Abstract: Heterosis is defined as the advantage of hybrid performance over its parents in growth and productivity. Previous studies showed that differential gene expression in hybrids and their parents is responsible for the heterosis. Plant hormones, especially GAs are found to be related to heterosis in development of shoot and plant height. However, information on systematic identification and characterization of the differentially expressed genes in shoots of hybrid and their parents are not found, and molecular evidence for the contribution of plant hormone to plant heterosis are also absent. The purpose of this paper was to investigate the differential gene express in stems of hybrid and their parents, and further, to investigate the possible role of genes participating hormone signaling in the formation of heterosis of plant stem. Using a wheat cross combination that exhibited vigorous heterosis in plant height, the differential gene expression in upper-most internode of wheat hybrids and their parents was analyzed by cDNA-AFLP. Ninety-eight differentially expressing cDNA fragments were obtained, which were sequenced and analyzed by Blast-x. Reverse Northern hybridization was performed in order to test the expression pattern of isolated ESTs in hybrid and their parents. The differentially expressed genes included a cdc2 gene and a PAS1 gene, which were induced by GAs and CTKs respec-tively and participated in plant cell division. The cdc2 gene was up-regulated in hybrid while the expression of PAS1 in hybrid was near the higher parent. The differentially expressed genes also included kinase participating in signal transduction, genes in-volved in metabolism and genes related to transcription regulations. It can be inferred that numerous genes were differentially expressed in the upper-most internode of hybrids and their parents, including genes participating in cell division and cell expan-sion, kinase related to signal transduction and so on. Reverse Northern blot analysis indicated that the expression pattern in our cDNA-AFLP analysis is credible. Since it has been much reported that genes participating in cell division and cell expansion are involved in plant stem growth and elongation, and genes that participate in gibberellins signals have been proved to be up-regulated in wheat hybrid and contributed to heterosis in wheat plant height, it can be modestly speculated that the differential expression of genes involved in phytohormone signals may be related to heterosis in wheat intenode elongation and plant height.

Key words: Wheat, Internode, cDNA-AFLP, Differential gene expression