Poster: Evolution of developmental & physiological mechanisms

Abs # 822: Expression of expansin genes in bryophytes.

Presenter:	Carey, Robert E, rec17@psu.edu
Authors	Carey, Robert E (A)   Cosgrove, Daniel  (A)
Affiliations:	(A): Department of Biology, Penn State University

The cell-wall-loosening proteins known as expansins have been shown to be involved in a number of growth and development processes in plants. In Arabidopsis thaliana, expansins are expressed in a cell-specific pattern with certain genes expressed only in one tissue type (root hairs for example). To gain insight into the evolution of the tissue specific nature of the expression pattern of this gene family, I isolated two α-expansin genes from the moss Physcomitrella patens and generated gene targeting constructs which, by taking advantage of the homologous recombination exhibited by Physcomitrella, allow the elucidation of the expression pattern and inferred functionality of these ancient bryophyte expansins. This is accomplished by creating a “replacement” vector using genomic DNA sequence from the promoter of the gene of interest and the beginning of the coding sequence flanking either end of sequence containing a Beta-glucuronidase (GUS) sequence and an nptII resistance cassette. When the moss is transformed with this construct, gene conversion events will disrupt the gene sequence with the GUS and resistance cassette sequences and allow expression of GUS driven by the endogenous promoter of the expansin gene targeted. In light of the difficulty in observing phenotypic changes in single knockouts of large gene families such as expansins, this technique has the advantage of revealing simultaneous expression pattern information and thus gives the opportunity to identify subtle phenotypic changes in specific tissue types that might otherwise be missed. In the case of expansins, this technique will also help to answer the question of when the tissue specific expression pattern of expansins arose during their evolutionary history.