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Doctoral thesis, 2009

SHI/STY-family members redundantly regulate auxin homeostasis in basal and higher plants

Eklund, Magnus

Abstract

The hormone auxin plays fundamental roles in plant development by stimulating growth and differentiation of cells and tissues. Auxin action appears to rely on the formation of auxin gradients and/or concentration maxima, in large created by polar auxin transport. However, recent studies suggest that auxin synthesis also commence at sites of high auxin signaling and that spatiotemporal control of auxin biosynthesis may be required in the formation or maintenance of certain auxin maxima. The SHI/STY-family member STYLISH1 (STY1) has previously been shown to induce the activity of the auxin biosynthesis gene YUCCA4 in lateral organs of Arabidopsis thaliana. This thesis describe the functional characterization of members of the embryophyte specific SHI/STY-family in the model species A. thaliana and Physcomitrella patens. Phenotypic analysis of A. thaliana plants carrying mutations in SHI/STY-family genes revealed that the gene products act highly redundant and in a dose-dependent manner in flower and leaf development. Protein studies showed that SHI/STY proteins regulate auxin biosynthesis by acting as transcriptional activators interacting with the YUC4 promoter. Additionally, promoters of other auxin biosynthesis-related genes were activated by STY1. The sequence targeted by STY1 was identified by comparing target gene promoters. Mutations in the identified element abolished STY1-YUC4 interaction in yeast. A conserved promoter element was also discovered in most SHI/STY members, including STY1. This element was shown to be essential for gene expression in most aerial organs and could be the target of AP2/ERF-family members. Identical expression patterns and knock-out mutant phenotypes of the moss P. patens SHI/STY-family members indicated that they act redundantly, as in A. thaliana. The knock-out and overexpressor lines showed phenotypes related to reduced and increased auxin levels, respectively, and the overexpressor lines indeed displayed elevated auxin levels. The SHI/STY genes of moss and higher plants are very similar and we suggest that they perform conserved functions.

Keywords

arabidopsis thaliana; bryophyta; auxins; biosynthesis; plant developmental stages; homeostasis; genes; gene expression; transcription; transcription factors

Published in

Acta Universitatis Agriculturae Sueciae
2009, number: 2009:9
ISBN: 9789186195564
Publisher: Dept. of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences

Authors' information

Swedish University of Agricultural Sciences, Department of Plant Biology

UKÄ Subject classification

Plant Biotechnology

URI (permanent link to this page)

https://res.slu.se/id/publ/22763