Molecular mechanism of the acquirement and restriction of differentiation potency in plant cells

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1.Analysis of the acquirement of pluripotency of transdifferentiation of isolated mesophyll cellsWe isolated 12 cDNA clones whose transcripts are expressed preferentially in isolated Zinnia mesophyllcells. These clones were divided into teree groups, 1)wound or infection-induced genes, 2)genes encoding proteins involved in protein synthesis, and 3) others. mRNAs for all of these clones were induced by wounding within 12 h of culture but thereafter chenged in hormone-dependent manners, suggesting that the early process involves the activation of protein synthesis.2.Analysis of the restriction of the potency of differentiationa) Analysis of tracheary element precursor cell-specific expression of TED3 promoterThe analysis of transgenic Arabidopsis with chimeric genes of TED3 promoter and GUS gene indicated that this promoter directed tracheary element precursor cell-specific expression.b) Analysis of TED3 functionWe introduced an antisense DNA of TED3 gene into Zinnia leaves and induced many transformed hairy roots. Among the root clones, clones in which the accumulation of TED3 mRNAs were suppressed showed the inhibition of root growth. Taking together with the expression of TED3 mRNAs is localized in tracheary element precursor cells, we presented a hypothesis that TED3 product may be responsible for the elongation of tracheary elements.c)Analysis of cell death processWe isolated cDNA clones for cysteine protease and DNase which may be involved in autolytic process in differentiating tracheary elements. The mRNAs for these clones expressed in very similar pattern, transiently just before vacuole disruption. This suggests a common mechanism of gene expression in relation to cell death process.Based on these results, we presented a hypothesis on the Change in the potency of differentiation.