Auxin-regulated Organ-and Tissue-Specific Gene Expression

植物激素吲哚乙酸在调节或诱导细胞分裂、伸长和分化等生长发育过程中起关键作用。外源应用这种激素或其合成类似物会导致幼苗或器官中基因表达的快速变化，从而诱导细胞分裂或伸长。Guilfoyle博士描述了多种生长素诱导的mrna，其中一些，如生长素上调的小rna的SAUR，在大豆下胚轴的伸长区域最丰富，也最容易诱导。“组织打印”和原位杂交表明，SAUR基因主要在延长的下胚轴区域的表皮和皮质细胞中表达，此外，mrna在重力刺激的大豆下胚轴的上部和下部迅速重新分布。这些小rna的丰度在施用生长素后2.5分钟内增加，在施用生长素后10分钟内达到最大稳定水平的一半。吉尔福约尔博士已经证明，添加生长素后RNA丰度的增加，至少在一定程度上是由于SAUR基因转录率的提高。另一方面，环己亚胺给药后RNA丰度的增加不涉及转录激活，这表明转录后事件如RNA稳定可能参与其中。最近的研究结果表明，SAUR基因聚集在大豆核基因组中，当整个基因簇通过农杆菌T-DNA转移到矮牵牛植株时，大豆基因被生长素诱导。Guilfoyle博士现在提议1)鉴定赋予SAUR基因生长素诱导性的顺式作用元件，2)分离、纯化和表征与顺式作用元件相互作用的反式作用因子，3)鉴定调节SAUR rna快速更新的顺式作用元件。4)利用杂交和免疫学方法确定生长素和重力诱导的基因在组织、细胞和亚细胞水平上的表达模式；5)研究矮化突变体和向地性突变体是否可能改变SAUR基因的表达模式，以及过量或不足产生生长素诱导的rna的转基因植物的表型。该研究的长期目标是深入了解生长素如何激活特定组织中的特定基因，哪些蛋白质介导生长素诱导的基因激活，以及生长素诱导的基因产物在植物生长发育中起什么作用。

The plant hormone, indoleacetic acid, appears to play key roles in regulating or inducing growth and developmental processes such as cell division, elongation, and differentiation. Exogenous application of this hormone or its synthetic analogs results in rapid changes in gene expression in seedlings or organs that are induced to undergo cell division or elongation. Dr. Guilfoyle has described a variety of auxin-induced mRNAs, and some of these, the SAUR of Small Auxin Up-regulated RNAs, are most abundant and most inducible in elongating regions of soybean hypocotyls. "Tissue printing" and in situ hybridization have been used to show that the SAUR genes are expressed primarily in epidermal and cortical cells of the elongating hypocotyl region, and furthermore, the mRNAs rapidly redistribute within the upper and lower portions of a gravistimulated soybean hypocotyl. The abundance of these small RNAs increases within 2.5 minutes after auxin application to elongating soybean hypocotyl sections, and half maximal steady state levels of these mRNAs are reached within 10 minutes after auxin administration. Dr. Guilfoyle has shown that the increase in RNA abundance after auxin addition results, at least in part, from increased transcription rates on the SAUR genes. On the other hand, an increase in RNA abundance after cycloheximide administration does not involve transcriptional activation, suggesting that post transcriptional events such as RNA stabilization may be involved. Recent results indicate that the SAUR genes are clustered within the soybean nuclear genome, and that the soybean genes are induced by auxin addition when the entire gene cluster is transferred via Agrobacterium T-DNA to petunia plats. Dr. Guilfoyle now proposes to 1) identify the cis-acting elements that confer auxin inducibility to the SAUR genes, 2) isolate, purify, and characterize trans acting factors that interact with the cis acting elements, 3) identify the cis acting elements that regulate the rapid turnover of the SAUR RNAs, 4) determine the patterns of auxin and gravity induced gene expression at the tissue, cellular, and subcellular levels using hybridization and immunological approaches, and 5) examine dwarf and gravitropic mutants for possible altered expression patterns of the SAUR genes and the phenotypes of transgenic plants which overproduce or underproduce the auxin induced RNAs. %%% The long range objectives of the proposed research are aimed at providing insight into how auxin activates specific genes in specific tissues, what proteins mediate the auxin induced gene activation, and what roles the auxin-induced gene products play in plant growth and development.