Auxin synthesized by the YUCCA flavin monooxygenases is essential for embryogenesis and leaf formation in Arabidopsis.

Auxin plays a key role in embryogenesis and seedling development, but the auxin sources for the two processes are not defined. Here, we demonstrate that auxin synthesized by the YUCCA (YUC) flavin monooxygenases is essential for the establishment of the basal body region during embryogenesis and the formation of embryonic and postembryonic organs. Both YUC1 and YUC4 are expressed in discrete groups of cells throughout embryogenesis, and their expression patterns overlap with those of YUC10 and YUC11 during embryogenesis. The quadruple mutants of yuc1 yuc4 yuc10 yuc11 fail to develop a hypocotyl and a root meristem, a phenotype similar to those of mp and tir1 afb1 afb2 afb3 auxin signaling mutants. We further show that YUC genes play an essential role in the formation of rosette leaves by analyzing combinations of yuc mutants and the polar auxin transport mutants pin1 and aux1. Disruption of YUC1, YUC4, or PIN1 alone does not abolish leaf formation, but the triple mutant yuc1 yuc4 pin1 fails to form leaves and flowers. Furthermore, disruption of auxin influx carrier AUX1 in the quadruple mutant yuc1 yuc2 yuc4 yuc6, but not in wild-type background, phenocopies yuc1 yuc4 pin1, demonstrating that auxin influx is required for plant leaf and flower development. Our data demonstrate that auxin synthesized by the YUC flavin monooxygenases is an essential auxin source for Arabidopsis thaliana embryogenesis and postembryonic organ formation.