Regulatory Mechanisms of Metabolic Signaling in Plants

糖是进化上保守的信号分子，控制着许多重要的发育过程和从细菌、酵母、哺乳动物到植物的生理反应。大量的细胞和转基因研究提供了令人信服的证据表明，植物己糖激酶(HXK)是一种糖结合酶，具有糖感受器的信号和代谢功能。为了进一步阐明植物糖信号网络的分子机制，以拟南芥为模型，采用遗传方法分离了糖反应突变体。基于高糖抑制拟南芥萌发后发育转换的表型分析，已分离到葡萄糖不敏感(GIN)和葡萄糖过敏感(GLO)突变体。这些葡萄糖信号转导突变体及其相应基因的遗传、表型和分子特征为理解营养状态与植物激素生物合成和信号转导的调控机制提供了许多令人惊讶的新见解。目前，与葡萄糖感知和信号传递直接相关的最重要的糖反应突变体是HXK1缺乏的gi2。对其他HXK和HXK-like(HKL)基因的研究，GIN2抑制突变体的鉴定，利用功能基因组工具分析HXK1介导的全球基因表达，以及了解葡萄糖和激素信号通路之间的相互作用，将促进我们对糖信号在植物生长发育中调控作用的分子机制的了解。由于糖的生产和消耗是植物生长、繁殖和贮藏中最基本的活动，并且与环境条件和因素密切相关，了解糖信号网络的分子基础可能有助于设计新的农业改良策略。代谢信号机制的研究也为研究人员、博士后以及研究生和本科生提供了很好的培训机会，特别是来自科学领域中代表性不足的群体。未来的研究计划有四个目标：1)HXK和HXK-like(HKL)基因的功能分析2)GIN2抑制突变体的遗传、表型和分子分析3)HXK调节基因的全球基因表达和功能分析4)阐明葡萄糖和激素信号相互作用的分子机制尽管糖对植物生长和发育的广泛影响已经知道几十年了，但糖信号网络的分子机制直到最近才被发现。糖调节通路直接和广泛地与多种激素、代谢和逆境信号通路相连，并受环境因素的调节，这些环境因子决定了植物适应性和灵活的生长和发育的输出。这些发现对基础和应用科学研究产生了重大影响，并改变了植物代谢调节的传统观念。对我们理解植物生命基本控制的智力贡献将具有实际应用，从改进植物纤维、食品、医药和替代能源和可再生能源的生产，到操纵环境和生态系统，包括调节全球二氧化碳汇。

Sugars are evolutionarily conserved signaling molecules that control many vital developmental processes and physiological responses from bacteria, yeasts, mammals, to plants. Extensive cellular and transgenic studies have provided compelling evidence that plant hexokinase (HXK), a sugar-binding enzyme, acts as a sugar sensor with both signaling and metabolic functions. To further elucidate the molecular mechanisms underlying the plant sugar-signaling network, a genetic approach has been taken to isolate sugar response mutants using Arabidopsis as a plant model. Based on a phenotypic assay in which a high level of glucose blocks the switch of post-germination development in Arabidopsis, both glucose insensitive (gin) and glucose over-sensitive (glo) mutants have been isolated. Genetic, phenotypic and molecular characterizations of these glucose-signaling mutants (gin1, gin2, gin4, gin5 & gin6) and their corresponding genes have provided many surprising new insights into the regulatory mechanisms connecting nutrient status to plant hormone biosynthesis and signaling. Currently, the most important sugar response mutant that is directly linked to glucose sensing and signaling is gin2 with HXK1 deficiency. The study of other HXK and HXK-like (HKL) genes, the characterization of gin2 suppressor mutants, the analysis of HXK1-mediated global gene expression using functional genomic tools, and the understanding of interactions between glucose and hormone signaling pathways will advance our knowledge on the molecular mechanisms underlying the regulatory roles of sugar signals in plant growth and development. Since sugar production and consumption constitutes the most fundamental activities of plant life in growth, reproduction and storage, and is tightly linked to environmental conditions and factors, understanding the molecular basis of sugar signaling network may help design new strategies for improvements in agriculture. The study of metabolic signaling mechanisms also offers excellent training opportunities for researchers, postdoctoral associates and graduate and undergraduate students especially from underrepresented groups in science.Future research plans have four objectives:1) Functional analysis of HXK and HXK-like (HKL) genes2) Genetic, phenotypic and molecular analysis of gin2 suppressor mutants 3) Global gene expression and functional analyses of HXK-regulated genes 4) Elucidation of the molecular mechanisms underlying the interactions between glucose and hormone signalingAlthough the broad effects of sugars on plant growth and development have been known for decades, the molecular mechanisms of sugar signaling network have only been recently discovered. The sugar regulatory pathways are directly and extensively connected to multiple hormonal, metabolic, and stress signaling pathways and are modulate by environmental factors that determine the output of adaptive and flexible growth and development in plants. The discoveries have generated significant impact on basic and applied scientific research and have altered traditional concepts on metabolic regulation in plants. The intellectual contribution to our understanding of fundamental control of plant life will have practical applications from the improved production of plant fiber, food, medicine and alternative and renewable energy resources to the manipulation of environmental and ecological systems including the modulation of global CO2 sinks.