The Regulation of Compound Leaf Development in Tomato

本研究的目的是了解复合叶与简单叶的区别，并阐明形成这种复杂叶形的发育步骤。本分析的出发点是发现KNOTTED1 （KNOX1基因）等1类同源盒基因仅在双子叶和单子叶的单叶顶端的茎尖分生组织（SAM）和未展开的芽中表达，而不在初生叶原基（P0）中表达。这些基因的过度表达足以引起叶裂片和异位分生组织的形成。然而，在番茄复叶产生的SAM中，KNOX1基因（如LeT6和TKN1）既在SAM中表达，也在新生和发育的叶片原基中表达。这表明KNOX1基因可能为番茄叶片原基提供了一定程度的不确定性，从而导致了形态发生阶段的延长和叶片形态的更复杂。本项目将鉴定与LeT6相互作用提供DNA结合特异性和器官特异性基因调控的蛋白，以及LeT6调控的下游靶点。番茄叶片突变的表达分析表明，LeT6启动子上的反式作用因子、LeT6的靶基因以及其他可能在转录调控中充当LeT6伙伴的基因，将有助于鉴定复合叶片发育中的其他关键基因。初步数据表明，LeT6可能调控番茄中PHANTASTICA同源基因的表达，而PHANTASTICA同源基因又可能调控其他KNOX1基因。以下问题将得到解决。像LeT6这样的KNOX1基因的下游靶点是什么？KNOX1基因是否与其他转录因子（TFs）形成复合体？在番茄茎尖中，像LeT6这样的KNOX1基因的水平是如何调控的？在番茄茎部分生组织和叶片中，PHAN调控KNOX1基因表达的作用是什么？在番茄顶端，PHAN和KNOX1基因的表达模式是否互补（如简单产叶顶端所示）？番茄中PHAN的表达是否能预测小叶起始位点（如单叶抗鼻草和拟南芥）？对LeT6、TKN1、PHAN等KNOX1基因及其调控关系的仔细研究，将有助于理解复叶中产生复杂叶形的发育步骤。

Sinha9983063The purpose of this research is to understand how compound leaves differ from simple leaves and to elucidate the developmental steps that give rise to this complex leaf form. The starting point of this analysis is the finding that Class 1 homeobox genes like KNOTTED1 (KNOX1 genes) are expressed only in the shoot apical meristem (SAM) and unexpanded shoots, and not in the incipient leaf primordium (P0), of simple leaf producing apices in both dicots and monocots. Over-expression of these genes is sufficient to cause leaf lobing and ectopic meristem formation. However, in compound leaf producing SAMs in tomato, the KNOX1 genes (like LeT6 and TKN1) are expressed both in the SAM and in emerging and developing leaf primordia. This suggests that KNOX1 genes may provide a degree of indeterminacy to the leaf primordia in tomato, thereby leading to an extended stage of morphogenesis and a more complex leaf form. This project will identify the proteins that interact with LeT6 to provide DNA binding specificity and organ specific gene regulation, and the downstream targets of LeT6 regulation. Expression analyses in the tomato leaf mutations suggest that trans-acting factors at the LeT6 promoter, targets of LeT6, and other genes that may act as LeT6 partners in transcriptional regulation would lead to the identification of other key genes in compound leaf development. Preliminary data suggests that LeT6 may regulate the expression of the PHANTASTICA homolog in tomato, which in turn may regulate other KNOX1 genes. The following questions will be addressed. What are the downstream targets of the KNOX1 genes like LeT6? Do the KNOX1 genes act in a complex with other transcription factors (TFs)? How are the levels of KNOX1 genes like LeT6 regulated in tomato shoot apices? What role does PHAN play in the regulation of KNOX1 gene expression in tomato shoot meristems and leaves? Are the expression patterns of PHAN and KNOX1 genes complementary in tomato apices (as shown for simple leaf producing apices)? Does PHAN expression in tomato predict sites of leaflet initiation (as suggested for the simple leaved Antirrhinum and Arabidopsis)? A careful study of KNOX1 genes like LeT6 and TKN1, PHAN, and their regulatory relationships will allow an understanding of the developmental steps that give rise to the complex leaf form in compound leaves.