The miniature1 （mn1） seed phenotype is a loss-of-function mutation at the Mnl locus that encodes a cell wall invertase; its deficiency leads to pleiotropic changes including altered sugar levels and decreased levels...The miniature1 （mn1） seed phenotype is a loss-of-function mutation at the Mnl locus that encodes a cell wall invertase; its deficiency leads to pleiotropic changes including altered sugar levels and decreased levels of IAA throughout seed development. To understand the molecular details of such a sugar-hormone relationship, we have initiated studies on IAA biosynthesis genes in developing seeds of maize. Two tryptophan-dependent pathways of IAA biosynthesis, tryptamine （TAM） and indole-3-pyruvic acid （IPA）, are of particular interest. We report on molecular isolation and characterization of an endosperm-specific ZmTARelatedl （ZmTarl） gene of the IPA branch; we have also reported recently on ZmYucl gene in the TAM branch. Comparative gene expression analyses here have shown that （1） the ZmTarl transcripts were approximately 10-fold higher levels than the ZmYucl; （2） although both genes showed the highest level of expression at 8-12 d after pollination （DAP） coincident with an early peak in IAA levels, the two showed highly divergent （antagonistic） response at 12 and 16 DAP but similar patterns at 20 and 28 DAP in the Mnl and ran1 endosperm. The Western blot analyses for the ZmTAR1 protein, however, displayed disconcordant protein/transcript expression patterns. Overall, these data report novel observations on redundant trp-dependent pathways of auxin biosynthesis in developing seeds of maize, and suggest that homeostatic control of IAA in this important sink is highly complex and may be regulated by both sucrose metabolism and developmental signals.展开更多
文摘The miniature1 （mn1） seed phenotype is a loss-of-function mutation at the Mnl locus that encodes a cell wall invertase; its deficiency leads to pleiotropic changes including altered sugar levels and decreased levels of IAA throughout seed development. To understand the molecular details of such a sugar-hormone relationship, we have initiated studies on IAA biosynthesis genes in developing seeds of maize. Two tryptophan-dependent pathways of IAA biosynthesis, tryptamine （TAM） and indole-3-pyruvic acid （IPA）, are of particular interest. We report on molecular isolation and characterization of an endosperm-specific ZmTARelatedl （ZmTarl） gene of the IPA branch; we have also reported recently on ZmYucl gene in the TAM branch. Comparative gene expression analyses here have shown that （1） the ZmTarl transcripts were approximately 10-fold higher levels than the ZmYucl; （2） although both genes showed the highest level of expression at 8-12 d after pollination （DAP） coincident with an early peak in IAA levels, the two showed highly divergent （antagonistic） response at 12 and 16 DAP but similar patterns at 20 and 28 DAP in the Mnl and ran1 endosperm. The Western blot analyses for the ZmTAR1 protein, however, displayed disconcordant protein/transcript expression patterns. Overall, these data report novel observations on redundant trp-dependent pathways of auxin biosynthesis in developing seeds of maize, and suggest that homeostatic control of IAA in this important sink is highly complex and may be regulated by both sucrose metabolism and developmental signals.
