Cloning and Biochemical Characterization of ToFZY, a Tomato Gene Encoding a Flavin Monooxygenase Involved in a Tryptophan-dependent Auxin Biosynthesis Pathway

Indole-3-acetic acid (IAA), the main endogenous auxin, has been known for decades to be a key regulator for plant growth and development. Multiple routes have been proposed for IAA biosynthesis but physiologic roles or relevance of the different routes are still unclear. Recently, four members of the Arabidopsis thaliana YUC gene family have been implicated in an additional requirement of IAA involved in floral organ and vascular tissue formation. The loss-of-function yuc1yuc4 double mutants in Arabidopsis displayed phenotypes similar to the previously described loss-of-function floozy mutants in petunia (fzy). Moreover, it has been demonstrated that YUC1 encodes a flavin monooxygenase (FMO) that catalyzes a rate-limiting step of a tryptophan-dependent auxin biosynthesis pathway: the conversion of tryptamine to N-hydroxyl-tryptamine. Here we report on the genetic study of ToFZY, the putative tomato ortholog of YUC4 and FZY, including gene and cDNA sequence comparison and a preliminary expression analysis. In addition, we describe a novel conserved amino acid motif that may be considered a hallmark potentially useful for the identification of new YUC-like FMOs. We also demonstrate that ToFZY encodes a protein with the same enzymatic activity as YUC1. Finally, we provide evidence suggesting that the ToFZY gene belongs to a multigenic family whose members may exhibit a temporal and spatial specialization similar to that described in A. thaliana.