Os08g0140300

L-Tryptophan decarboxylase (TDC) belong to a family of aromatic L-amino acid decarboxylases and convert tryptophan to tryptamine, which could be converted to serotonin by a constitutively expressed tryptamine 5' hydroxylase (T5H). in rice plants.

Annotated Information

Function

tryptophan decarboxlyase activities that converted tryptophan to tryptamine, which could be converted to serotonin by a constitutively expressed tryptamine 5'hydroxylase (T5H) in rice plants.transgenic plants that produced TDC showed a normal phenotype and contained 25-fold and 11-fold higher serotonin in the leaves and seeds, respectively, than the wild-type plants. A recent study showed that the expression of TDC was significantly up-regulated by inoculation with B. oryzae , which caused a marked increase in serotonin production in the defense responses of rice against pathogenic infection.

1.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.The degree of stunted growth and dark-brown color was proportional to the expression levels of TDC-1. The levels of tryptamine and serotonin accu-mulation in these transgenic rice lines were also directly correlated with the expression levels of TDC-1.In the present study, we isolated a T-DNA insertion mutant M47286, which contained a copy of the T-DNA activation-tag inserted at the location where the expression of two TDC genes, TDC - 1 and TDC - 3 (accession number BAD11583, named TDC -3 in this study), were activated and over-expressed. Accordingly, we detected an elevated level of serotonin accumulation in this mutant and in the transgenic rice plants over-expressing either TDC-1 or TDC-3. Uniformly, all the TDC-overexpressing transgenic and mutant rice plants showed stunted growth and had dark-brown leaves, panicles and grains. However, this relationship between the accumulation of serotonin and the phenotypes of dark-brown color and stunted growth has not been previously reported in rice plants. These obser-vations led to the proposition that the phenotypes that appeared in mutant M47286 and in the TDC-over-expressing transgenic rice plants resulted from the accu-mulation of serotonin and/or serotonin dimer, with the effects of serotonin or its dimer resulting in stunted growth and the accumulation of the serotonin dimer resulting in brown pigmentation. In addition, extended exposure of plants to sunlight (UV) triggered the formation of covalent serotonin dimer in the plants, resulting in brown phenotypes. Moreover, the deposition of brown material at pathogen infection sites could also resulted from the accumulation of the covalent serotonin dimer.

2.TDC plays a rate-limiting role for serotonin accumulation,and serotonin was abundant in the vascular parenchyma cells, including companion cells and xylem-parenchyma cells, suggestive of its involvement in maintaining the cellular integrity of these cells for facilitating efficient nutrient recycling from senescing leaves to sink tissues during senescence.the eno rmous in duction of serotonin synth esis in sene scing rice leaves, which is charact erized by chlo rophyll loss, me mbrane lipid peroxidation, increased reactive oxygen species (ROS), and induced senescence-related genes. It further shows that the induction of serotonin accumulation is coordi-nately regulated with the induction of the entire set of Trp biosynthetic mRNAs and is proportional to the induction of TDC protein. Furthermore, the accumula-tion of serotonin is believed to play a protective role against ROS, leading to a delay in the process of senescence as demonstrated by analyses of transgenic rice plants, such as TDCoverexpression and TD CRNA interference (RNAi) lines.

Expression

1.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 decarboxlyase genes, TDC -1 and TDC - 3 , were activated. The T-DNA insertion mutant M47286 isolated from the Taiwan Rice Insertional Mutants (TRIM) T-DNA-tagged rice mutant library was found to have stunted growth, dark-brown panicles and grains and dark green leaves used to generate the TRIM library contained multiple CaMV35S enhancers adjacent to the left border, which activated promoters located near the T-DNA insertion sites. This mutant M47286 contained a copy of the T-DNA tag The T-DNA tag inserted at the location where the expression of two puta-tive tryptophan decarboxlyase genes, TDC - 1 and TDC - 3 , were activated

2.Over-expression of TDC-1 and TDC-3 in transgenic rice recapitulated the stunted growth, dark-brown phenotype and resulted in a low fertility similar to M47286. To verify the cause of stunted growth and dark-brown phenotypes in mutant M47286, full-length cDNAs of TDC-1 (1,545 bp) and TDC-3 (1,572 bp) were isolated from rice and fused downstream of the maize ubiquitin (Ubi) (Sun and promoter, generating Ubi: TDC -1 and Ubi: TDC -3 constructs for rice transformation. More than 20 independent transgenic rice lines were obtained for each construct and showed various degrees of stunted growth and dark-brown colored phenotypes. Five independent transgenic lines confirmed by Southern blot assay from each construct were selected for further investigations. The morphological characteristics of these transgenic lines were compared to those of transgenic rice carrying the pCAMBIA 1301 vector only (WT-V).

Evolution

Serotonin (5-hydroxytryptamine) is a well-known aromatic amine neurotransmitter that controls several important physiological functions such as mood, sleep and anxiety in animals and humans. Evolutionarily, serotonin existed in plants even before the appearance of animals, with the first report coming in the fruit of the cowhage (Mucuna pruriens ) plant.Similar to the multiple roles played by serotonin in animal cells, serotonin has also been sug-gested to be involved in several physiological functions in plants, such as growth regulation , seed germination, flowering, ion per-meability, adaptation to environmental changes and morphogenesis. Recently, serotonin has been reported to accumulate in rice leaves to delay senescence and at sites of infection as part of the defensive response.

Labs working on this gene

1,Department of Biotechnology, Interdisciplinary Program for Bioenergy and Biomaterials of Graduate School, Agricultural Plant Stress Research Center, Chonnam National University, Gwangju 500-757, South Korea.

2.Department of Molecular Biotechnology, Agricultural Plant Stress Research Center, Biotechnology Research Institute, Chonnam National University, Gwangju, South Korea.

3.Institute of Molecular Biology, National Chung Hsing University, Taichung 402, Taiwan.

References

1. Parawee Kanjanaphachoat;Bi-Yin Wei;Shuen-Fang Lo;I-Wen Wang;Chang-Sheng Wang;Su-May Yu;Ming-Liang Yen;Sheng-Hsien Chiu;Chien-Chen Lai;Liang-Jwu Chen

 Serotonin accumulation in transgenic rice by over-expressing tryptophan decarboxlyase results in a dark brown phenotype and stunted growth
 Plant Molecular Biology, 2012, 78(6): 525-543

2. Kiyoon Kang;Young-Soon Kim;Sangkyu Park;Kyoungwhan Back

 Senescence-Induced Serotonin Biosynthesis and Its Role in Delaying Senescence in Rice Leaves
 Plant Physiology, 2009, 150(3): 1380-1393

3. Sei Kang;Kiyoon Kang;Kyungjin Lee;Kyoungwhan Back

 Characterization of rice tryptophan decarboxylases and their direct involvement in serotonin biosynthesis in transgenic rice
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