AM symbiosis in Eustoma grandiflorum, while suppressing Arum-type AM symbiosis in a legume model plant, Lotus japonicus. This raises a hitherto unexplored possibility that GA-mediated transcriptional reprogramming during AM symbiosis is different among plant lineages as the AM morphotypes are distinct. Here, our comparative transcriptomics revealed that several symbiosis-related genes were commonly upregulated upon AM fungal colonization in L. japonicus (Arum-type), Daucus carota (Intermediate-type), and E. grandiflorum (Paris-type). Despite of the similarities, the fungal colonization levels and the expression of symbiosis-related genes were suppressed in L. japonicus and D. carota but were promoted in E. grandiflorum in the presence of GA. Moreover, exogenous GA inhibited the expression of genes involved in biosynthetic process of the pre-symbiotic signal component, strigolactone, which resulted in the reduction of its endogenous accumulation in L. japonicus and E. grandiflorum. Additionally, differential regulation of genes involved in sugar metabolism suggested that disaccharides metabolized in AM roots would be different between L. japonicus and D. carota/E. grandiflorum. Therefore, this study uncovered the conserved transcriptional responses during mycorrhization regardless of the distinct AM morphotype. Meanwhile, we also found diverse responses to GA among phylogenetically distant AM host plants.
Highlights
More than 70% of terrestrial plants associate with the symbiotic, arbuscular mycorrhizal (AM) fungi that belong to Glomeromycotina (Brundrett and Tedersoo, 2018)
We identified ortholog genes in L. japonicus, D. carota, and E. grandiflorum to compare the influence of AM fungal colonization and GA treatment among these different host species
A set of known AM symbiosis-related genes, REDUCED ARBUSCULAR MYCORRHIZA1 (RAM1), REDUCED FOR ARBUSCULE DEVELOPMENT1 (RAD1), Vpy, PHOSPHATE TRANSPORTER4 (PT4), AMTs, STR, and STR2, conserved in the tested plants were transcriptionally promoted upon AM fungal colonization (Figure 3)
Summary
More than 70% of terrestrial plants associate with the symbiotic, arbuscular mycorrhizal (AM) fungi that belong to Glomeromycotina (Brundrett and Tedersoo, 2018). AM fungi supply minerals, such as inorganic phosphate and nitrogen, to their host plants, promoting the growth of the hosts (Ezawa and Saito, 2018; Wang et al, 2020). They obtain carbohydrates, such as fatty acids, lipids, and monosaccharides, from the host plants (Bravo et al, 2017; An et al, 2019). This mutual interaction is established through several steps. Some transporters are localized on a specialized plantderived membrane, periarbuscular membrane (PAM), to influx mineral nutrients and efflux carbohydrates such as lipids and glucose between the host and fungal symbionts (Kobae and Hata, 2010; Bravo et al, 2017; Luginbuehl and Oldroyd, 2017)
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