Summary:
In the intricate relationship between vascular plants and arbuscular mycorrhizal (AM) fungi, the exchange of nutrients and lipids plays a crucial role. The established RAM1 transcription factor is known for its involvement in AM symbioses, overseeing lipid provisioning. However, Ivanov and Harrison have uncovered an additional layer of complexity in lipid production and transport control. Their discovery revolves around two cyclin-dependent kinase–like proteins (CKL1 and CKL2), which operate in parallel and collaboration with the existing RAM1 pathway. This revelation sheds light on a fundamental regulatory process crucial for plant nutrition and growth.
Abstract:
The mutualistic bond between plants and arbuscular mycorrhizal (AM) fungi hinges on the intricate interplay of intracellular accommodation and lipid provisioning. Symbiosis signaling, orchestrated by lysin motif (LysM) receptor-like kinases and the leucine-rich repeat receptor-like kinase DOES NOT MAKE INFECTIONS 2 (DMI2), activates transcriptional programs facilitating fungal passage through the epidermis and establishment in cortical cells. This study unravels the involvement of two membrane-bound proteins, CKL1 and CKL2, belonging to the CYCLIN-DEPENDENT KINASE-LIKE (CKL) family, specific to Medicago truncatula cortical cells. These proteins associate with and serve as phosphorylation substrates for DMI2 and a subset of LysM receptor kinases. CKL1 and CKL2 emerge as essential players in AM symbiosis, influencing the expression of transcription factors that regulate a segment of the lipid provisioning program. The initiation of lipid provisioning aligns with arbuscule branching and the well-known REDUCED ARBUSCULAR MYCORRHIZA 1 (RAM1) regulon, crucial for the comprehensive accommodation of the endosymbiont. This discovery expands our understanding of the intricate regulatory mechanisms governing plant–fungal symbiosis, with implications for plant nutritional dynamics and overall growth.
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