Light-induced expression of ipt from Agrobacterium tumefaciens results in cytokinin accumulation and osmotic stress symptoms in transgenic tobacco

Cytokinins are plant growth regulators that induce shoot formation, inhibit senescence and root growth. Experiments with hydroponically grown tobacco plants, however, indicated that exogenously applied cytokinin led to the accumulation of proline and osmotin. These responses were also associated with environmental stress reactions, such as salt stress, in many plant species. To test whether increased endogenous cytokinin accumulation led to NaCl stress symptoms, the gene ipt from Agrobacterium tumefaciens, encoding isopentenyl transferase, was transformed into Nicotiana tabacum cv. SR-1 under the control of the light-inducible rbcS-3A promoter from pea. In high light (300 mol PPFD m^-2 s^-1), ipt mRNA was detected and zeatin/zeatin glucoside levels were 10-fold higher than in control plants or when transformants were grown in low light (30 mol PPFD m^-2 s^-1). High light treatment was accompanied by increased levels of proline and osmotin when compared to low light grown transformed and untransformed control plants. Elevated in planta cytokinin levels induced responses also stimulated by salt stress, suggesting either common or overlapping signaling pathways are initiated independently by cytokinin and NaCl, setting in motion gene expression normally elicited by developmental processes such as flowering or environmental stress.Abbreviations IPT isopentenyl, transferase - rbcS-3A gene encoding a small subunit protein (SSU) of Rubisco from Pisum sativum - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase     

Analysis of randomly isolated cDNAs from developing endosperm of rice (Oryza sativa L.): evaluation of expressed sequence tags,and expression levels of mRNAs

Using a cDNA library prepared from poly(A)⁺ RNA from 10-day-old rice endosperm, partial nucleotide sequences of randomly isolated clones were analyzed. A total of 153 (30.6%) out of 500 cDNA clones showed high amino acid identity to previously identified genes. There was significant redundancy in cDNAs encoding prolamine and glutelin. About 21.0% of the cDNA clones were found to code for seed storage protein genes. Consequently, 37 independent genes were identified. Using cDNA clones encoding glutelin, prolamine, seed allergen, -1,4-glucan branching enzyme, glycine-rich RNA binding protein, metallothionein, non-specific lipid-transfer protein and ubiquitin conjugating enzyme the accumulation of mRNA during rice seed development was compared. Genes associated with seed storage protein and starch biosynthesis were expressed according to expected developmental stages. Glycinerich RNA binding protein genes as well as metallothionein-like protein genes were highly expressed in developing seeds, but low in leaves of whole plants.     

Inheritance of gusA and neo genes in transgenic rice

Inheritance of foreign genes neo and gusA in rice (Oryza sativa L. cv. IR54 and Radon) has been investigated in three different primary (T₀) transformants and their progeny plants. T₀ plants were obtained by co-transforming protoplasts from two different rice suspension cultures with the neomycin phosphotransferase II gene [neo or aph (3) II] and the -glucuronidase gene (uidA or gusA) residing on separate chimeric plasmid constructs. The suspension cultures were derived from callus of immature embryos of indica variety IR54 and japonica variety Radon. One transgenic line of Radon (AR2) contained neo driven by the CaMV 35S promoter and gusA driven by the rice actin promoter. A second Radon line (R3) contained neo driven by the CaMV 35S promoter and gusA driven by a promoter of the rice tungro bacilliform virus. The third transgenic line, IR54-1, contained neo driven by the CaMV 35S promoter and gusA driven by the CaMV 35S.Inheritance of the transgenes in progeny of the transgenic rice was investigated by Southern blot analysis and enzyme assays. Southern blot analysis of genomic DNA showed that, regardless of copy numbers of the transgenes in the plant genome and the fact that the two transgenes resided on two different plasmids before transformation, the introduced gusA and neo genes were stably transmitted from one generation to another and co-inherited together in transgenic rice progeny plants derived from self-pollination. Analysis of GUS and NPT II activities in T₁ to T₂ plants provided evidence that inheritance of the gusA and neo genes was in a Mendelian fashion in one plant line (AR2), and in an irregular fashion in the two other plant lines (R3 and IR54-1). Homozygous progeny plants expressing the gusA and neo genes were obtained in the T₂ generation of AR2, but the homozygous state was not found in the other two lines of transgenic rice.     

Molecular characterization and expression of a tobacco histone H1 cDNA

We have isolated a 1104 bp tobacco cDNA clone (H1c12) which includes an 846 bp open reading frame. This encodes a polypeptide of 282 amino acid residues and represents the largest plant H1 histone identified so far. The structure of the deduced protein shows the classical tripartite organization of the H1-type linker histones. The expression of the tobacco H1 histone gene(s) corresponding to the H1c12 cDNA clone was examined during different developmental stages. We found that, at the level of steadystate mRNA, expression of gene(s) encoding this H1 histone was rapidly induced in germinating seeds. The H1 gene was expressed in all tissues examined. However, its expression was higher in tissues known to contain meristematic cells. Furthermore, in the leaves of mature plants accumulation of the H1 mRNA exhibits a very characteristic oscillation. This latter finding indicates that, at least in fully developed plants, the expression of this type of H1 histone gene(s) is modulated by a diurnal cycle.     

Involvement of p21ras distinguishes positive and negative selection in thymocytes.

Small molecular weight GTP binding proteins of the ras family have been implicated in signal transduction from the T cell antigen receptor (TCR). To test the importance of p21ras in the control of thymocyte development, we generated mice expressing a dominant-negative p21ras protein (H-rasN17) in T lineage cells under the control of the lck proximal promoter. Proliferation of thymocytes from lck-H-rasN17 mice in response to TCR stimulation was nearly completely blocked, confirming the importance of p21ras in mediating TCR-derived signals in mature CD4+8- or CD8+4- thymocytes. In contrast, some TCR-derived signals proceeded unimpaired in the CD4+8+ thymocytes of mice expressing dominant-negative p21ras. Analysis of thymocyte development in mice made doubly transgenic for the H-Y-specific TCR and lck-H-rasN17 demonstrated that antigen-specific negative selection occurs normally in the presence of p21H-rasN17. Superantigen-induced negative selection in vivo also proceeded unhindered in H-rasN17 thymocytes. In contrast, positive selection of thymocytes in the H-Y mice was severely compromised by the presence of p21H-rasN17. These observations demonstrate that positive and negative selection, two conceptually antithetical consequences of TCR stimulation, are biochemically distinguishable.     

Phenylpropanoid defence responses in transgenic Lotus corniculatus: II. Modelling plant defence responses in transgenic root cultures using thiol and carbohydrate elicitors

Transformed root cultures of Lotus corniculatus L. cv. Leo weretreated with a range of thiol and carbohydrate elicitors. Boththiol reagents and fungal carbohydrate preparations resultedin an increase in the activity of phenylalanine ammonia lyase(PAL) in a concentration-dependent manner. One representativethiol elicitor, glutathione (GSH), and one fungal elicitor,derived from Rhynchosporium orthosporum autoclaved cell walls(Ro), were analysed in more detail. Both elicitors induced thetransient accumulation of vestitol, an isoflavan phytoalexin,in tissue and in culture medium. Treatment of Lotus root cultureswith the Ro elicitor resulted in a more rapid initial accumulationof this end product when compared with GSH, however, sativan(the 2–methoxy ester of vestitol) previously reportedto co-accumulate in Lotus leaves was only detected followingelicitation with high concentrations of GSH. Ro and GSH elicitorsalso induced the accumulation of a number of other phenylpropanoidcompounds putatively identified as chalcones. The addition ofthiol and carbohydrate elicitors to Lotus root cultures alsoresulted in characteristic changes in root morphology. Glutathione,in particular, resulted in the inhibition of root growth dueto differential damage of meristem cells. Key words: Lotus corniculatus, hairy roots, elicitors, phytoalexins.     

Structure and evolution of teleost mitochondrial control regions

We amplified and sequenced the mitochondrial control region from 23 species representing six families of teleost fish. The length of this segment is highly variable among even closely related species due to the presence of tandemly repeated sequences and large insertions. The position of the repetitive sequences suggests that they arise during replication both near the origin of replication and at the site of termination of the D-loop strand. Many of the conserved sequence blocks (CSBs) observed in mammals are also found among fish. In particular, the mammalian CSB-D is present in all of the fish species studied. Study of potential secondary structures of RNAs from the conserved regions provides little insight into the functional constraints on these regions. The variable structure of these control regions suggests that particular care should be taken to identify the most appropriate segment for studies of intraspecific variation. Correspondence to: T.D. Kocher     

Presence and abundance of CENP-B box sequences in great ape subsets of primate-specific α-satellite DNA

CENP-B, a highly conserved centromere-associated protein, binds to -satellite DNA, the centromeric satellite of primate chromosomes, at a 17-bp sequence, the CENP-B box. By fluorescence in situ hybridization (FISH) with an oligomer specific for the CENP-B box sequence, we have demonstrated the abundance of CENP-B boxes on all chromosomes (except the Y) of humans, chimpanzee, pygmy chimpanzee, gorilla, and orangutan. This sequence motif was not detected in the genomes of other primates, including gibbons, Old and New World monkeys, and prosimians. Our results indicate that the CENP-B box containing subtype of -satellite DNA may have emerged recently in the evolution of the large-bodied hominoids, after divergence of the phylogenetic lines leading to gibbons and apes; the box is thus on the order of 15–25 million years of age. The rapid process of dispersal and fixation of the CENP-B box sequence throughout the human and great ape genomes is thought to be a consequence of concerted evolution of -satellite subsets on both homologous and nonhomologous chromosomes.Correspondence to: T. Haaf