Physiological Role of Sugar-Modulated Gene Expression in Higher Plants

植物生物学的核心是控制光合作用产物在生长组织中的分配的过程。最近的发现表明，这些资源的分布和新陈代谢可能在一定程度上受到响应于碳水化合物供应的基因表达短期变化的调节。蔗糖合成酶是许多依赖进口蔗糖的发育中的植物组织中负责蔗糖水解酶的主要酶。这个实验室已经证明，编码这种酶的基因在玉米根尖的表达受到存在的糖水平的调节。本研究的目的是：1)研究碳水化合物状态在蔗糖合成酶(SH1)基因表达调控中的作用；2)确定SH1基因表达快速变化的生理后果；3)识别其他碳水化合物调控基因。该方法将结合代谢研究和使用基因特异性DNA探针和抗体对基因表达进行量化。这种反应在体内发生的条件将被确定。此外，还将利用玉米蔗糖合成酶和转化酶突变体来评估蔗糖合成酶基因表达的短期变化对代谢的影响。最后，除了蔗糖合成酶之外，这种反应还可能包括其他代谢重要的基因。本研究不仅有助于阐明基因表达与代谢之间的相互作用，而且有助于阐明高等植物蔗糖分配的调控机制。也许这个实验室已经描述了第一个糖调节的已识别植物基因表达的例子。具体地说，SH1形式的蔗糖合成酶在缺乏蔗糖的玉米根尖上被快速和选择性地诱导。蔗糖是大多数物种中糖重新分配的主要形式，因此蔗糖的合成和分解对植物至关重要。蔗糖合成酶催化蔗糖的可逆裂解，因此在输入和代谢蔗糖的组织中是至关重要的。在许多情况下，蔗糖合成酶的活性与蔗糖进入特定组织的程度呈正相关。因此，糖水平与蔗糖合成酶基因表达的相互作用是调节蔗糖输入和利用的潜在机制。本研究从分子水平、细胞水平和植物整体水平详细探讨了糖对蔗糖合成酶表达的调控及其代谢影响。

Central to plant biology are the processes which govern allocation of photosynthetic products among growing tissues. Recent findings indicate that distribution and metabolism of these resources may be regulated in part by short-term alterations of gene expression in response to carbohydrate availability. Sucrose synthase is the primary enzyme responsible for sucrose hydrolysis in many developing plant tissues which depend on imported sucrose. This laboratory has shown that expression of a gene encoding this enzyme in maize root tips is modulated by the level of sugars present. This research goals are to: 1) characterize the role of carbohydrate status in regulation of sucrose synthase (Sh1) gene expression, 2) define the physiological consequences of rapid changes in Sh1 expression, and 3) identify other carbohydrate regulated genes. The approach will combine metabolic studies with quantification of gene expression using gene specific DNA probes and antibodies. The conditions under which this response occurs in vivo will be established. In addition, maize sucrose synthase and invertase mutants will be used to assess the metabolic effects of short- term changes in sucrose synthase gene expression. Finally, the possiblity that this response includes other metabolically important genes in addition to sucrose synthase will be addressed. This research will contribute not only to the clarification of the interplay between gene expression and metabolism, but also to elucidation of mechanisms controlling sucrose allocation in higher plants. Perhaps the first example of sugar-modulated expression of an identified plant gene has been described by this laboratory. Specifically, the Sh1 form of sucrose synthase is rapidly and selectively induced in maize root tips depleted of sucrose. Sucrose is the predominant form in which sugars are redistributed in most species, therefore its synthesis and breakdown are crucial to the plant. Sucrose synthase catalyzes a reversible cleavage of sucrose, and is thus vital in tissues which import and metabolize sucrose. In many instances, sucrose synthase activity is positively correlated with the extent of sucrose movement into a given tissue. Therefore, the interaction of sugar levels with sucrose synthase gene expression is a potential mechanism for regulation of sucrose import and utilization. This research explores sugar regulation of sucrose synthase expression and its metabolic consequences, in detail, at the molecular, cellular, and whole plant levels.