Isolation and characterization of 18 genes encoding alpha- and beta-expansins in wheat (Triticum aestivum L.)

Expansins are thought to be key regulators of cell wall extension during plant growth. In this study, we isolated 18 expansin genes from wheat, nine of which encode alpha-expansins while the other nine code for beta-expansins. The cysteine-rich and tryptophan-rich regions of the deduced amino acid sequences of all 18 expansins were highly conserved. Genomic sequences were obtained for 17 of the genes, and their intron patterns were determined. Four (A, C, D, E) of the six intron positions known in expansin genes from other species were found to be occupied in these wheat expansin genes. Five wheat expansin genes were mapped to chromosomes 1L, 2L, 5L and 6L respectively, by in silico and comparative mapping. The 18 wheat expansin genes were expressed in leaf, root and the developing seed. Moreover, it was demonstrated that four beta-expansin genes were up-regulated in the internode tissue in F1 hybrids, suggesting that changes in the regulation of these genes in hybrid might contribute to the heterosis observed in internode length and plant height. We therefore conclude that expansins are encoded by a multigene family in wheat, and could play important roles in growth and development.