ORCID Profile
0000-0002-0588-8075
Current Organisation
Kyushu University
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Publisher: Cold Spring Harbor Laboratory
Date: 03-09-2019
DOI: 10.1101/754937
Abstract: Karrikins (KARs), smoke-derived butenolides, are perceived by the α/β-fold hydrolase KARRIKIN INSENSITIVE2 (KAI2) and are thought to mimic endogenous, yet elusive plant hormones tentatively called KAI2-ligands (KLs). The sensitivity to different karrikin types as well as the number of KAI2 paralogs varies among plant species, suggesting ersification and co-evolution of ligand-receptor relationships. In legumes, which comprise a number of important crops with protein-rich, nutritious seed, KAI2 has duplicated. We report sub-functionalization of KAI2a and KAI2b in the model legume Lotus japonicus and demonstrate that their ability to bind the synthetic ligand GR24 ent -5DS differs in vitro as well as in genetic assays in Lotus japonicus and in the heterologous Arabidopsis thaliana background. These differences can be explained by the exchange of a widely conserved phenylalanine in the binding pocket of KAI2a with a tryptophan in KAI2b, which occured independently in KAI2 proteins of several unrelated angiosperms. Furthermore, two polymorphic residues in the binding pocket are conserved across a number of legumes and may contribute to ligand binding preferences. Unexpectedly, L. japonicus responds to erse synthetic KAI2-ligands in an organ-specific manner. Hypocotyl development responds to KAR 1 , KAR 2 and rac -GR24, while root system development responds only to KAR 1 . This organ-specificity cannot be explained by receptor-ligand preferences alone, because Lj KAI2a is sufficient for karrikin responses in the hypocotyl, while Lj KAI2a and Lj KAI2b operate redundantly in roots. Our findings open novel research avenues into the evolution and ersity of butenolide ligand-receptor relationships, their ecological significance and the mechanisms controlling erse developmental responses to different KAI2 ligands.
Publisher: Public Library of Science (PLoS)
Date: 28-12-2020
DOI: 10.1371/JOURNAL.PGEN.1009249
Abstract: Karrikins (KARs), smoke-derived butenolides, are perceived by the α/β-fold hydrolase KARRIKIN INSENSITIVE2 (KAI2) and thought to mimic endogenous, yet elusive plant hormones tentatively called KAI2-ligands (KLs). The sensitivity to different karrikin types as well as the number of KAI2 paralogs varies among plant species, suggesting ersification and co-evolution of ligand-receptor relationships. We found that the genomes of legumes, comprising a number of important crops with protein-rich, nutritious seed, contain two or more KAI2 copies. We uncover sub-functionalization of the two KAI2 versions in the model legume Lotus japonicus and demonstrate differences in their ability to bind the synthetic ligand GR24 ent -5DS in vitro and in genetic assays with Lotus japonicus and the heterologous Arabidopsis thaliana background. These differences can be explained by the exchange of a widely conserved phenylalanine in the binding pocket of KAI2a with a tryptophan in KAI2b, which arose independently in KAI2 proteins of several unrelated angiosperms. Furthermore, two polymorphic residues in the binding pocket are conserved across a number of legumes and may contribute to ligand binding preferences. The ersification of KAI2 binding pockets suggests the occurrence of several different KLs acting in non-fire following plants, or an escape from possible antagonistic exogenous molecules. Unexpectedly, L . japonicus responds to erse synthetic KAI2-ligands in an organ-specific manner. Hypocotyl growth responds to KAR 1 , KAR 2 and rac -GR24, while root system development responds only to KAR 1 . This differential responsiveness cannot be explained by receptor-ligand preferences alone, because Lj KAI2a is sufficient for karrikin responses in the hypocotyl, while Lj KAI2a and Lj KAI2b operate redundantly in roots. Instead, it likely reflects differences between plant organs in their ability to transport or metabolise the synthetic KLs. Our findings provide new insights into the evolution and ersity of butenolide ligand-receptor relationships, and open novel research avenues into their ecological significance and the mechanisms controlling developmental responses to ergent KLs.
No related grants have been discovered for Mitsuru Shindo.