RT Journal Article
SR Electronic
T1 Identification of an Arabidopsis Aminotransferase that Facilitates Tryptophan and Auxin Homeostasis
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 013821
DO 10.1101/013821
A1 Michael Pieck
A1 Youxi Yuan
A1 Jason Godfrey
A1 Christopher Fisher
A1 Sanda Zolj
A1 Nicholas Thomas
A1 Connie Wu
A1 Julian Ramos
A1 Norman Lee
A1 Jennifer Normanly
A1 John Celenza
YR 2015
UL http://biorxiv.org/content/early/2015/01/16/013821.abstract
AB 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 (Indole Severe Sensitive) 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 indolesupplemented 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.