Homeotic genes and their role in development of wheat's morphological traits

The information concerning major families of plant homeotic genes, ways of their expression regulation and role in plant morphogenesis is outlined. Role of known homeotic genes in wheat development and growth habit establishment is presented. A supposed role of homeotic genes in major morphologic traits formation is discussed.     

花器官形成的基因调控

主要论述了花发育过程中花器官同源异形基因及其相关基因的调控机理。基因调控是一个复杂的 系统,花同源异形基因既受到上游基因的调控,同时又决定了下游基因的表达。对花发育基因调控的研究,不 仅可以从微观水平了解植物花发育的分子机制,同时对花卉等作物的遗传育种也具有重要的指导意义。     

花同源异型MADS-box基因在被子植物中的功能保守性和多样性

MADS-box基因家族成员作为转录调控因子在被子植物花发育调控中发挥关键作用。本文以模式植物拟南芥（Arabidopsis thaliana）和水稻（Oryza sativa）为例,综述了近10年来对被子植物（又称有花植物）两大主要类群——核心真双子叶植物和单子叶植物花同源异型MADS-box基因的研究成果,分析MADS-box基因在被子植物中的功能保守性和多样性,同时探讨双子叶植物花发育的ABCDE模型在多大程度上适用于单子叶植物。     

Homeotic genes have specific functional roles in the establishment of the Drosophila embryonic peripheral nervous system.

The Drosophila embryonic peripheral nervous system (PNS) contains segment-specific spatial patterns of sensory organs which derive from the ectoderm. Many studies have established that the homeotic genes of Drosophila control segment specific characteristics of the epidermis, and more recently these genes have also been shown to control gut morphogenesis through their expression in the visceral mesoderm (Tremml, G. and Bienz, M. (1989), EMBO J. 8, 2677-2685). We report here the roles of homeotic genes in establishing the spatial patterns of sensory organs in the embryonic PNS. The PNS was examined in embryos homozygous for mutations in the homeotic genes Sex combs reduced (Scr), Antennapedia (Antp), Ultrabithorax (Ubx), abdominal-A (abd-A) and Abdominal-B (Abd-B) with antibodies that label specific subsets of sensory organs. Our results suggest that the homeotic genes have specific roles in establishing the correct spatial patterns of sensory organs in their normal domains of expression. In addition, we also report the effects of ectopic expression of the homeotic genes labial (lab), Deformed (Dfd), Scr, Antp or Ubx on the normal development of sensory organs in the embryonic PNS. Interestingly, while previous studies have concluded that ectopic expression of the homeotic genes Dfd, Scr and Antp has no effect on the segmental identity of the abdominal segments, our results demonstrate that this is not true. We show that ectopic expression of these genes does result in the disruption of the developing PNS in the abdomen. Our results are suggestive of a role for the homeotic gene products in regulating genes which are necessary for generating sensory progenitor cells in the developing PNS.     

花同源异型MADS-box 基因在被子植物中的功能保守性和多样性

MADS-box基因家族成员作为转录调控因子在被子植物花发育调控中发挥关键作用。本文以模式植物拟南芥(Arabidopsis thaliana) 和水稻 (Oryza sativa)为例, 综述了近10年来对被子植物(又称有花植物)两大主要类群——核心真 双子叶植物和单子叶植物花同源异型MADS-box基因的研究成果, 分析MADS-box基因在被子植物中的功能保守性和多样性,同时探讨双子叶植物花发育的ABCDE模型在多大程度上适用于单子叶植物。     

Identification of Homeotic Target Genes in Drosophila Melanogaster Including Nervy, a Proto-Oncogene Homologue

In Drosophila, the specific morphological characteristics of each segment are determined by the homeotic genes that regulate the expression of downstream target genes. We used a subtractive hybridization procedure to isolate activated target genes of the homeotic gene Ultrabithorax (Ubx). In addition, we constructed a set of mutant genotypes that measures the regulatory contribution of individual homeotic genes to a complex target gene expression pattern. Using these mutants, we demonstrate that homeotic genes can regulate target gene expression at the start of gastrulation, suggesting a previously unknown role for the homeotic genes at this early stage. We also show that, in abdominal segments, the levels of expression for two target genes increase in response to high levels of Ubx, demonstrating that the normal down-regulation of Ubx in these segments is functional. Finally, the DNA sequence of cDNAs for one of these genes predicts a protein that is similar to a human proto-oncogene involved in acute myeloid leukemias. These results illustrate potentially general rules about the homeotic control of target gene expression and suggest that subtractive hybridization can be used to isolate interesting homeotic target genes.     

Ectopic expression of a single homeotic gene, the Petunia gene green petal, is sufficient to convert sepals to petaloid organs.

Genetic studies in Arabidopsis and Antirrhinum showed that petal determination requires the concomitant expression of two homeotic functions, A and B, whereas the A function alone determines sepal identity. The B function is represented by at least two genes. The Petunia homeotic gene green petal (gp) is essential for petal determination as demonstrated by a Petunia gp mutant that has sepals instead of petals. We have used ectopic expression of the gp gene as a tool to study flower development in Petunia. CaMV 35S-gp expression leads to homeotic conversion of sepals into petaloid organs when expressed early in development. This demonstrates that a single homeotic gene is sufficient to induce homeotic conversion of sepals to petals, suggesting that other petal determining genes are regulated in part by ectopically expressed gp. Indeed, two other MADS-box-containing genes, pmads 2 and fbp 1, which show homology to the Antirrhinum B function gene globosa, are activated in the converted petal tissue. Furthermore, our data provide evidence for autoregulation of gp expression in the petaloid tissue and uncover the role of gp in fusion of petal tissues.     

Ectopic gene expression and homeotic transformations in arthropods using recombinant Sindbis viruses

BACKGROUND: The morphological diversity of arthropods makes them attractive subjects for studying the evolution of developmental mechanisms. Comparative analyses suggest that arthropod diversity has arisen largely as a result of changes in expression patterns of genes that control development. Direct analysis of how a particular gene functions in a given species during development is hindered by the lack of broadly applicable techniques for manipulating gene expression. RESULTS: We report that the Arbovirus Sindbis can be used to deliver high levels of gene expression in vivo in a number of non-host arthropod species without causing cytopathic effects in infected cells or impairing development. Using recombinant Sindbis virus, we investigated the function of the homeotic gene Ultrabithorax in the development of butterfly wings and beetle embryos. Ectopic Ultrabithorax expression in butterfly forewing imaginal discs was sufficient to cause the transformation of characteristic forewing properties in the adult, including scale morphology and pigmentation, to those of the hindwing. Expression of Ultrabithorax in beetle embryos outside of its endogenous expression domain affected normal development of the body wall cuticle and appendages. CONCLUSIONS: The homeotic genes have long been thought to play an important role in the diversification of arthropod appendages. Using recombinant Sindbis virus, we were able to investigate homeotic gene function in non-model arthropod species. We found that Ultrabithorax is sufficient to confer hindwing identity in butterflies and alter normal development of anterior structures in beetles. Recombinant Sindbis virus has broad potential as a tool for analyzing how the function of developmental genes has changed during the diversification of arthropods.     

Function of the apetala-1 gene during Arabidopsis floral development.

We have characterized the floral phenotypes produced by the recessive homeotic apetala 1-1 (ap1-1) mutation in Arabidopsis. Plants homozygous for this mutation display a homeotic conversion of sepsis into brachts and the concomitant formation of floral buds in the axil of each transformed sepal. In addition, these flowers lack petals. We show that the loss of petal phenotype is due to the failure of petal primordia to be initiated. We have also constructed double mutant combinations with ap1 and other mutations affecting floral development. Based on these results, we suggest that the AP1 and the apetala 2 (AP2) genes may encode similar functions that are required to define the pattern of where floral organs arise, as well as for determinate development of the floral meristem. We propose that the AP1 and AP2 gene products act in concert with the product of the agamous (AG) locus to establish a determinate floral meristem, whereas other homeotic gene products are required for cells to differentiate correctly according to their position. These results extend the proposed role of the homeotic genes in floral development and suggest new models for the establishment of floral pattern.     

Unique morphological changes in plant pathogenic phytoplasma-infected petunia flowers are related to transcriptional regulation of floral homeotic genes in an organ-specific manner

Abnormal flowers are often induced by infection of certain plant pathogens, e.g. phytoplasma, but the molecular mechanisms underlying these malformations have remained poorly understood. Here, we show that infection with OY-W phytoplasma (Candidatus Phytoplasma asteris, onion yellows phytoplasma strain, line OY-W) affects the expression of the floral homeotic genes of petunia plants in an organ-specific manner. Upon infection with OY-W phytoplasma, floral morphological changes, including conversion to leaf-like structures, were observed in sepals, petals and pistils, but not in stamens. As the expression levels of homeotic genes differ greatly between floral organs, we examined the expression levels of homeotic genes in each floral organ infected by OY-W phytoplasma, compared with healthy plants. The expression levels of several homeotic genes required for organ development, such as PFG, PhGLO1 and FBP7, were significantly downregulated by the phytoplasma infection in floral organs, except the stamens, suggesting that the unique morphological changes caused by the phytoplasma infection might result from the significant decrease in expression of some crucial homeotic genes. Moreover, the expression levels of TER, ALF and DOT genes, which are known to participate in floral meristem identity, were significantly downregulated in the phytoplasma-infected petunia meristems, implying that phytoplasma would affect an upstream signaling pathway of floral meristem identity. Our results suggest that phytoplasma infection may have complex effects on floral development, resulting in the unique phenotypes that were clearly distinct from the mutant flower phenotypes produced by the knock-out or the overexpression of certain homeotic genes.