Identification And Functional Characterization Of Wheat Expansin Genes

The elongation of cell was essential and important to plant growth, and it was enslaved to the extension of cell wall. To control the extension and to rearrange the dynamic structure of cell wall could regualte the plant growth. Expansin was identified as proteins that induce cell wall extension and stress relaxation at acidic pH condition, and participated in diverse plant developmental processes. Up to now, no systematic identifications of genes encoding expansins were reported in wheat. We isolated 3 expansin gene fragments and 18 expansin genes, which contained complete open reading frame by using degenerate primers PCR and in silico cloning. Based on these results, their expression profiles and putative functions were analyzed in this article. The main results are as follows:1) Three expansin gene fragments and 18 expansin genes which contained complete open reading frame were obtained by using degenerate primers PCR and in silico cloning. Based on the phylogenetic analysis, TaEXPAl-TaEXPA9 (GenBank Accessions AY485121 and AY543528- AY543535) represent nine a-expansin genes, while TaEXPBl-TaEXPB5 (Accessions AY543536- AY543540) and TaEXPB7-TaEXPB10 (Accessions AY543541- AY543544) belong to B-expansin. The deduced amino acid sequences of the 18 expansin genes were highly conserved at the cysteines-rich region and tryptophan-rich region.2) Genomic sequences of 17 expansin genes were obtained by using gene specific primers. Previous studies suggested that there were six intron positions in expansin genes in Arabidopsis and rice, namely A, B, C, D, E and F. In this study, four introns, A, C, D and E, could be observed in wheat expansin genes. It was shown that position C and E are present in both a and B-expansin genes in Arabidopsis, rice and wheat. It is presumed that there was a common ancestor of expansin. Since intron positions C and E are present in all expansin genes, these two introns should be present in the ancestor. Intron positions D and F were absent in a-expansin, suggesting that they might occur in B-expansin shortly after a/B-subgroup split. Position A and B were only present in rice and wheat, and were predicted to emerge after monocot/dicot split.3) Five wheat expansin genes(TaEXPA5, TaEXPA7, TaEXPA9, TaEXPB2å’ŒTaEXPB9)were mapped in chromosome 2L, 5L, 1L and 6L respectively by in silico and comparative mapping.4) The 18 wheat expansin genes were expressed in leaf, root and developing seed. Moreover, it was demonstrated that in the internode tissue four expansin genes were up-regulated in hybrid F1, suggesting that over-expression of expansin genes in hybrid might contribute to the heterosis observed in internode length and plant height. Expression of Wheat expansin genes was changed in the seedling by treatment with GA3.5) Transgenetic analysis was carried to study the biological functions of wheat expansin genes obtained in this research. Overexpression of TaEXPAl in Arabidopsis thaliana could enlarge the size of rosette, advance the blossom time and increase the plant height.6) TaEXPB2 was also overexpressed in Arabidopsis thaliana. As compared to the widetype and positive control, the phenotype of transgenic plants shows no obvious changes. Expression of Wheatexpansin genes was changed in the young seedling by treatment with GA3.7) Inverse PCR were done in order to obtain the 5'-UTR unknown sequence of TaEXPAl. There are several candidate motifs in the 5'-UTR sequence of TaEXPAl, including response to stress and several hormones. Based on the result, it is presumed that the expression of TaEXPAl might be regulated by these elements.