| The periclinal chimeras obtained by apical grafting in vitro between tuber mustard (Brassica juncea Coss. var. tumida Tsen et Lee) and red cabbage(B. oleracea L. var. capitata L.) previously, were used as the research materials in the present study, which possessed both phenotypic and molecular markers for the different cell lineages. The effects of grafting on the growth and development of chimeras were systematically studied through morphological, cytological, anatomical and molecular analysis. And then, the characteristic and inheritance of grafting variation appeared in the sexual progenies of chimera were explored by genetic investigations. Furthermore, genomic and transcriptomic differential screens were performed to seek the cause for phenotypic variation induced by grafting. Moreover, the exchange of small RNA between the cells of different lineages in grafting was detected by Solexa sequencing, which shed light on the molecular mechanism of grafting variation. The main results were as follows:(1) The grafting between tuber mustard and red cabbage changed the developmental patterns of shoot apical meristem (SAM) of the chimeras TCC and TTC (L1-L2-L3; L1-the outmost cell layer of SAM, L2-the middle cell layer, L3- the innermost layer; T= tuber mustard, C= red cabbage), as well as their vegetative and reproductive organs. In addition, the fates of apical cell-layers were addressed, and the results suggested that all the three layers engaged in the formation and development of almost plant organs together, but their contributions varied in different organs; both L1 and L2 participated in the formation of leaf margin, while only the L3 layer forms the adventitious root. The pollen was mainly derived from L2.(2) The embryogenesis in chimera TCC was significantly impaired by the heterologous L1 layer and resulted in embryo abortion, while L3 had little influence on the fertility of TTC. Anatomical observation ovules showed the cell incompatibility between different lineages in embryo sac might be the reason for embryos abortion. Afterwards, we obtained the selfed progeny of chimera TCC via embryo rescue. Morphological and cytobiological identifications demonstrated that the offspring of chimera TCC and TTC were derived from the linage of red cabbage and tuber mustard, respectively. (3) The sexual progenies of chimera TTC showed remarkable phenotypic variation compared with the tuber mustard, such as the termination of SAM and alteration of leaf profile. Besides, the variations of leaf profile had direction and repeatability. Genetic studies manifested it was nuclear variations and could be inherited following the Mendelian inheritance.(4) No polymorphic divergence was found by the ISSR genome analysis, but the suppression subtractive hybridization exhibited that the expression patterns of many genes were changed by grafting.(5) Specific small RNAs of red cabbage were detected in the reverted tuber mustard from grafting chimera by sRNA sequencing, which suggested the intercellular movement of plant sRNA. And the exchanged sRNA between cells of different lineages in grafted plants might be a considerable agent of grafting variation.In this study, the characters and mechanism of phenotypic variations induced by plant grafting were revealed with the assistance of Brassica chimeras, preliminarily. It provided an appropriate experimental system for the research of plant cell-to-cell interaction, and meanwhile it laid the theoretical basis for the rational application of grafting technology, as well as the generalization of plant grafting breeding.
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