Analysis Of Remote Asymmetric Somatic Hybrids Between Common Wheat And Arabidopsis Thaliana

Common wheat (Triticum aestivum) is a key food crop, but research on its genome analyses is relatively difficult as it has a huge genome (16,000M) and is allohexaploid. Arabidopsis thaliana (2n=10) is an important model plant with small genome of 136Mb. As whole genome sequencing has been completed, A. thaliana has a relatively well understood genetic background. In this paper, callus-derived protoplasts of common wheat (cv. Hesheng 3) irradiated with ultraviolet light (UV) for 30s,1min, and 2min respectively, were fused by using the PEG method with cell suspension-derived protoplasts of Arabidopsis thaliana. The aim was to introduce wheat chromatin, especially the gene-rich regions, into the A. thaliana genome, thus enabling the study of the wheat genome in A. thaliana with a simple genome background. However, we only obtained the asymmetric somatic hybrid and their plantlets similar to the wheat donor parent. Inheritance and variation of the remote somatic hybrid genome was investigated.Three fusion combinations were performed: Combination I , A. thaliana protoplasts + wheat protoplasts irradiated with 380μW/cm~2 UV for 30s; Combination II, A. thaliana protoplasts + wheat protoplasts irradiated with 380μW/cm~2 UV for lmin; Combination III, A. thaliana protoplasts + wheat protoplasts irradiated with 380μW/cm~2 UV for 2min. Protoplasts of A. thaliana and UV treated wheat protoplasts were used as controls, respectively.After 8 weeks of culture in the dark, 4, 22 and 5 regenerated cell lines were obtained from Combination 1, Combination 2 and Combination 3, respectively. In the controls, no cell line regenerated. Two cell lines in Combination I were Arabidopsis-type callus that died after subcultures for two times, while the others resembled wheat callus. In the remaining cell lines, seven of them regenerated green plantlets, while nine of the others regenerated albino shoots. All the green plantlets and albino shoots resembled wheat in morphology.The hybrid nature of eleven cell lines and one plant were confirmed by isozyme, random amplified polymorphic DNA (RAPD), SSR, cytoplasmic genome PCR-RFLP and chromosome analyses. GISH results of some cell lines indicated that 1~3 small chromosome fragments of A. thaliana were found introgression into the terminals of wheat chromosomes, forming highly asymmetric hybrids. The chromosome elimination and introgression in the asymmetric somatic hybridization of remote phylogenetic relationship was discussed.Cytoplasmic genome tests did not show any cytoplasmic genetic materials from A. thaliana. However, variations in four cell lines from the normal wheat cytoplasmic genome were found in chloroplast SSR analyses, indicating recombination or rearrangement occurred during the process of somatic hybridization.Interestingly, a 281bp miniature inverted-repeat transposable element (MITE) related sequence was found by chance in the hybrids, which might be a part of MITE. We believe this sequence still came from nuclear genome, and the transposition of MITE and other transposable elements might have been mobilized in somatic hybridization. Further work will be needed to find out whether somatic hybridization could activated the transposable elements or not and the potential role of such elements during somatic hybridizations.