Poster: Evolution

Abs # 797: Arabidopsis expansins: an evolutionary approach to functional characterization.

Presenter:	Sampedro, Javier , jus16@psu.edu
Authors	Sampedro, Javier  (A)   Durachko, Daniel M (A)   Cosgrove, Daniel J (A)
Affiliations:	(A): Department of Biology / Penn State University

Arabidopsis has 36 expansin genes, two of which are disrupted in the Columbia, but not Landsberg erecta, ecotype. Syntenic regions in the genome have been interpreted as traces of three whole genome duplications. Most expansins genes are located in regions with a significant degree of synteny to other expansin-containing segments. This has allowed us to infer that all Arabidopsis expansins are descendants of at most 15 genes present in the Arabidopsis ancestor before the first detectable round of genome duplication. The three rounds created 11 new expansin genes whose ages we can thus estimate. In this way we can compare evolutionary rates in different branches of the family. At the same time 44 expansin genes seem to have been lost since the first duplication took place. This analysis can also be extended to the rice genome which contains at least 56 expansin genes. The last common ancestor of Arabidopsis and rice had at least 12 expansin genes of which descendants can be found in both species. In several of these cases there is a still a reasonable degree of synteny between the segments where the Arabidopsis and rice descendants of the ancestral gene are located, facilitating the identification of orthologous sets. Constructs of the different Arabidopsis expansin promoters fused to the Gus gene are allowing us to determine the pattern of expression of these genes. These patterns suggest that some subfamilies are specialized in particular tissue types. In others cases recently duplicated genes have non-overlapping patterns that suggest fast functional divergence. Comparisons with expansins in rice and other species might allow us to determine the functions of the ancestral genes and how these have evolved.