Differential Gene Expression in Rhododendron fortunei Roots Colonized by an Ericoid Mycorrhizal Fungus and Increased Nitrogen Absorption and Plant Growth

Abstract

Ericoid mycorrhizal (ERM) fungi are specifically symbiotic with plants in the family Ericaceae. Little is known thus far about their symbiotic establishment and subsequent nitrogen (N) uptake at the molecular level. The present study devised a system for establishing a symbiotic relationship between Rhododendron fortunei Lindl. and an ERM fungus (Oidiodendron maius var. maius strain Om19), quantified seedling growth and N uptake, and compared transcriptome profiling between colonized and uncolonized roots using RNA-Seq. The Om19 colonization induced 16,892 genes that were differentially expressed in plant roots, of which 14,364 were upregulated and 2,528 were downregulated. These genes included those homologous to ATP-binding cassette transporters, calcium/calmodulin-dependent kinases, and symbiosis receptor-like kinases. N metabolism was particularly active in Om19-colonized roots, and 51 genes were upregulated, such as nitrate transporters, nitrate reductase, nitrite reductase, ammonium transporters, glutamine synthetase, and glutamate synthase. Transcriptome analysis also identified a series of genes involving endocytosis, Fc-gamma R-mediated phagocytosis, glycerophospholipid metabolism, and Gonadotropin-releasing hormone (GnRH) signal pathway that have not been reported previously. Their roles in the symbiosis require further investigation. The Om19 colonization significantly increased N uptake and seedling growth. Total N content and dry weight of colonized seedlings were 36.6 and 46.6% greater than control seedlings. This is the first transcriptome analysis of a species from the family Ericaceae colonized by an ERM fungus. The findings from this study will shed light on the mechanisms underlying symbiotic relationships of ericaceous species with ERM fungi and the symbiosis-resultant N uptake and plant growth.

Ericoid mycorrhizal fungus enhances microcutting rooting of Rhododendron fortunei and subsequent growth

“…The increased expression of NRT-1, AMT2, and PHT suggested that plants effectively absorbed NO 3 − , NH 4 + , and P (Table 1). Similar to AM fungi, mycelium of Om19 took up NO 3 − , which was converted to arginine; through the action of arginase and urease, ammonium was released from arginine to plant roots 37 . The elevated ammonium in plants could induce GS and GOGAT activities.…”

“…A recent report showed that inoculation of ErM fungi significantly increased root and shoot biomass of bilberry 36 . Our previous study showed that seedlings of R. fortunei inoculated with an ErM fungus (O. maius strain Om19) produced abundant roots 37,38 . Furthermore, we observed that some senesced leaves after dropping from in vitro cultured R. fortunei onto a peat-based substrate inoculated with Om19 were able to produce ARs, but no ARs appeared in the fallen leaves on the same substrate devoid of Om19.…”

Controlled-Release Fertilizers as a Means to Reduce Nitrogen Leaching and Runoff in Container-Grown Plant Production

“…Polymer-clay superabsorbent composites have been reported to be promising as their production costs are low with high water absorbency [75]. Additionally, future CRFs should consider the incorporation of beneficial microbes, such as plant growth promoting bacteria [76] and mycorrhizal fungi [77,78] to maximize nutrient use efficiency and minimize negative impact on the environment.…”

Different Nitrate and Ammonium Ratios Affect Growth and Physiological Characteristics of Camellia oleifera Abel. Seedlings

“…(5) Root-associated microbes could be another factor influencing N uptake, such as mycorrhizal fungi [37]. Roots of Rhododendron fortunei Lindl., also an acid-loving plant, can effectively use NO 3 − due to the presence of ericoid mycorrhizal fungus (Oidiodendron maius) that can fully utilize NO 3 − [38,39]. It is unknown if C. sinensis and C. oleiferea have different rhizosphere mycorrhizal fungi or other microbes.…”