{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,15]],"date-time":"2026-09-15T06:04:56Z","timestamp":1789452296896,"version":"build-2803163510"},"reference-count":32,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,9,15]],"date-time":"2026-09-15T00:00:00Z","timestamp":1789430400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Plant Sci."],"abstract":"<jats:sec>\n                    <jats:title>Introduction<\/jats:title>\n                    <jats:p>Serotonin and melatonin are plant signaling molecules involved in growth, stress responses, and redox balance. While animals produce serotonin via 5\u2011hydroxytryptophan (5\u2011HTP), plants are thought to use the tryptamine pathway. Although 5\u2011HTP exists in plants, its conversion to serotonin lacks a genetically defined enzyme.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>We performed phylogenetic and structural analyses of Arabidopsis aromatic aldehyde synthase (AtAAS), expressed recombinant AtAAS, and examined its 5-HTP decarboxylase activity in vitro. Enzyme kinetic parameters were determined, and endogenous 5-HTP levels in Arabidopsis were quantified. A T-DNA insertion mutant of AtAAS was further used to assess serotonin accumulation following 5-HTP feeding and to determine endogenous levels of serotonin, N-acetylserotonin, and melatonin under normal growth conditions.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>AtAAS showed phylogenetic and structural similarities to animal aromatic amino acid decarboxylases and efficiently converted 5-HTP to serotonin in vitro (optimal pH 7.5, 55\u00b0C; Km = 1.806 mM, Vmax = 3.089 nmol\/min\/mg). Endogenous 5-HTP was detectable in Arabidopsis. Compared with wild-type plants, the AtAAS T-DNA insertion mutant exhibited reduced serotonin accumulation following 5-HTP feeding and decreased endogenous levels of downstream N-acetylserotonin and melatonin under normal growth conditions.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Discussion<\/jats:title>\n                    <jats:p>his discovery unveils enzymatic plasticity in plant serotonin biosynthesis and provides evidence for a previously unrecognized 5-HTP-dependent route in Arabidopsis.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fpls.2026.1961230","type":"journal-article","created":{"date-parts":[[2026,9,15]],"date-time":"2026-09-15T05:33:13Z","timestamp":1789450393000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Functional characterization of AtAAS as a 5-hydroxytryptophan decarboxylase linking serotonin formation to melatonin metabolism in Arabidopsis thaliana"],"prefix":"10.3389","volume":"17","author":[{"given":"Xiaohao","family":"Guo","sequence":"first","affiliation":[{"name":"National Key Laboratory of Rice Breeding and Biology, and Zhejiang Provincial Key Laboratory of Crop Germplasm Innovation and Exploitation, The Advanced Seed Institute, Zhejiang University","place":["Hangzhou, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Siyu","family":"Lin","sequence":"additional","affiliation":[{"name":"National Key Laboratory of Rice Breeding and Biology, and Zhejiang Provincial Key Laboratory of Crop Germplasm Innovation and Exploitation, The Advanced Seed Institute, Zhejiang University","place":["Hangzhou, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chuan","family":"Dong","sequence":"additional","affiliation":[{"name":"State Key Laboratory for Development and Utilization of Forest Food Resources, Zhejiang A&F University","place":["Hangzhou, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xinyu","family":"Huang","sequence":"additional","affiliation":[{"name":"National Key Laboratory of Rice Breeding and Biology, and Zhejiang Provincial Key Laboratory of Crop Germplasm Innovation and Exploitation, The Advanced Seed Institute, Zhejiang University","place":["Hangzhou, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hailian","family":"Hu","sequence":"additional","affiliation":[{"name":"School of Marine Biology, Xiamen Ocean Vocational College, Applied Technology Engineering Center of Fujian Provincial Higher Education for Marine Resource Protection and Ecological Governance, Xiamen Key Laboratory of Intelligent Fishery","place":["Xiamen, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Baohai","family":"Li","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Soil Pollution Control and Safety, Zhejiang University","place":["Hangzhou, China"]},{"name":"Ministry of Education (MOE) Key Laboratory of Environment Remediation and Ecological Health, College of Environmental and Resource Sciences, Zhejiang University","place":["Hangzhou, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuanyuan","family":"Tan","sequence":"additional","affiliation":[{"name":"National Key Laboratory of Rice Breeding and Biology, and Zhejiang Provincial Key Laboratory of Crop Germplasm Innovation and Exploitation, The Advanced Seed Institute, Zhejiang University","place":["Hangzhou, China"]},{"name":"Zhejiang University - Wuxi Xishan Joint Modern Agricultural Research Centre, Zhejiang University","place":["Hangzhou, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qingyao","family":"Shu","sequence":"additional","affiliation":[{"name":"National Key Laboratory of Rice Breeding and Biology, and Zhejiang Provincial Key Laboratory of Crop Germplasm Innovation and Exploitation, The Advanced Seed Institute, Zhejiang University","place":["Hangzhou, China"]},{"name":"Zhejiang University - Wuxi Xishan Joint Modern Agricultural Research Centre, Zhejiang University","place":["Hangzhou, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,9,15]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","DOI":"10.1080\/15592324.2026.2627686","article-title":"Exploring the role of serotonin as a plant stress modulator","volume":"21","author":"Amiri","year":"2026","journal-title":"Plant Signaling Behav."},{"key":"B2","doi-asserted-by":"publisher","first-page":"376","DOI":"10.1111\/tpj.14915","article-title":"Melatonin metabolism, signaling and possible roles in plants","volume":"105","author":"Back","year":"2021","journal-title":"Plant J."},{"key":"B3","doi-asserted-by":"publisher","first-page":"529","DOI":"10.1038\/210529a0","article-title":"Occurrence of 5-hydroxy-L-tryptophan as a free plant amino-acid","volume":"210","author":"Bell","year":"1966","journal-title":"Nature"},{"key":"B4","doi-asserted-by":"publisher","first-page":"219","DOI":"10.1111\/jpi.12160","article-title":"Caffeic acid O\u2010methyltransferase is involved in the synthesis of melatonin by methylating N\u2010acetylserotonin in Arabidopsis","volume":"57","author":"Byeon","year":"2014","journal-title":"J. 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