| Polarity establisloment occurs in the whole life of plants from embryo to lateral organs. The abaxial-adaxial polarity is one of common features of most lateral organs that initiate from the shoot apical meristem (SAM). Analysis of mutants and identification of related genes on lateral organs provided important clues to understand the molecular mechanism of the polarity establishment. Previous study on the establishment of the abaxial-adaxial axis are mainly focused in the dicots. In contrast, a little is known on the monocots because of limited available mutants. Wheat is one of the important cereals in the world and the molecular mechanism of polarity establishment in this crop still remains uncovered. In this study, we isolated the two genes TaFIL and TaCRC from the spikelets and the carpels of wheat, respectively and further analyzed their functions. Our data may provide some information on the molecular mechanism of the abaxial-adaxial polarity determination. Isolation and characterization of TaFIL and TaCRCTo investigate the molecular mechanism of abaxial-adaxial polarity in wheat, we isolated full length cDNAs of TaFIL and TaCRC from the young spikelets and the carpels, respectively. The full length cDNA of TaFIL is 1216bp, encodeing protein with 297 amino acid residues. The full length cDNA of TaCRC is 1103bp, encoding 199 amino acid residues. Both of the proteins have zinc finger-like domain in N terminus and YABBY domain in C terminus. Sequences analysis indicates that TaFIL and TaCRC belong to the FIL subfamily and the DL/CRC subfamily, respectively.2. TaFIL and TaCRC expression patternsTaFIL mRNA was detected in the young spikelets and carpels, but was not detected in the vegatative organs and other flower organs. TaCRC mRNA was accumulated only in the carpels. The results indicate that both genes may play important roles during floral development in wheat.3. Phenotype analysis of ectopic expression of TaFIL and TaCRC in Arabidopsis To understand the roles of TaFIL and TaCRC in development of the lateral organs, transgenic plants were generated with ectopic expression of TaFIL and TaCRC under the 35S promoter in Arabidopsis. Transgenic plants of TaFIL and TaCRC had different phenotypes.Through analysis of the scanning electron micrographs, the chracterastics of the epidermal cells in the adaxial side of the 35S::TaFIL transgenic leaves were partly inclined to chracterastics of the abaxial side of the wild-type leaves. By the transverse sections, no abnormal morphology was observed in the palisade mesophyll and spongy mesophyll of leaves.The 35S:: TaFIL transgenic cotyledons and the rosette leaves curled towards the abaxial surface dramatically. To investigate the mechanism of curling in leaves, the ratios of adaxial to abaxial epidermal cell numbers were compared in curled and wild-type rosette leaves. Cells of the leaves in transgenic plants and wild type plants were counted from transverse sections. It is indicates that there is cell division defect in the leaves of ectopic expression of TaFIL. In contrast to the densely cytoplasmic cells of wild-type SAM, 35S::TaFIL transgenic SAM consists of the vacuolated cells. Some of the transformants of 35S::TaFIL only generated two cotyledons and had no leaf primordia.Alterations in morphology had been found in both the leaves and carpels of transgenic plants with ectopic expression of TaCRC. The transgenic plants exhibited wider and shorter carpels than the wild-type plants from the flower organs formed until the siliques matured. Similar to the phenotype of the leave of the 35S::TaFIL, the leaves of transgenic plants appeared to be mixture of abaxial and adaxial cells types.4. Conservation of Function in YABBY gene familyThe amino acid sequence alignment and the phenotype analysis indicate that TaFIL and TaCRC are the members of the YABBY gene family, separately beloning to the FIL subfamily and the CRC subfamily. In FIL subfamily, the phenotype of the ectopic expression of TaFIL under the 35S promoter in Arabidopsis resembled...
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