Structural modules for receptor dimerization in the S-locus receptor kinase extracellular domain

Area of Science:

• Plant reproductive biology
• Molecular genetics
• Biochemistry

Background:

• The S-locus receptor kinase (SRK) is crucial for self-incompatibility in Brassicaceae.
• SRK mediates pollen recognition via its extracellular region (eSRK) binding to S-locus cysteine-rich (SCR) ligands.
• Receptor kinases, including SRK, can dimerize even without ligand binding.

Purpose of the Study:

• To identify domains within eSRK responsible for ligand-independent dimerization.
• To investigate the role of SRK polymorphism in dimerization specificity.
• To understand the molecular basis of SRK codominance and dominance/recessiveness in self-incompatibility.

Main Methods:

• Yeast two-hybrid assays to detect eSRK self-interaction.
• Homology modeling and fold recognition techniques to infer protein structures.
• Analysis of eSRK variants to assess dimerization preferences.

Main Results:

• SRK dimerization is mediated by two regions in eSRK: a PAN_APPLE-like domain and an S-domain/EGF-like region.
• eSRK shows a strong preference for homodimerization over heterodimerization.
• A highly variable region within the PAN_APPLE domain mediates this homodimerization preference.
• eSRK polymorphism affects both SCR ligand binding and SRK dimerization specificity.

Conclusions:

• SRK homodimerization preference, driven by polymorphic regions, explains codominance in heterozygous stigmas.
• Altered heterodimerization propensities and reduced affinities may underlie dominant-recessive or mutual weakening interactions between SRK alleles.