Auxin and tryptophan homeostasis are facilitated by the ISS1/VAS1 aromatic aminotransferase in arabidopsis
Files
Published version
Date
2015-09
Authors
Pieck, Michael
Yuan, Youxi
Godfrey, Jason
Fisher, Christopher
Zolj, Sanda
Vaughan, Dylan
Thomas, Nicholas
Wu, Connie
Ramos, Julian
Lee, Norman
Version
OA Version
Citation
Michael Pieck, Youxi Yuan, Jason Godfrey, Christopher Fisher, Sanda Zolj, Dylan Vaughan, Nicholas Thomas, Connie Wu, Julian Ramos, Norman Lee, Jennifer Normanly, John L Celenza. 2015. "Auxin and Tryptophan Homeostasis Are Facilitated by the ISS1/VAS1 Aromatic Aminotransferase in Arabidopsis.." Genetics, Volume 201, Issue 1, pp. 185 - 199.
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.