The plant leucine-rich repeat receptor kinases GSO1/SGN3 and its peptide ligands CIF1 and CIF2 are essential for the formation of the Casparian strip. The Hothorn group from the Department of Botany and Plant Biology, in collaboration with the Geldner group from UNIL, has now uncovered in molecular detail how the SCHENGEN 3 receptor complex tightly binds CIF1 and CIF2.
Crystal structure of the GSO1/SGN3–CIF complex reveals a binding pocket for sulfotyrosine and extended back-bone interactions with CIF2. Structure-guided sequence analysis allowed to uncover previously uncharacterized CIF peptides conserved among higher plants. Quantitative binding assays with known and novel CIFs suggest that the homologous LRR-RKs GSO1/SGN3 and GSO2 have evolved unique peptide binding properties to control different developmental processes. A quantitative biochemical interaction screen, a CIF peptide antagonist and genetic analyses together implicate SERK proteins as essential coreceptor kinases required for GSO1/SGN3 and GSO2 receptor activation.
This work provides a mechanistic framework for the recognition of sequence-divergent peptide hormones in plants and was published in PNAS on January 21, 2020.