Morphological analysis of female gametophyte development in the bel1 stk shp1 shp2 mutant

Abstract

In Arabidopsis thaliana, cell fate in developing ovules is determined by the action of the homeodomain factor BELL1 (BEL1) and of the MADS-box factors SEEDSTICK (STK), SHATTERPROOF1 (SHP1) and SHP2. The analysis of the bel1 and the stk shp1 shp2 mutants revealed that the functional megaspore is formed, however, it does not proceed into megagametogenesis. In the bel1 stk shp1 shp2, quadruple mutant megasporogenesis does not take place. In this article we describe a detailed morphological analysis of the quadruple mutant, and we discuss the possibility that BELL1, STK, SHP1 and SHP2 not only control integument identity determination and development, but that they might also play a role during megasporogenesis.     

Collagen gene construction and evolution

Summary Collagen genes appear to have been assembled by the tandem repetition of homologous primary (9 base pair), secondary (54 base pair), and tertiary (702 base pair) modules. In vertebrate interstitial collagen genes many of the secondary modules are separated by introns, but in invertebrate collagen genes the non-coding sequences lie near the ends of supposed tertiary modules and are therefore about 702 (54×13) base pairs apart. The genes for vertebrate interstitial collagens (types I–III) seem to have been constructed by the tandem repetition of five tertiary modules, three of which were subsequently shortened by internal deletions. This shortening of the gene resulted in the non-integral relationship between the period of the fibrils and the length of the molecules of vertebrate collagens, and was therefore responsible for the mechanical properties of the completed product. Comparisons of the amino acid sequences of various collagens indicate that the main types of collagen evolved about 800–900 million years ago, a date that agrees well with the fossil record of primitive Metazoa.     

Plant action: Multiple levels of regulation

This lecture is devoted to the relative contribution of various levels of regulation of the actin cytoskeleton functioning in the cell. Regulation at the levels of gene expression, mRNA and protein synthesis and stability, processes of actin polymerization/depolymerization and actin structures reorganization is briefly considered. Novel information about the pathways of signal transduction to the actin cytoskeleton with the involvement of Arp2/3 complex and RIC proteins is highlighted.     

Interrelationships of Staphyliniform groups inferred from 18S and 28S rDNA sequences, with special emphasis on Hydrophiloidea (Coleoptera, Staphyliniformia)

The series Staphyliniformia is one of the mega‐diverse groups of Coleoptera, but the relationships among the main families are still poorly understood. In this paper we address the interrelationships of staphyliniform groups, with special emphasis on Hydrophiloidea and Hydraenidae, based on partial sequences of the ribosomal genes 18S rDNA and 28S rDNA. Sequence data were analysed with parsimony and Bayesian posterior probabilities, in an attempt to overcome the likely effect of some branches longer than the 95% cumulative probability of the estimated normal distribution of the path lengths of the species. The inter‐family relationships in the trees obtained with both methods were in general poorly supported, although most of the results based on the sequence data are in good agreement with morphological studies. In none of our analyses a close relationship between Hydraenidae and Hydrophiloidea was supported, contrary to the traditional view but in agreement with recent morphological investigations. Hydraenidae form a clade with Ptiliidae and Scydmaenidae in the tree obtained with Bayesian probabilities, but are placed as basal group of Staphyliniformia (with Silphidae as subordinate group) in the parsimony tree. Based on the analysed data with a limited set of outgroups Scarabaeoidea are nested within Staphyliniformia. However, this needs further support. Hydrophiloidea s.str., Sphaeridiinae, Histeroidea (Histeridae + Sphaeritidae), and all staphylinoid families included are confirmed as monophyletic, with the exception of Hydraenidae in the parsimony tree. Spercheidae are not a basal group within Hydrophiloidea, as has been previously suggested, but included in a polytomy with other Hydrophilidae in the Bayesian analyses, or its sistergroup (with the inclusion of Epimetopidae) in the parsimony tree. Helophorus is placed at the base of Hydrophiloidea in the parsimony tree. The monophyly of Hydrophiloidea s.l. (including the histeroid families) and Staphylinoidea could not be confirmed by the analysed data. Some results, such as a placement of Silphidae as subordinate group of Hydraenidae (parsimony tree), or a sistergroup relationship between Ptiliidae and Scydmaenidae, appear unlikely from a morphological point of view.     

Detection of Raillietina saudiae from the domestic pigeon in Saudi Arabia through 18S and 28S rDNA genes

Raillietina saudiae is a well-studied avian gastrointestinal parasite belonging to the family Davaineidae and is the most prevalent cyclophyllid tapeworm infecting pigeon in Saudi Arabia. The present study considered as a complementary analysis of Al-Quraishy et al. (2019; Parasitol Int 71 , 59–72) with molecular studies for two ribosomal DNA genes employed for precise recognition of this Raillietina species. The annotated partial 18S and 28S rDNA gene regions were found to be 888 and 900 bp long that utilized further to elucidate their genetic relationships at species level using maximum likelihood method. The query sequence of R. saudiae is well aligned and placed within the Davaineidae family, with the same clade of all species of Raillietina that well separated from other cyclophyllidean cestodes especially taeniid and hymenolepid species. Sequence data recorded the monophyly of Raillietina species. The current phylogeny supports the usage of the partial 18S and 28S rDNA genes as reliable markers for phylogenetic reconstructions.     

Cold induction of EARLI1, a putative Arabidopsis lipid transfer protein, is light and calcium dependent

As sessile organisms, plants must adapt to their environment. One approach toward understanding this adaptation is to investigate environmental regulation of gene expression. Our focus is on the environmental regulation of EARLI1, which is activated by cold and long‐day photoperiods. Cold activation of EARLI1 in short‐day photoperiods is slow, requiring several hours at 4 °C to detect an increase in mRNA abundance. EARLI1 is not efficiently cold‐activated in etiolated seedlings, suggesting that photomorphogenesis is necessary for its cold activation. Cold activation of EARLI1 is inhibited in the presence of the calcium channel blocker lanthanum chloride or the calcium chelator EGTA. Addition of the calcium ionophore Bay K8644 results in cold‐independent activation of EARLI1. These data suggest that EARLI1 is not an immediate target of the cold response, and that calcium flux affects its expression. EARLI1 is a putative secreted protein and has motifs found in lipid transfer proteins. Over‐expression of EARLI1 in transgenic plants results in reduced electrolyte leakage during freezing damage, suggesting that EARLI1 may affect membrane or cell wall stability in response to low temperature stress.     

Putative candidate genes for blood pressure control in the SHR.BN-RNO8 congenic substrains

The SHR-Lx congenic strain carrying a differential segment of chromosome 8 of BN and PD origin was recently shown to exhibit a significant decrease in blood pressure as compared to the SHR strain. There were two positional candidate genes for blood pressure control mapped to the differential segment: the rat kidney epithelial potassium channel gene (Kcnj1) and brain dopamine receptor 2 gene (Drd2). Bot these genes were separated into SHR.BN-RNO8 congenic substrains. In this communication, we are presenting the assignment of two further putative candidate genes, which might be involved in blood pressure control to the BN/PD differential segment of the SHR-Lx congenic strain. These are: the gene coding for smooth muscle cell specific protein 22 (Sm22) defined by the D8Mcw1 marker and neuronal nicotinic acetylcholine receptor gene cluster, defined by the D8Bord1 marker. Moreover, the glutamate receptor gene Grik4 which also maps to the differential segment of the SHR-Lx should be taken into account. The genetic separation of all these putative candidate genes of blood pressure control is being performed by recombinations and subsequent selection using (SHR×SHR-Lx) intercross population.     

Conservation of rDNA inPolystichum (Dryopteridaceae)

Restriction site variation in the nuclear 18S–25S ribosomal RNA genes (rDNA) was analyzed hierarchically in a species complex in the fern genusPolystichum. Two distinct rDNA repeat types were present in all individuals ofPolystichum examined. No variation was detected among individuals within a population ofP. munitum, among populations ofP. munitum orP. imbricans, or among the six diploid species ofPolystichum from North America, including the circumborealP. lonchitis. The identity of rDNA repeats across all six North American species ofPolystichum may reflect an overall similarity of the nuclear genomes of these species, an observation supported by isozyme data as well. However, this nuclear similarity contrasts sharply with the highly divergent chloroplast genomes of these six species. The conservative nature of the rDNA inPolystichum also is in contrast to the much more variable rDNAs of most angiosperms investigated. Perhaps the tempo and mode of evolution of rDNA in ferns differ from those of angiosperms; however, the data base for fern rDNA is very small. Furthermore, the number of repeat types per individual is consistent with a diploid, rather than polyploid, condition despite the high chromosome number (n = 41) of these plants, although homogenization of multiple, divergent rRNA genes cannot be disproven.