Lotus japonicus symRK-14 uncouples the cortical and epidermal symbiotic program

Area of Science:

• Plant biology
• Molecular genetics
• Symbiosis research

Background:

• SYMRK (leucine-rich-repeat receptor kinase) is crucial for legume symbiosis with rhizobia and mycorrhizal fungi.
• It mediates epidermal calcium spiking, essential for intracellular accommodation and nodule organogenesis.

Purpose of the Study:

• To investigate the function of a conserved GDPC amino acid sequence in the SYMRK extracellular domain.
• To analyze the effects of the symRK-14 mutation on symbiotic signaling pathways in Lotus japonicus.

Main Methods:

• Characterization of the symRK-14 mutant in Lotus japonicus.
• Analysis of epidermal infection by fungal and bacterial symbionts.
• Assessment of calcium spiking, NIN gene expression, and infection thread formation.
• Evaluation of nodule primordia and cortical infection development.

Main Results:

• The symRK-14 mutation aborted epidermal infection by symbionts.
• Epidermal symbiotic responses, including calcium spiking and NIN expression, were significantly reduced.
• Nodule primordia and cortical infection were largely unaffected, indicating a split symbiotic program.

Conclusions:

• The SYMRK extracellular domain's GDPC sequence is vital for transducing distinct signaling events in plant symbiosis.
• The symRK-14 mutation uncouples the epidermal and cortical symbiotic pathways.
• The conserved GDPC sequence may have non-symbiotic roles in other plant species.