Biosynthesis of the Halogenated Auxin, 4-Chloroindole-3-Acetic Acid

We show that in pea seeds, 4-chloroindole-3-acetic acid is synthesized via the novel intermediate 4-chloroindole-3-pyruvic acid, which is produced from 4-chlorotryptophan by two aminotransferases, TRYPTOPHAN AMINOTRANSFERASE RELATED1 and TRYPTOPHAN AMINOTRANSFERASE RELATED2

Nathan D. Tivendale; Sandra E. Davidson; Noel W. Davies; Jason A. Smith; Marion Dalmais; Abdelhafid I. Bendahmane; Laura J. Quittenden; Lily Sutton; Raj K. Bala; Christine Le Signor; Richard Thompson; James Horne; James B. Reid; John J. Ross


Scholarcy highlights

  • Seeds of several agriculturally important legumes are rich sources of the only halogenated plant hormone, 4-chloroindole-3acetic acid
  • The large reduction in 4-Cl-indole-3-acetic acid at the later stages indicates the importance of the 4-Cl-indole3-pyruvic acid pathway for 4-Cl-IAA biosynthesis in seeds. 4-Cl-Trp was identified by UPLC-MS in seed extracts, and we found that at later stages of seed development, the extracts from mutant seeds contained significantly more 4-Cl-Trp and Trp than did extracts from wild-type seeds
  • We provide evidence for the biosynthesis of 4-Cl-IAA via the 4-chlorinated version of the
  • The novel intermediate, 4-Cl-IPyA, was detected as a product of 4-Cl-Trp, and its identity was confirmed by comparison with 4-Cl-IPyA synthesized in our laboratory
  • 4-Cl-IAA and IAA were detected, but further analysis showed that this was merely due to nonenzymatic conversion from the initial products, 4-Cl-IPyA and IPyA to 4-Cl-IAA and IAA, respectively
  • The conversion of IPyA to IAA is reportedly enzymatic in Arabidopsis
  • Solutions of D- or 13C-labeled substrates in water were injected into excised immature pea seeds, which contained liquid endosperm, using a sterile syringe, as described previously, and left up to 3 h before harvesting

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