The plant tryptophan (Trp) biosynthetic pathway produces many secondary metabolites with diverse functions. Indole- 3-acetic acid (IAA), proposed as a derivative from Trp or its precursors, plays an essential role in plant growth and development. Although the Trp-dependant and Trp-independent IAA biosynthetic pathways have been proposed, the enzymes, reactions and regulatory mechanisms are largely unknown. In Arabidopsis, indole-3-glycerol phosphate (IGP) is suggested to serve as a branchpoint component in the Trp-independent IAA biosynthesis. To address whether other enzymes in addition to Trp synthase α (TSA1) catalyze IGP cleavage, we identified and characterized an indole synthase (INS) gene, a homolog of TSA1 in Arabidopsis. INS exhibits different subcellular localization from TSA1 owing to the lack of chloroplast transit peptide (cTP). In silico data show that the expression levels of INS and TSA1 in all examined organs are quite different. Histochemical staining of INS promoter-GUS transgenic lines indicates that INS is expressed in vascular tissue of cotyledons, hypocotyls, roots and rosette leaves as well as in flowers and siliques. INS is capable of complementing the Trp auxotrophy of Escherichia coli trpA strain, which is defective in Trp synthesis due to the deletion of TSA. This implies that INS catalyzes the conversion of IGP to indole and may be involved in the biosynthesis of Trp-independent IAA or other secondary metabolites in Arabidopsis.
The KNAT1 gene is a member of the Class I KNOX homeobox gene family and is thought to play an important role i...
Xiao-Qun Wang,Wei-Hui Xu,Li-Geng Ma,Zhi-Ming Fu,Xing-Wang Deng,Jia-Yang Li and Yong-Hong Wang State Key Laboratory of Plant Genomics and National Center for Plant Gene Research,Institute of Genetics and Developmental Biology,the Chinese Academy of Sciences,Beijing 100101,China Peking-Yale Joint Center of Plant Molecular Genetics and Agrobiotechnology,College of Life Sciences,Peking University,Beijing 100871,China National Institute of Biological Sciences,Zhongguancun Biological Science Park,Beijing 102206,China
