Distinct structural domains in the planarian brain defined by the expression of evolutionarily conserved homeobox genes

 Homeobox genes such as orthodenticle in Drosophila and its mouse homologues, Otx1 and Otx2, are known to be essential for rostral brain development. To investigate the molecular basis of brain evolution, we searched for otd/Otx-related homeobox genes in the planarian Dugesia japonica, and identified two genes, DjotxA and B, whose expression appears to be restricted to the cephalic ganglion (brain). DjotxA was expressed more medially, in the region containing the termini of the visual axons, and in the visual cells, suggesting involvement in establishment of the visual system. DjotxB was expressed in a discrete region just lateral to the DjotxA-positive domain, but not in the more lateral branch structures, which in turn are characterized by the expression of Djotp, a planarian homeobox gene related to mouse Orthopedia (Otp). In transverse sections of planarians, DjotxA and B expression were observed only at the anterior ends of the stumps, corresponding to the regional pattern of the regenerating brain. Our findings suggest that the planarian brain is composed of structurally distinct and functionally diverse domains which are defined by the discrete expression of the three evolutionarily conserved homeobox genes. Received: 17 June 1998 / Accepted: 20 August 1998     

Three knotted1-like homeobox genes in Arabidopsis

Five arabidopsis kn1-like homeobox genes were cloned through low-stringency screening of Arabidopsis cDNA libraries with the kn1 homeobox from maize. These five genes were named KNAT1-5 (for kn1-like Arabidopsis thaliana). An analysis of KNAT1 and 2 has been presented previously [19]. Here we present an analysis of the genes KNAT3, 4 and 5. On the basis of sequence and expression patterns, these three genes belong to the class II subfamily of kn1-like homeobox genes [16]. Low-stringency Southern analysis suggests several additional members of the class II genes exist in the Arabidopsis genome. The predicted amino acid sequences of the three genes share extensive homology outside of the homeodomain, including 84% between KNAT3 and KNAT4. Northern analysis shows that although all three genes are expressed in all tissues examined, the level of KNAT3 RNA is highest in young siliques, inflorescences and roots, KNAT4 RNA level is strongest in leaves and young siliques, and KNAT5 RNA level is highest in roots. The specificity of these patterns was confirmed by RNA fingerprint analysis. KNAT3 and 4 are light-regulated as they show reduced expression in etiolated seedlings and also in hy3, cop1 and det1 mutant backgrounds.     

New approaches to control plant parasitic nematodes

Plant parasitic nematodes are a serious threat for crop production worldwide. This review summarizes our understanding of plant nematode interactions and presents new alternatives for nematode control in the field. Breeding for resistance has been a major goal for many important crop species like soybean, potato, tomato and sugar-beet. As a result numerous nematode-resistance genes have been identified, two of which have been cloned recently, Hs1 ^pro-1 from sugar-beet, giving resistance to the beet cyst nematode Heterodera schachtii, and Mi from tomato, giving resistance to the root-knot nematode Meloidogyne incognita. Also artificial resistance genes, coding for nematotoxic proteins or causing rapid death of feeding cells, have been elucidated. In the future, genetic engineering of nematode resistance will become more and more important for plant breeding. Transformation techniques will allow genes to be quickly introduced into susceptible breeding lines and then combined with each other to produce plant varieties with durable resistance. Received: 26 August 1998 / Received revision: 16 December 1998 / Accepted: 21 December 1998     

The PBC domain contains a MEINOX domain: Coevolution of Hox and TALE homeobox genes?

 A recent survey of TALE superclass homeobox genes revealed a new domain upstream of the homeodomain that is conserved between the plant KNOX genes and the animal MEIS genes. At the same time, another paper identified the Drosophila gene homothorax (hth) as a homologue of the vertebrate MEIS genes, which prompted a reexamination of the sequences of the MEIS, KNOX (collectively named MEINOX) and PBC domains. Similarity of the complete MEINOX domain was found within the PBC domain. This suggests that the PBC class genes were also derived from the ancient MEINOX genes. Recently, it has been shown that the MEIS genes can interact with the Abd-B genes, whilst previous results have shown that the PBC genes interact with anterior Hox genes. This leads to the hypothesis that the duplication of an ancestral MEINOX gene into the PBC and MEIS genes happened at a point in time when the first two Hox cluster genes, an anterior one and a posterior one, emerged, and that subsequently these gene classes coevolved. Received: 19 January 1998 / Accepted: 11 February 1998     

Increased salt tolerance with overexpression of cation/proton antiporter 1 genes: a meta‐analysis

Cation/proton antiporter 1 (CPA1) genes encode cellular Na⁺/H⁺ exchanger proteins, which act to adjust ionic balance. Overexpression of CPA1s can improve plant performance under salt stress. However, the diversified roles of the CPA1 family and the various parameters used in evaluating transgenic plants over‐expressing CPA1s make it challenging to assess the complex functions of CPA1s and their physiological mechanisms in salt tolerance. Using meta‐analysis, we determined how overexpression of CPA1s has influenced several plant characteristics involved in response and resilience to NaCl stress. We also evaluated experimental variables that favour or reduce CPA1 effects in transgenic plants. Viewed across studies, overexpression of CPA1s has increased the magnitude of 10 of the 19 plant characteristics examined, by 25% or more. Among the ten moderating variables, several had substantial impacts on the extent of CPA1 influence: type of culture media, donor and recipient type and genus, and gene family. Genes from monocotyledonous plants stimulated root K⁺, root K⁺/Na⁺, total chlorophyll, total dry weight and root length much more than genes from dicotyledonous species. Genes transformed to or from Arabidopsis have led to smaller CPA1‐induced increases in plant characteristics than genes transferred to or from other genera. Heterogeneous expression of CPA1s led to greater increases in leaf chlorophyll and root length than homologous expression. These findings should help guide future investigations into the function of CPA1s in plant salt tolerance and the use of genetic engineering for breeding of resistance.     

Comparative genomics of Lbx loci reveals conservation of identical Lbx ohnologs in bony vertebrates

Background  

Lbx/ladybird genes originated as part of the metazoan cluster of Nk homeobox genes. In all animals investigated so far, both the protostome genes and the vertebrate Lbx1 genes were found to play crucial roles in neural and muscle development. Recently however, additional Lbx genes with divergent expression patterns were discovered in amniotes. Early in the evolution of vertebrates, two rounds of whole genome duplication are thought to have occurred, during which 4 Lbx genes were generated. Which of these genes were maintained in extant vertebrates, and how these genes and their functions evolved, is not known.     

Characterization and expression analysis of TERMINAL FLOWER1 homologs from cultivated alloteraploid cotton (Gossypium hirsutum) and its diploid progenitors

The seasonal cycle and persistence of a plant is governed by a combination of the determinate or indeterminate status of shoot and root apical meristems. A perennial plant is one in which the apical meristem of at least one of its shoot axes remains indeterminate beyond the first growth season.TERMINAL FLOWER1 (TFL1) genes play important roles in regulating flowering time, the fate of inflorescence meristem and perenniality. To investigate the role of TFL1-like genes in the determination of the apical meristems in an industrially important crop cultivated for its fibers, we isolated and characterized two TFL1 homologs (TFL1a and TFL1b) from tetraploid cultivated cotton (Gossypium hirsutum) and its diploid progenitors (Gossypium arboreum and Gossypium raimondii). All isolated genes maintain the same exon–intron organization. Their phylogenetic analysis at the amino acid level confirmed that the isolated sequences are TFL1-like genes and collocate in the TFL1 clade of the PEBP protein family. Expression analysis revealed that the genes TFL1a and TFL1b have slightly different expression patterns, suggesting different functional roles in the determination of the meristems. Additionally, promoter analysis by computational methods revealed the presence of common binding motifs in TFL1-like promoters. These are the first reported TFL1-like genes isolated from cotton, the most important crop for the textile industry.     

植物同源异型枢基因的研究进展

植物同源异型枢基因是涉及到植物个体发育的一类重要转录因子编码基因.这类基因及其编码蛋白的结构具有明显的保守性,在植物中广泛存在,研究这类基因,对于揭示植物的发育机制具有重要意义.     

Something fishy in the rat brain: molecular genetics of the hypothalamo-neurohypophysial system

The brain peptides vasopressin and oxytocin play crucial roles in the regulation of salt and water balance. The genes encoding these neurohormones are regulated by cell-specific and physiological cues, but the molecular mechanisms remain obscure. New strategies, involving the introduction of rat transgenes into rats, are being used to address these issues,⁽¹⁾ but the complexity of the rat genome has hampered progress. By contrast, the pufferfish, Fugu rubripes, has a “junk-free” genome.⁽²⁾ The oxytocin homologue from Fugu, isotocin, has been introduced into rats⁽³⁾ and is expressed in oxytocin neurons, where it is upregulated by physiological perturbations that upregulate the oxytocin gene. The Fugu and rat lineages separated 400 million years ago, yet the mechanisms that regulate the isotocin and oxytocin genes have been conserved. Fugu genome analysis and transgenesis in the physiologically tractable rat host are a powerful combination that will enable the identification of fundamental components of the neural systems that control homeostasis. BioEssays 20 :741–749, 1998. © 1998 John Wiley & Sons, Inc.