Molecular Basis of Hormone Antagonism in Cereal Aleurone Cells

赤霉素（GA）和脱落酸（阿坝）这两种植物激素之间的拮抗作用调节植物从种子形成到种子萌发的转变以及其他一些生理和发育过程。 该项目旨在研究大麦种子糊粉层细胞中这种激素拮抗作用的分子基础，其中这两种激素的作用可以通过编码酶（如α-淀粉酶、蛋白酶或一组称为晚期胚胎发生丰富（莱亚）蛋白的独特蛋白质）的标记基因的活性来方便地监测。 GA/阿坝拮抗作用长期以来被认为是非竞争性的，并且已经观察到阿坝在这种拮抗作用中的作用对基因转录过程的抑制剂敏感。 最近的研究结果表明，阿坝诱导的调节分子，蛋白激酶PKABA 1，是一个关键的中间体，在抑制GA调节的基因表达。 本项目的目的是进一步阐明PKABA 1在GA/阿坝拮抗中的作用，并研究其与其他介导GA和阿坝作用的信号转导成分相互作用的机制。 该项目的具体目标包括：1）研究阿坝和GA如何调节PKABA 1的合成，2）确定PKABA 1的表达是否由脂质降解酶磷脂酶D（PLD）（早期阿坝信号转导组分）的活性介导，3）“绘制”PKABA 1与其他已知信号分子的作用位点，4）确定PKABA 1分子的功能结构域，这对于其调节作用是重要的，和5）研究对于GA诱导基因表达重要的调节分子的水平和活性如何受到阿坝处理或PKABA 1的影响。 在执行这一项目时，将采用生物化学、遗传学、细胞和分子生物学技术的多学科方法。 希望这个项目不仅能揭示两组重要的植物激素之间相互作用的分子基础，而且还能揭示植物中独特的蛋白激酶的作用。 由于种子萌发的调节一直是农业中的一个重要问题，因此可以想象，在该项目中获得的信息也可能导致潜在的应用。 除了培训一名博士后研究员和一名研究生外，还预计将有几名本科生参与整个项目。

The antagonism between two phytohormones, gibberellins (GA) and abscisic acid (ABA), regulates the transition from seed formation to seed germination as well as several other physiological and developmental processes in plants. This proposed project is designed to investigate the molecular basis of this hormone antagonism in the aleurone cells of barley seeds, where the action of these two hormones can be conveniently monitored by the activity of several marker genes encoding enzymes such as a-amylases, proteases, or a group of unique proteins called late embryogenesis abundant (LEA) proteins. The GA/ABA antagonism has long been recognized as non-competitive in nature, and it has been observed that the action of ABA in this antagonism is sensitive to inhibitors of the gene transcription process. Recent results suggest that an ABA induced regulatory molecule, the protein kinase PKABA1, is a key intermediate in suppressing the GA-regulated gene expression. The objective of this proposed project is to further elucidate the role of PKABA1 in GA/ABA antagonism and to investigate the mechanisms underlying its interactions with other signal transduction components mediating the action of GA and ABA. The specific aims in this project include: 1) to investigate how ABA and GA regulate the synthesis of PKABA1, 2) to determine whether the expression of PKABA1 is mediated by the activity of a lipid-degrading enzyme, phospholipase D (PLD), an early ABA signal transduction component, 3) to "map" the site of action of PKABA1 in relation to other known signaling molecules, 4) to determine the functional domains of the PKABA1 molecule, which are important for its regulatory roles, and 5) to study how the levels and activities of regulatory molecules important for the GA induction of gene expression can be affected by ABA treatment or PKABA1. A multi-discipline approach employing biochemical, genetic, cell and molecular biology techniques will be followed in carrying out this project. It is hoped that this proposed project would not only reveal new insights into the molecular basis of interactions between two important groups of phytohormones, but also the role of a unique protein kinase in plants. Since regulation of seed germination has been an important problem in agriculture, it is conceivable that the information obtained in this project could also lead to potential applications. In addition to the training of one postdoctoral fellow and one graduate student, the participation of several undergraduate students throughout this project is also anticipated.