Characterization of egg cell-expressed genes in Arabidopsis thaliana

Abstract
Flowering plants  alternate between two contrasting phases during their life cycle: a haploid gametophytic phase during which gametes are formed that fuse to form the sporophyte, and a diploid sporophytic phase during which spores are formed that develop into the gametophytes. The female gametophyte (embryo sac) is buried within the ovule, the precursor of the seed. The embryo sac contains the the two female gametes, the egg and the central cells that take part in double fertilization. The molecular basis of female gametogenesis and fertilization in plants is poorly understood. To gain insights into the genetic network controlling gamete formation, Arabidopsis lines carrying transposon insertions working as enhancer detectors or gene traps were generated. By screening these transposants for specific reporter gene expression patterns in the ovule and the female gametophyte, a set of enhancer detectors with expression patterns specific to different cell types of the ovule and the gametophyte have been identified. Among them were the egg cell-specific lines whose characterization forms the basis of this proposal. Two egg cell-specific lines have partially been analyzed before and will be characterized further: An insertion in a LAMMER kinase (Line 1) and an insertion between two predicted genes of unkown function (Line 2). The expression patterns have been confirmed by promoter-GUS studies and also by preliminary in situ hybridization analysis. One goal of the project is the completion of in situ hybridization experiments with the two candidate genes. The Ds insertion in these lines is within the intronic (Line 1) or intergenic (Line 2) region and there is no associated phenotype. With the availability of T-DNA insertions in the exons of the putatively affected genes in these lines, it is now possible to functionally test if one of these genes – when mutated - leads to a detectable phenotype affecting female gametophyte development or function.

Partner Institutions:
In India:
Prof. G.K. Suraish Kumar
Dep. Of Biotechnology Indian Institute of Technology – Madras
Chennai-600 036
India
gk@iitm.ac.in

In Switzerland:
Dr. Ueli Grossniklaus
Professor of Plant Developmental Biology
Insitute of Plant Biology
University of Zürich
Zollikerstrasse 107
CH-8008 Zürich
Switzerland
grossnik@botinst.unizh.ch