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KAI2 receptors, classified as plant α/β hydrolase enzymes, are capable of perceiving smoke-derived butenolide signals and endogenous, yet unidentified KAI2-ligands (KLs). While the number of functional KAI2 receptors varies among land plant species, rice has only one KAI2 gene. Rice, a significant crop and representative of grasses, relies on KAI2-mediated Arbuscular mycorrhiza (AM) symbioses to flourish in traditionally arid and nutrient-poor environments. This study presents the first crystal structure of an active rice (Oryza sativa, Os) KAI2 hydrolase receptor. Our structural and biochemical analyses uncover grass-unique pocket residues influencing ligand sensitivity and hydrolytic activity. Through structure-guided analysis, we identify a specific residue whose mutation enables the increase or decrease of ligand perception, catalytic activity, and signal transduction. Furthermore, we investigate OsKAI2-mediated signaling by examining its ability to form a complex with its binding partner, the F-box protein DWARF3 (D3) ubiquitin ligase and subsequent degradation of the target substrate OsSMAX1, demonstrating the significant role of hydrophobic interactions in the OsKAI2-D3 interface. This study provides new insights into the diverse and pivotal roles of the OsKAI2 signaling pathway in the plant kingdom, particularly in grasses.
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Structural and functional analyses explain Pea KAI2 receptor diversity and reveal stereoselective catalysis during signal perception
Abstract KAI2 proteins are plant α/β hydrolase receptors which perceive smoke-derived butenolide signals and endogenous, yet unidentified KAI2-ligands (KLs). The number of functional KAI2 receptors varies among species and KAI2 gene duplication and sub-functionalization likely plays an adaptative role by altering specificity towards different KLs. Legumes represent one of the largest families of flowering plants and contain many agronomic crops. Prior to their diversification, KAI2 underwent duplication resulting in KAI2A and KAI2B. Here we demonstrate thatPisum sativumKAI2A and KAI2B are active receptors and enzymes with divergent ligand stereoselectivity. KAI2B has a higher affinity for and hydrolyses a broader range of substrates including strigolactone-like stereoisomers. We determine the crystal structures of PsKAI2B in apo and butenolide-bound states. The biochemical, structural, and mass spectra analyses of KAI2s reveal a transient intermediate on the catalytic serine and a stable adduct on the catalytic histidine, confirming its role as a bona fide enzyme. Our work uncovers the stereoselectivity of ligand perception and catalysis by diverged KAI2 receptors and proposes adaptive sensitivity to KAR/KL and strigolactones by KAI2B.
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- PAR ID:
- 10362628
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Communications Biology
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2399-3642
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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