{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T01:00:10Z","timestamp":1790038810944,"version":"4.0.1"},"reference-count":57,"publisher":"National Academy of Sciences","issue":"8","license":[{"start":{"date-parts":[[2025,2,20]],"date-time":"2025-02-20T00:00:00Z","timestamp":1740009600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"JST ACT-X","award":["JPMJAX21BE"],"award-info":[{"award-number":["JPMJAX21BE"]}]}],"content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2025,2,25]]},"abstract":"<jats:p>\n                    Karrikin Insensitive 2 (KAI2), identified as the receptor protein for karrikins (KARs), which are smoke-derived seed germination stimulants, belongs to the same \u03b1\/\u03b2-hydrolase family as D14, the receptor for strigolactones (SLs). KAI2 is believed to recognize an endogenous butenolide (KAI2 ligand; KL), but the identity of this compound remains unknown. Recent studies have suggested that ligand hydrolysis by KAI2 is a prerequisite for receptor activation to induce interaction with the target proteins, similar to the situation with D14. However, direct experimental evidence has been lacking. Here, we designed KAI2 ligands (carba-dMGers) whose butenolide rings were modified so that they cannot be hydrolyzed or dissociated from the original ligand molecule by KAI2, by structurally modifying dMGer, a potent and selective KAI2 agonist. Using these dMGer analogs, we found that the strongly bioactive ligand, (+)-dMGer, was hydrolyzed by KAI2 at a lower enzymatic rate compared with the weakly bioactive ligand, (+)-1\u2032-carba-dMGer, and the hydrolyzed butenolide ring of (+)-dMGer was transiently trapped in the catalytic pocket of KAI2. Additionally, structural analysis revealed that (+)-6\u2032-carba-dMGer bound to the catalytic pocket of KAI2 in the unhydrolyzed state. However, this binding did not induce the interaction between KAI2 and SMAX1, indicating that ligand binding to the receptor alone was not sufficient for KAI2 signaling. This study showed experimental data from a ligand structure\u2013activity study that ligand hydrolysis and subsequent covalent adduct formation with the catalytic triad plays a key role in KAI2 activation, providing insight into the chemical structure of the\n                    <jats:italic>Arabidopsis<\/jats:italic>\n                    KL.\n                  <\/jats:p>","DOI":"10.1073\/pnas.2414779122","type":"journal-article","created":{"date-parts":[[2025,2,20]],"date-time":"2025-02-20T13:01:21Z","timestamp":1740056481000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":11,"title":["Structural requirements of KAI2 ligands for activation of signal transduction"],"prefix":"10.1073","volume":"122","author":[{"given":"Rito","family":"Kushihara","sequence":"first","affiliation":[{"name":"Department of Agriculture, Graduate School of Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0409-5759","authenticated-orcid":false,"given":"Akihiko","family":"Nakamura","sequence":"additional","affiliation":[{"name":"Department of Applied Life Sciences, Faculty of Agriculture, Shizuoka University","place":["Shizuoka, Japan"]},{"name":"Research Institute of Green Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]},{"name":"Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, National Institutes of Natural Sciences","place":["Okazaki, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Katsuki","family":"Takegami","sequence":"additional","affiliation":[{"name":"Department of Agriculture, Graduate School of Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1593-5717","authenticated-orcid":false,"given":"Yoshiya","family":"Seto","sequence":"additional","affiliation":[{"name":"Laboratory of Plant Chemical Regulation, Department of Agricultural Chemistry, School of Agriculture, Meiji University","place":["Kanagawa, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yusuke","family":"Kato","sequence":"additional","affiliation":[{"name":"Laboratory of Plant Chemical Regulation, Department of Agricultural Chemistry, School of Agriculture, Meiji University","place":["Kanagawa, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3919-3538","authenticated-orcid":false,"given":"Hideo","family":"Dohra","sequence":"additional","affiliation":[{"name":"Research Institute of Green Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]},{"name":"Shizuoka Instrumental Analysis Center, Shizuoka University","place":["Shizuoka, Japan"]},{"name":"Department of Biological Science, Graduate School of Integrated Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Toshiyuki","family":"Ohnishi","sequence":"additional","affiliation":[{"name":"Department of Applied Life Sciences, Faculty of Agriculture, Shizuoka University","place":["Shizuoka, Japan"]},{"name":"Research Institute of Green Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yasushi","family":"Todoroki","sequence":"additional","affiliation":[{"name":"Department of Applied Life Sciences, Faculty of Agriculture, Shizuoka University","place":["Shizuoka, Japan"]},{"name":"Research Institute of Green Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3049-8965","authenticated-orcid":false,"given":"Jun","family":"Takeuchi","sequence":"additional","affiliation":[{"name":"Department of Applied Life Sciences, Faculty of Agriculture, Shizuoka University","place":["Shizuoka, Japan"]},{"name":"Research Institute of Green Science and Technology, Shizuoka University","place":["Shizuoka, Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"341","published-online":{"date-parts":[[2025,2,20]]},"reference":[{"key":"e_1_3_4_1_2","doi-asserted-by":"publisher","DOI":"10.3389\/fpls.2014.00373"},{"key":"e_1_3_4_2_2","doi-asserted-by":"publisher","DOI":"10.1080\/09168451.2018.1462693"},{"key":"e_1_3_4_3_2","doi-asserted-by":"publisher","DOI":"10.1111\/tpj.15115"},{"key":"e_1_3_4_4_2","doi-asserted-by":"publisher","DOI":"10.1021\/acs.jafc.3c01809"},{"key":"e_1_3_4_5_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.tplants.2009.11.005"},{"key":"e_1_3_4_6_2","doi-asserted-by":"publisher","DOI":"10.1242\/dev.074567"},{"key":"e_1_3_4_7_2","doi-asserted-by":"publisher","DOI":"10.1093\/mp\/ssq055"},{"key":"e_1_3_4_8_2","doi-asserted-by":"publisher","DOI":"10.1126\/science.1099944"},{"key":"e_1_3_4_9_2","doi-asserted-by":"publisher","DOI":"10.1021\/jf9028128"},{"key":"e_1_3_4_10_2","doi-asserted-by":"publisher","DOI":"10.1104\/pp.108.131516"},{"key":"e_1_3_4_11_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.0911635107"},{"key":"e_1_3_4_12_2","doi-asserted-by":"publisher","DOI":"10.3390\/plants9010043"},{"key":"e_1_3_4_13_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.2006111117"},{"key":"e_1_3_4_14_2","doi-asserted-by":"publisher","DOI":"10.3389\/fpls.2015.01219"},{"key":"e_1_3_4_15_2","doi-asserted-by":"publisher","DOI":"10.1105\/tpc.15.00146"},{"key":"e_1_3_4_16_2","doi-asserted-by":"publisher","DOI":"10.1073\/pnas.1100987108"},{"key":"e_1_3_4_17_2","doi-asserted-by":"publisher","DOI":"10.3389\/fpls.2016.01799"},{"key":"e_1_3_4_18_2","doi-asserted-by":"publisher","DOI":"10.1126\/science.adl4685"},{"key":"e_1_3_4_19_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.cub.2012.08.007"},{"key":"e_1_3_4_20_2","doi-asserted-by":"publisher","DOI":"10.1038\/nchembio.2147"},{"key":"e_1_3_4_21_2","doi-asserted-by":"publisher","DOI":"10.1038\/nature19073"},{"key":"e_1_3_4_22_2","doi-asserted-by":"publisher","DOI":"10.1038\/cr.2015.122"},{"key":"e_1_3_4_23_2","doi-asserted-by":"publisher","DOI":"10.1038\/s41586-018-0743-5"},{"key":"e_1_3_4_24_2","doi-asserted-by":"publisher","DOI":"10.1038\/nature12870"},{"key":"e_1_3_4_25_2","doi-asserted-by":"publisher","DOI":"10.1038\/nature12878"},{"key":"e_1_3_4_26_2","doi-asserted-by":"publisher","DOI":"10.1105\/tpc.15.00562"},{"key":"e_1_3_4_27_2","doi-asserted-by":"publisher","DOI":"10.1105\/tpc.15.00605"},{"key":"e_1_3_4_28_2","first-page":"1581","article-title":"SMAX1-LIKE7 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Liang, S. Ward, P. Li, T. Bennett, O. Leyser, SMAX1-LIKE7 signals from the nucleus to regulate shoot development in Arabidopsis via partially EAR motif-independent mechanisms. 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Takegamie J. Takeuchi A. Nakamura AtKAI2 apo structure. Protein Data Bank. https:\/\/www.rcsb.org\/structure\/8ZVO. Deposited 17 Jun 2024.","DOI":"10.2210\/pdb8zvo\/pdb"},{"key":"e_1_3_4_57_2","doi-asserted-by":"crossref","unstructured":"K. Takegamie R. Koosharem A. Nakamura AtKAI2 (+)-6\u2032-carba-dMGer complex. Protein Data Bank. https:\/\/www.rcsb.org\/structure\/8ZVN. 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