Auxin and Tryptophan Homeostasis Are Facilitated by the ISS1/VAS1 Aromatic Aminotransferase in Arabidopsis. Issue 1 (10th July 2015)

• Record Type: Journal Article
• Authors: Pieck, Michael; Yuan, Youxi; Godfrey, Jason; Fisher, Christopher; Zolj, Sanda; Vaughan, Dylan; Thomas, Nicholas; Wu, Connie; Ramos, Julian; Lee, Norman; Normanly, Jennifer; Celenza, John L
• Is Part Of: Genetics. Volume 201:Issue 1(2015)
• Page Start: 185
• Page End: 199
• Publication Date: 2015-07-10
• Subjects: Arabidopsis thaliana -- auxin -- ISS1/VAS1 -- phenylpropanoids -- tryptophan metabolism; Genetics -- Periodicals; 576.5
• DOI: 10.1534/genetics.115.180356
• Languages: English
• ISSNs: 0016-6731

Abstract

Abstract: Indole-3-acetic acid (IAA) plays a critical role in regulating numerous aspects of plant growth and development. While there is much genetic support for tryptophan-dependent (Trp-D) IAA synthesis pathways, there is little genetic evidence for tryptophan-independent (Trp-I) IAA synthesis pathways. Using Arabidopsis, we identified two mutant alleles of ISS1 ( I ndole S evere S ensitive ) that display indole-dependent IAA overproduction phenotypes including leaf epinasty and adventitious rooting. Stable isotope labeling showed that iss1, but not WT, uses primarily Trp-I IAA synthesis when grown on indole-supplemented medium. In contrast, both iss1 and WT use primarily Trp-D IAA synthesis when grown on unsupplemented medium. iss1 seedlings produce 8-fold higher levels of IAA when grown on indole and surprisingly have a 174-fold increase in Trp. These findings indicate that the iss1 mutant's increase in Trp-I IAA synthesis is due to a loss of Trp catabolism. ISS1 was identified as At1g80360, a predicted aromatic aminotransferase, and in vitro and in vivo analysis confirmed this activity. At1g80360 was previously shown to primarily carry out the conversion of indole-3-pyruvic acid to Trp as an IAA homeostatic mechanism in young seedlings. Our results suggest that in addition to this activity, in more mature plants ISS1 has a role in Trp catabolism and possibly in the metabolism of other aromatic amino acids. We postulate that this loss of Trp catabolism impacts the use of Trp-D and/or Trp-I IAA synthesis pathways.