Serotonin accumulation in transgenic rice by over-expressing tryptophan decarboxylase results in a dark brown phenotype and stunted growth.
A mutant M47286 with a stunted growth, low fertility and dark-brown phenotype was identified from a T-DNA-tagged rice mutant library. This mutant contained a copy of the T-DNA tag inserted at the location where the expression of two putative tryptophan decarboxylase genes, TDC-1 and TDC-3, were activated. Enzymatic assays of both recombinant proteins showed tryptophan decarboxylase activities that converted tryptophan to tryptamine, which could be converted to serotonin by a constitutively expressed tryptamine 5' hydroxylase (T5H) in rice plants. Over-expression of TDC-1 and TDC-3 in transgenic rice recapitulated the stunted growth, darkbrown phenotype and resulted in a low fertility similar to M47286. The degree of stunted growth and dark-brown color was proportional to the expression levels of TDC-1 and TDC-3. The levels of tryptamine and serotonin accumulation in these transgenic rice lines were also directly correlated with the expression levels of TDC-1 and TDC-3. A mass spectrometry assay demonstrated that the darkbrown leaves and hulls in the TDC-overexpressing transgenic rice were caused by the accumulation of serotonin dimer and that the stunted growth and low fertility were also caused by the accumulation of serotonin and serotonin dimer, but not tryptamine. These results represent the first evidence that over-expression of TDC results in stunted growth, low fertility and the accumulation of serotonin, which when converted to serotonin dimer, leads to a dark brown plant color.
Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan.
Parawee
P
Kanjanaphachoat
Bi-Yin
BY
Wei
Shuen-Fang
SF
Lo
I-Wen
IW
Wang
Chang-Sheng
CS
Wang
Su-May
SM
Yu
Ming-Liang
ML
Yen
Sheng-Hsien
SH
Chiu
Chien-Chen
CC
Lai
Liang-Jwu
LJ
Chen
D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D019281:Dimerization; D015870:Gene Expression; D017343:Genes, Plant; D009154:Mutation; D012275:Oryza / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D010641:Phenotype; D055668:Photochemical Processes; D010858:Pigmentation / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012701:Serotonin / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D014363:Tryptamines / Q000378:metabolism; D014466:Ultraviolet Rays
D004269:DNA, Bacterial; D010940:Plant Proteins; D011994:Recombinant Proteins; C036483:T-DNA; D014363:Tryptamines; D012701:Serotonin; C030820:tryptamine; D001142:Aromatic-L-Amino-Acid Decarboxylases