Regulation of IAA Metabolism in Auxin Biosynthesis Mutants in Arabidopsis

Abstract

Auxins, a group of phytohormones, regulate plant growth and development. For biosynthesis of a naturally occurring auxin, indole-3-acetic acid (IAA), Arabidopsis has four possible pathways: the YUCCA (YUC) pathway, the CYP79B pathway, the indole-3-pyruvic acid pathway and the indole-3-acetamide pathway. IAA biosynthesis-suppressed mutants such yuc quadruple knockout lines show IAA-deficient phenotype, but IAA levels are not greatly affected in these mutants at the normal growth condition. To address this question, we have analyzed the levels of IAA metabolites in Arabidopsis IAA biosynthesis mutants. We found that IAA-amino acid conjugates are significantly decreased in the CYP79B-deficient mutants. The levels of IAA-amino acid conjugates were dramatically increased in the YUC2-overexpression mutants. These results indicate that the IAA metabolic pathways may have important roles to maintain IAA levels in IAA biosynthesis-deficient mutants.