Biochemistry and Molecular Biology of Defense Barriers of Plants

植物角质层是植物的最外层，在植物与包括病原真菌在内的环境相互作用中起着重要的作用。植物防御屏障的结构聚合物，角质和木质素，将使用一种新技术，原子力显微镜进行检查，该技术可以提供分子尺度的图像，从而可以首次直接揭示这些复杂聚合物的分子结构。通过直接分离酶和克隆在表皮（角质层成分的合成部位）中独特表达的基因，将阐明参与角质层成分生物合成的酶和基因的性质。真菌侵入植物的分子机制将被阐明。通过阐明受植物信号调控的真菌特有基因的结构、功能和表达调控，研究表皮成分和成熟激素乙烯如何触发真菌分生孢子萌发和分化形成附着胞这一侵染结构。将通过分离结合启动子元件的转录因子和克隆激活转录因子结合的激酶来研究独特的角质素单体酸如何触发真菌角质酶基因表达。在突破表皮屏障后，真菌病原体利用果胶降解酶（包括果胶裂解酶）穿透果胶屏障。通过阐明每个基因表达的条件，并通过评估基因破坏和反义抑制基因表达对病原体毒力的影响，将研究真菌裂解酶基因家族各成员的表达调控在发病机制中的作用。这些研究结果将有助于阐明病原菌与植物防御屏障相互作用的基本机制。操纵这些相互作用可以为植物保护提供新的途径。＊＊＊

9318544 Kolattukudy Plant cuticle, the outermost layer of plants, plays a significant role in the interaction of plants with the environment including pathogenic fungi. The structural polymers of plant defensive barriers, cutin and suberin, will be examined using a new technology, atomic force microscopy, that gives images at molecular dimensions and thus could directly reveal for the first time the molecular architecture of these complex polymers. The nature of the enzymes and genes involved in the biosynthesis of the cuticular components will be elucidated by direct isolation of the enzymes and by cloning genes uniquely expressed in the epidermis, the site of synthesis of the cuticular components. Molecular mechanisms involved in the fungal penetration into plants will be elucidated. How cuticular components and the ripening hormone, ethylene, trigger germination and differentiation of fungal conidia to form appressorium, the infection structure, will be studied by elucidating the structure, function and regulation of expression of the unique fungal genes regulated by the plant signals. How the unique cutin monomer acids trigger fungal cutinase gene expression will be studied by isolating the transcription factors that bind the promoter elements and by cloning the kinases that activate the transcription factor binding. After breaching the cuticular barrier the fungal pathogen penetrates the pectinaceous barriers using pectin degrading enzymes including pectate lyase. The role of regulation of expression of the various members of the family of fungal lyase genes in pathogenesis will be studied by elucidating the conditions under which each gene is expressed and by assessing the effect of inhibition of expression of the genes by gene disruption and antisense on the virulence of the pathogen. The results of the proposed studies will help to elucidate the basic mechanisms involved in the interaction of pathogenic fungi with the defensive barriers of pl ants. Manipulation of these interactions could provide new approaches to plant protection. ***