title: Overexpression of Arabidopsis thaliana tryptophan synthase beta 1 (AtTSB1) in Arabidopsis and tomato confers tolerance to cadmium stress.
abstract: Tryptophan (Trp) is an essential amino acid in humans, and in plants, it plays a major role in the regulation of plant development and defence responses. However, little is known about Trp-mediated cadmium (Cd) tolerance. Gene expression analysis showed that Arabidopsis thaliana tryptophan synthase beta 1 (AtTSB1) is up-regulated in plants treated with Cd; hence, we investigated whether this gene is involved in Cd tolerance. Exogenous application of Trp to wild-type Arabidopsis enhances Cd tolerance. Cd tolerance in the Trp-overproducing mutant trp5-1 was associated with high chlorophyll levels and low lipid peroxidation, as indicated by malondialdehyde 4-hydroxyalkenal level, whereas the wild-type developed symptoms of severe chlorosis. Moreover, the Trp-auxotroph mutant trp2-1 was sensitive to Cd. CaMV 35S promoter-driven AtTSB1 enhanced Trp accumulation and improved Cd tolerance in transgenic Arabidopsis and tomato plants without increasing the level of Cd. Moreover, reverse transcription-polymerase chain reaction confirmed that enhanced level of Trp in AtTSB1 transgenic Arabidopsis plants affected the expression of AtZIP4 and AtZIP9 metal transporters, which interfered with Cd ion trafficking, a mechanism of transcriptional regulation that does not exist in wild-type plants. Overexpression of AtTSB1 in transgenic tomato also produced higher Trp synthase-beta enzyme activity than that in wild-type plants. These results implicate that Trp could be involved in Cd defence.
authors.affiliation: Agricultural Biotechnology Research Center, Academia Sinica, Taiwan.
authors.lastname: Sanjaya
authors.forename: Pao-Yuan
authors.initials: PY
authors.lastname: Hsiao
authors.forename: Ruey-Chih
authors.initials: RC
authors.lastname: Su
authors.forename: Swee-Suak
authors.initials: SS
authors.lastname: Ko
authors.forename: Chii-Gong
authors.initials: CG
authors.lastname: Tong
authors.forename: Ray-Yu
authors.initials: RY
authors.lastname: Yang
authors.forename: Ming-Tsair
authors.initials: MT
authors.lastname: Chan
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D017360:Arabidopsis / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002104:Cadmium / Q000633:toxicity*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D018551:Solanum lycopersicum / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism; D014367:Tryptophan Synthase / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; D002104:Cadmium; D014364:Tryptophan; D014367:Tryptophan Synthase