Auxin Homeostasis
The plant hormone auxin influences nearly every aspect of plant growth and development. In order to be an effective signaling molecule auxin levels are tightly regulated by biosynthesis, conjugation, catabolism, compartmentation and transport. Recently, my lab characterized the two enzymes catalyzing the major catabolic product of auxin in Arabidopsis. Single mutants show mild defects affecting auxin responses and fertility. My lab has successfully isolated double mutants which show pronounced phenotypes. The basic research projects that my lab is pursuing are the role auxin oxidases in development, the fate of oxidized auxin in the cell, the combined contributions of biosynthesis, conjugation, catabolism, compartmentation and transport to auxin homeostasis. The applied research projects are to isolate auxin homeostatic modifiers in maize and optimize maize phyllotaxy which is regulated by auxin homeostasis, since maize phyllotaxy has been shown to be important for optimal growth and seed set. This work has also produced an intellectual property disclosure and a provisional patent.
Simplified auxin biosynthesis, conjugation, and non-decarboxylation oxidation pathways. Auxin metabolic pathway via IPyA with the three major classes of catabolic products: amide-linked, ester-linked, and oxidative. Enzymes: TAA, TRYPTOPHAN AMIDOTRANSFERASE; TAR, TRYPTOPHAN AMIDOTRANSFERASE-RELATED; YUC, YUCCA; IAMT1, IAA CARBOXYLMETHYL TRANSFERASE 1; MES17, METHYL ESTERASE 17; GH3, GRETCHEN HAGEN 3; IAR3, IAA-ALANINE RESISTANT; ILR1, IAA-LEUCINE RESISTANT 1; ILL2, IAA-LEUCINE RESISTANT-LIKE 2; UGT, UDP GLUCOSE TRANSFERASES; DAO, DIOXYGENASE OF AUXIN OXIDATION. Substrates/products: IPyA, indole-3-pyruvic acid; IAA, indole-3-acetic acid; MeOH, indole-3-acetic acid methyl ester; IAA-glc, IAA-glucose, 1-O-indole-3-acetyl-β-D-glucose; IAA-AA, IAA-amino acid conjugate; R, amino acid side chain; 6-OH-IAA-AA, N-(6-hydroxyindol-3-ylacetyl)-amino acid; oxIAA-glc, 1-O-(2-oxoindol-3-ylacetyl)-β-D-glucopyranose; oxIAA-AA, oxIAA-amino acid conjugate; oxIAA, 2-oxindole-3-acetic acid; 7-OH-oxIAA, 7-hydroxy-2-oxindole-3-acetic acid; 7-OH-oxIAA-glc, 7-O-2-oxindole-3-acetic acid 7’-O-beta- D-glucopyranoside. Arrows indicate the metabolic pathway. Dashed arrows indicate that the enzymatic reaction has not been demonstrated. Colours: GH3 and amido conjugates are in blue; DAO and oxidative conjugates are in red; UGT and glucosylated conjugates are in green; IAMT and methylated ester are in pink. From Zhang and Peer, 2017, Journal of Experimental Botany