Minisymposium 14: Reproductive development

Abs # 27003: Expression Based Gene Discovery of Putative Regulators of Ovule Development in Arabidopsis

Presenter:	Skinner, Debra J, djskinner@ucdavis.edu
Authors	Skinner, Debra J (A) (B)  Gasser, Charles S (A)
Affiliations:	(A): University of Califonia, Davis (Molecular and Cellular Biology) (B): Genetics Graduate Group

Arabidopsis ovules are relatively simple structures comprising 4 morphologically distinct parts: a terminal nucellus, in which the embryo sac develops, two integuments that grow to become a seed coat and a funiculus that anchors the ovule within the carpel. We are using ovules as a model system to study developmental processes such as pattern formation and cell differentiation. Several important regulators of ovule morphogenesis have been identified through screens for mutants with effects on specific individual ovule parts. However, redundancy or pleiotropic effects may preclude identification of some loci using forward genetic approaches. In particular, mutant analysis has not yet allowed a good understanding of inner integument morphogenesis. In order to access genes involved in this and other processes, Affymetrix microarrays representing most of the Arabidopsis transcriptome are being used for expression-based gene discovery. The experiments are designed to identify sets of genes expressed in particular ovule parts by comparison of pistil mRNA from wild type with mRNA from mutants that lack these parts. Genes whose mRNA concentration is significantly lower in the mutant samples relative to the wild-type samples are likely to be preferentially expressed in the ovule part missing in that mutant. Two mutants with altered integument phenotypes have been investigated: the inner no outer (ino) mutant, which lacks the outer integument, and aintegumenta (ant), a mutant that lacks both integuments among other plant defects. Comparisons of expression values from pools of pistils from these mutants and from wild type have allowed identification of genes that may be required in ovule development. From the 22,810 genes represented on the chip, approximately 250 genes show significant variation among the three genotypes and different developmental stages. Cluster analysis and pairwise comparisons of this set of genes has been used to reveal different classes of expression profile during ovule development. For example, a small set of genes is present in wild type and ino pistils but absent from ant pistils, indicating that these genes may be preferentially expressed in the inner integument. One member of this set is a putative transcription factor with a known mutant phenotype of altered integument morphology. Expression verification as well as loss-of-function analyses will be described for selected genes discovered in these experiments.