© 2007 The Author(s).
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RESEARCH PAPER |
Functional analysis of a RING domain ankyrin repeat protein that is highly expressed during flower senescence
1Department of Plant Sciences, University of California Davis, One Shields Avenue, Davis, CA 95616, USA
2Crops Pathology and Genetics Research Unit, USDA-ARS, One Shields Avenue, Davis, CA 95616, USA
* To whom correspondence should be addressed. E-mail: msreid{at}ucdavis.edu
A gene encoding a RING zinc finger ankyrin repeat protein (MjXB3), a putative E3 ubiquitin ligase, is highly expressed in petals of senescing four o'clock (Mirabilis jalapa) flowers, increasing >40 000-fold during the onset of visible senescence. The gene has homologues in many other species, and the Petunia homologue is strongly up-regulated in senescing Petunia corollas. Silencing the expression of this gene in Petunia, using virus-induced gene silencing, resulted in a 2 d extension in flower life. In Mirabilis, a 2 kb promoter region, 5’ upstream of the MjXB3 gene, was isolated. The promoter sequence included putative binding sites for many DNA-binding proteins, including the bZIP, Myb, homeodomain-leucine zipper (HD-Zip), MADS-box, and WRKY transcription factors. The construct containing a 1 kb promoter region immediately upstream of the MjXB3 gene drove the strongest expression of the β-glucuronidase (GUS) reporter gene in a transient expression assay. In Petunia, GUS expression under the control of this heterologous promoter fragment was specific to senescing flowers. The Mirabilis promoter GUS construct was tested in other flower species; while GUS activity in carnation petals was high during senescence, no expression was detected in three monocotyledonous flowers—daylily (Hemerocallis ‘Stella d'Oro’), daffodil (Narcissus pseudonarcissus ‘King Alfred’), and orchid (Dendrobium ‘Emma White’).
Key words: Floral senescence, Mirabilis jalapa, senescence-associated genes, transcription factor, ubiquitin ligase
Received 16 May 2007; Revised 27 July 2007 Accepted 30 July 2007
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