Receptor-associated kinases control the lipid provisioning program in plant–fungal symbiosis

 

Editor’s summary

Most vascular plants form symbioses in their roots with arbuscular mycorrhizal (AM) fungi. The fungi provide nutrients such as phosphate in return for lipids provided by the plant. The transcription factor RAM1 is required for AM symbioses and regulates lipid provisioning. Ivanov and Harrison found another mechanism by which plants control lipid production and transport to fungi. This system involves two cyclin-dependent kinase–like proteins that operate both in parallel and in conjunction with the established RAM1 pathway. This work gives insight into a regulatory process fundamental to plant nutrition and growth. —Madeleine Seale

Abstract

The mutualistic association between plants and arbuscular mycorrhizal (AM) fungi requires intracellular accommodation of the fungal symbiont and maintenance by means of lipid provisioning. Symbiosis signaling through lysin motif (LysM) receptor-like kinases and a leucine-rich repeat receptor-like kinase DOES NOT MAKE INFECTIONS 2 (DMI2) activates transcriptional programs that underlie fungal passage through the epidermis and accommodation in cortical cells. We show that two Medicago truncatula cortical cell–specific, membrane-bound proteins of a CYCLIN-DEPENDENT KINASE-LIKE (CKL) family associate with, and are phosphorylation substrates of, DMI2 and a subset of the LysM receptor kinases. CKL1 and CKL2 are required for AM symbiosis and control expression of transcription factors that regulate part of the lipid provisioning program. Onset of lipid provisioning is coupled with arbuscule branching and with the REDUCED ARBUSCULAR MYCORRHIZA 1 (RAM1) regulon for complete endosymbiont accommodation.

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