Auxin and ETTIN in Arabidopsis gynoecium morphogenesis

The phytohormone auxin has wide-ranging effects on growth and development. Genetic and physiological approaches implicate auxin flux in determination of floral organ number and patterning. This study uses a novel technique of transiently applying a polar auxin transport inhibitor, N-1-naphthylphthal amic acid (NPA), to developing Arabidopsis flowers to further characterize the role of auxin in organogenesis. NPA has marked effects on floral organ number as well as on regional specification in wild-type gynoecia, as defin ed by morphological and histological landmarks for regional boundaries, as well as tissue-specific reporter lines. NPA's effects on gynoecium patterni ng mimic the phenotype of mutations in ETTIN, a member of the auxin respons e factor family of transcription factors. In addition, application of diffe rent concentrations of NPA reveal an increased sensitivity of weak ettin al leles to disruptions in polar auxin transport. In contrast, the defects fou nd in spatula gynoecia are partially rescued by treatment with NPA. A model is proposed suggesting an apical-basal gradient of auxin during gynoecium development. This model provides a mechanism linking ETTIN's putative trans criptional regulation of auxin-responsive genes to the establishment or ela boration of tissue patterning during gynoecial development.