Teosinte branched and the evolution of development

Doebley 9513573 TeosinteBranchedl（TBL）是玉米的隐性突变体，其使植物具有在上部节处由雄穗顶端的长侧枝和在基部节处的许多分蘖。顾名思义，tbl突变体植物与玉米的野生祖先大刍草有惊人的相似性。 最近，我的实验室确定tbl参与了玉米植物结构（穗尖短侧枝）从大刍草植物结构（穗尖长侧枝）的进化。我们对tbl的模型是，它作为腋分支发育的阻遏物，使得玉米等位基因（Tbl +玉米）产生强阻遏（短分枝），而大刍草等位基因（tbl +大刍草）产生弱阻遏（正常长分枝）。这个模型进一步表明，tbl +大刍草是环境调节，使大刍草的分支伸长的程度是从周围植被的遮光程度的函数。玉米的进化可能涉及tbl表达从环境调节表达到组成型表达的变化。最近，我的实验室使用Mutator转座因子系统克隆了tbl。拟议的研究将利用这个tbl克隆来测试所提出的tbl模型，并阐明tbl中负责玉米从大刍草进化的分子变化的性质。首先，将确定tbl的分子结构，包括核酸序列、内含子-外显子边界以及与其他已知基因的同源性。还将测定tbl的10个玉米拷贝和1个大刍草拷贝的序列。 系统发育和视觉比较这个样品的玉米和大刍草等位基因将允许识别的序列基序，只在玉米中发现，而不是在大刍草。这些基序将是负责Tbl +玉米和tbl +大刍草之间的功能差异的分子事件的候选者。其次，分析Tbl +玉米和tbl +大刍草的表达模式以确定这些等位基因的表达是否不同以及如何不同。在该模型下，tbl +teosinte基因的表达受遮荫程度的影响，而Tbl +Maize基因在所有环境下都有较强的表达。第三，将确定不同tbl等位基因的表型效应。将对tbl和其他两个被认为参与玉米植株结构进化的基因座之间的上位性进行测试。 发育的进化已被确定为未来十年发育生物学的重点。拟议的研究将通过评估基因结构和表达的变化如何改变植物发育的正常过程，从而导致新的成年形式的进化，为理解发育的进化做出重大贡献。拟议的研究还将为植物发育生物学和生物技术做出贡献。本研究为玉米发育相关基因的克隆和结构鉴定提供了基础。tbl基因的克隆和鉴定将为分析植物发育中的分生组织命运和顶端优势提供新的工具。最后，由于顶端优势的增加是植物驯化的共同特征，包括所有谷物、许多树种和草本植物如向日葵，因此存在tbl工程将使作物或树木改良取得新进展的可能性。 3

Doebley 9513573 teosinte branchedl (tbl ) is a recessive mutant of maize that conditions the plant to have long lateral branches tipped by tassels at the upper nodes and many tillers at the basal nodes. As its name implies, tbl mutant plants show a striking similarity to teosinte, the wild progenitor of maize. Recently, my laboratory determined that tbl was involved in the evolution of maize plant architecture (short lateral branches tipped by ears) from teosinte plant architecture (long lateral branches tipped by tassels). Our model for tbl is that it acts as a repressor of axillary branch development such that the maize allele (Tbl +Maize) engenders strong repression (short branches) and the teosinte allele (tbl +teosinte) weak repression (normally long branches). This model further suggests that tbl +teosinte is environmentally regulated so that the extent of branch elongation in teosinte is a function of the degree of shading from surrounding vegetation. The evolution of maize would have involved a change in tbl expression from environmentally regulated expression to constitutive expression. Recently, my laboratory has molecularly cloned tbl using the Mutator transposable element system. The proposed research will utilize this tbl clone to test the proposed model for tbl and to elucidate the nature of the molecular changes in tbl that were responsible for the evolution of maize from teosinte. First, the molecular structure of tbl including nucleic acid sequence, intron-exon borders, and homology to other known genes will be determined. The sequences of 10 maize and 1() teosinte copies of tbl will also be determined. Phylogenetic and visual comparison of this sample of maize and teosinte alleles will allow the identification of sequence motifs that are found only in maize and not in teosinte. These motifs will be candidates for the molecular event(s) responsible for the functional difference between Tbl +Maize and tbl +teosinte. Second, the pattern of expression of Tbl +Maize and tbl +teosinte will be analyzed to determine if and how the expression of these alleles differs. Under the proposed model, the expression of tbl +teosinte should be influenced by the degree of shading, while Tbl +Maize should be strongly expressed under all environments. Third, the phenotypic effects of the different tbl alleles will be determined. Tests for epistasis between tbl and two other loci thought to be involved in the evolution of plant architecture in maize will be made. The evolution of development has been identified as a focus for developmental biology over the next decade. The proposed research will make significant contributions to the understanding of the evolution of development by assessing how changes in gene structure and expression alter the normal course of plant development leading to the evolution of new adult forms. The proposed research will also make contributions to plant developmental biology and biotechnology. This research will provide for the cloning and structural characterization of an important gene involved in maize development. The cloning and characterization of tbl will provide new tools for the analysis of meristem fate and apical dominance, processes of long-standing interest in plant development. Finally, since increased apical dominance is a common feature of plant domestication including all cereals, many tree species and herbs such as sunflower, the possibility exists that engineering of tbl will enable new advances in crop or tree improvement. 3