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| Embryogenic callus induced from petioles of alfalfa (Medicago sativa L. cv. Jinnan) and maintained on kinetin (KN)-containing B5h medium becomes non-embryogenic with differentiation of tracheary elements when kinetin in the medium is replaced by thidiazuron (TDZ). To investigate the molecular mechanisms underlying the TDZ-induced morphological competence transition, we cloned the differentially expressed sequence tags (ESTs) from TDZ-treated callus of alfalfa using suppression subtractive hybridization (SSH). The expression patterns of genes induced by TDZ were found to change throughout the process of TDZ treatment. A homeodomain-leucine zipper protein gene, MSHB1, which was induced by TDZ, may be a transcription factor in the TDZ-regulation of alfalfa callus differentiation. The induction of trehalose-6-phosphate phosphatase (TPP), which may decrease the level of trehalose-6-phosphate, and the induction of 1-aminocyclopropane-1-carboxylate synthase (ACS), which increases the level of ethylene, by TDZ may be responsible for the termination of somatic embryogenesis. |
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| Keywords:Medicago sativa, Suppression subtractive hybridization, Thidiazuron |
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