Abstract
Phytohormone auxin is involved in various growth responses including axis formation during embryogenesis, organogenesis, vascular patterning, and tropism. Although auxin was the phytohormone discovered over 100 years ago, no molecular mechanisms of its biosynthesis, an essential aspect of auxin homeostasis, have been fully elucidated. To reveal the action of auxin during embryogenesis, we tried to identify the site and function of auxin biosynthesis. We analyzed expression of genes involved in Tryptophan-dependent IAA biosynthesis pathways, such as CYP79B2, CYP79B3, YUCCA1, 2, 3, 4, NIT1, 2, 3, and AAO1. Expression patterns of these genes were tightly regulated temporally and spatially during embryogenesis. Especially, YUCCA expression domains were identical to predicted sites of auxin biosynthesis. To elucidate the function of YUCCA genes, we performed the phenotype analysis of yucca mutants. yucca mutants exhibited the defects of organ development. These results suggest that YUCCA genes function as the origin of polar auxin transport.
