AP2-domain transcription factor WRI5a-regulated MtABCB1 promotes arbuscule development in mycorrhizal symbiosis

Arbuscular mycorrhizal (AM) symbiosis is a mutualistic interaction between soil-dwelling AM fungi and plant roots, facilitating the efficient uptake of essential nutrients such as phosphorus and nitrogen from the soil.

It is estimated that over 70% of the phosphorus in plants is supplied by AM fungi, while plants in turn allocate approximately 10%–22% of their photosynthates—mainly in the form of fatty acids—to support fungal growth.

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Through molecular signaling, AM fungi penetrate the root epidermis and form highly branched structures known as arbuscules within the cortical cells. These arbuscules are enveloped by a host-derived periarbuscular membrane, which forms the interface for nutrient exchange between the symbiotic partners.

Core discoveries

By analyzing the M. truncatula Gene Expression Atlas (MtGEA), researchers in China discovered that at least 10 ABCB family genes were specifically induced during AM symbiosis. Among them, MtABCB1 exhibited the highest induction level specifically in arbuscule-containing cells. The Mtabcb1 mutants displayed impaired arbuscule development, indicating the essential role of MtABCB1 in AM symbiosis.

Functional experiments in yeast and plant systems demonstrated that MtABCB1 possesses auxin efflux activity like its Arabidopsis orthologs AtABCB1 and AtABCB19. Based on genetic and biochemical data, we propose that MtABCB1 likely influences arbuscule development by modulating the distribution and homeostasis of auxin within symbiotic cells, thereby revealing a novel functional mechanism for auxin signaling in AM symbiosis.

Building upon the team’s previous findings on how WRI5a regulates the fatty acid-phosphorus nutrient exchange in AM symbiosis, this study further expands our understanding of the signaling regulatory network governing this widespread symbiosis. It reveals, at multiple levels, how plants coordinate hormone signaling with nutrient exchange during AM symbiosis. These research findings not only advance our understanding of plant-fungal symbiotic interactions but also provide new targets for the development of AM fungi-based biofertilizers for agriculture.