Evolution
Home About Expansins... Protein Structure Expansin Genes abstracts Nomenclature

Expansin genes are present as a multigene family in all land plants examined to date, including angiosperms, gynmosperms, ferns and mosses. There are related genes in slime molds, fungi and bacteria, but whether they encode proteins with classic expansin activity is not yet determined. A very divergent protein with distant relatedness to expansin was also discovered in a nemotode and shown to have expansin-like cell wall creep activity (Qin et al. 2004;   Kudla 2005).  For reviews, see Sampedro and Cosgrove 2005 and Li et al. 2002.

Gene relatedness is usually shown by means of phylogenetic trees. The phylogenetic tree shown below is based on protein sequences for Arabidopsis a- and b-expansins (now given the symbols EXPA and EXPB), plus two families of expansin-like genes (EXLA and EXLB). To fill the tree out, some additional sequences from other species were added to the phylogeny.  The EXPA family is the large gene family in Arabidopsis and rice, followed by the EXPB family and then the EXLA and EXLB families.

By use of synteny (co-linearity of gene order on a chromosomal segment), Sampedro et al. 2005 traces much of the growth of the expansin gene family in Arabidopsis to multiple rounds of whole-genome duplications. Moreover, they identified 17 expansin clades, representing the decendents of 17 ancestral genes found in the last common ancester of rice and Arabidopsis. Very different patterns of gene multiplication were evident for the 17 expansin clades. Some clades remained inglets, others grew to large gene sets. This was markedly the case in rice, where descendents of two ancestral genes represent the majority of expansin genes extant in the rice genome. This analysis was recently extended by analysis of expansins in the poplar genome (Sampedro and Cosgrove 2006).

 

 

This page was last updated on 03/22/06.

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