For countless millennia, an intricate underground tango has been unfolding out of sight. In a mysterious molecular dance, plants and soil-dwelling arbuscular mycorrhizal (AM) fungi have forged an unlikely partnership, together navigating the delicate walk of symbiotic exchange.
Recent breakthroughs illuminated by scientists at the Boyce Thompson Institute (BTI) have begun unveiling the secrets behind this enigmatic, but vital, ecological dance. Their research published in Science sheds new light on the key proteins and pathways governing the biological ballet between plants and their fungal partners.
An Overview of Plant-Fungal Symbiosis: An Intimate Cellular Pas de Deux
Plant-fungal symbiosis refers to the intimate relationship formed between plants and AM fungi residing within their root cells. The plant supplies the fungus with sugars and lipids. In return, the fungus provides the plant with water, nutrients like phosphate, and protection against pathogens.
This complex, co-dependent exchange dates back roughly 450 million years. Today the partnership is essential for both organisms’ survival and shapes ecosystems the world over. However, many mysteries still surround the molecular signals allowing plants and fungi to recognize one another, establish bonds, and initiate symbiotic structures.
Advances in biotechnology recently enabled scientists to elucidate some of these secrets, unmasking new dimensions of nature’s complexity hidden below.
CKL Proteins Take Center Stage, Directing the Lipid Flow
A research team led by Dr. Maria Harrison at BTI identified two essential proteins, CKL1 and CKL2, found specifically in plant root cells harboring AM fungi. These cellulose synthase-like (CSL) proteins belong to the CKL protein family, but interestingly aren’t involved in cellulose production like other CSLs.
Rather, the CKLs display adaptations enabling association with cell membranes. There, they act akin to choreographers, directing the flow of lipids from plants to their fungal partners. This movement of fats, oils and other lipids serves as a vital source of nutrition for the AM fungi nestled inside root cells.
The Supporting Cast: Receptor Kinases Coordinate Key Signals
The lipid flow overseen by lead dancers CKL1 and CKL2 doesn’t happen in isolation. Additional research revealed supporting receptor kinase proteins that partner with CKLs and transmit important signals for this process.
These membrane-bound receptor kinase proteins have a dual role to play. First, certain kinases facilitate early recognition and penetration of AM fungal hyphae into root cells. Later, they interact with CKLs to switch on production of symbiosis-specific lipids destined for the fungal symbiont.
Following the Molecular Signals Down the Lipid Symbiosis Pathway
When CKL proteins and receptor kinases come together, they act as master regulators triggering lipid transfer down a symbiotic pathway involving other key players like RAM1 and RAM2.
CKLs control activation of RAM1-dependent genes needed to initiate the pathway. Additionally, they ensure genes required further downstream for lipid export don’t get switched on until the fungal partner is ready to receive them. This prevents wasted energy by the plant.
Ultimately RAM1 and RAM2 work together to stimulate lipid biosynthesis and assembly of lipid transport machinery at the plant-fungus interface. Yet keeping this pathway in check is also important, as rampant fungal growth could otherwise overwhelm the plant cell.
The Broader Implications of the Molecular Dance for Agriculture
Illuminating the molecular signals underlying plant-fungus symbiotic relationships holds exciting implications for the future. As lead researcher Dr. Maria Harrison explains, “Learning how plants interact with beneficial fungi at the molecular level is helping us understand how we may be able to enhance these associations in crops.”
Leveraging plant-fungal symbiosis could enable more efficient nutrient capture, drought resilience, and disease resistance in important agricultural crops like soybean, rice, and potato. With environmental stressors like climate change threatening crop yields, unlocking the secrets of this intricate biological dance takes on new urgency.
Deeper Dimensions of Nature’s Hidden Complexity Revealed
By unveiling some of the secret molecular handshakes allowing plants and fungi to partner underground, this research provides deeper insight into nature’s dazzling complexity. It compels us to appreciate the seen and unseen connections sustaining life all around us.
As lead author Dr. Maria Harrison observes, “Soils host an unseen world of microscopic organisms engaging in complex biology that impacts our daily lives.” The next time we admire a towering tree or bountiful crop growing above ground, it pays to reflect upon the hidden tango enabling it all – the lively molecular dance flourishing beneath our feet.
Additional Details on Funding, Authors and Sources
Funding for this research was provided by the US National Science Foundation’s Plant Genome Research Program.
The study was authored by scientists from the Boyce Thompson Institute located in Ithaca, NY. BTI is an independent nonprofit research institute focused on using plant sciences to improve agriculture, protect the environment, and enhance human nutrition and health globally. Read more about their research at BTIscience.org.
