S cysteine‐rich (SCR) binding domain analysis of the Brassica self‐incompatibility S‐locus receptor kinase
2007
Kemp, Benjamin P. | Doughty, James
• Brassica self‐incompatibility, a highly discriminating outbreeding mechanism, has become a paradigm for the study of plant cell–cell communications. When self‐pollen lands on a stigma, the male ligand S cysteine‐rich (SCR), which is present in the pollen coat, is transmitted to the female receptor, S‐locus receptor kinase (SRK). SRK is a membrane‐spanning serine/threonine receptor kinase present in the stigmatic papillar cell membrane. Haplotype‐specific binding of SCR to SRK brings about pollen rejection. • The extracellular receptor domain of SRK (eSRK) is responsible for binding SCR. Based on sequence homology, eSRK can be divided into three subdomains: B lectin‐like, hypervariable, and PAN. • Biochemical analysis of these subdomains showed that the hypervariable subdomain is responsible for most of the SCR binding capacity of eSRK, whereas the B lectin‐like and PAN domains have little, if any, affinity for SCR. Fine mapping of the SCR binding region of SRK using a peptide array revealed a region of the hypervariable subdomain that plays a key role in binding the SCR molecule. • We show that residues within the hypervariable subdomain define SRK binding and are likely to be involved in defining haplotype specificity.
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