Isolation of mRNA species related to the rooting induction in almond and apple through the differential display technique

Differential display of mRNA has been recently developed as a tool to detect and characterize changes in gene expression. We applied this technique to fruit trees plantlets induced to root in vitro, in order to isolate and study genes involved in root induction. A reproducible pattern of polymerase chain reaction (PCR) products was obtained, both in almond and apple, in vertical polyacrylamide gels stained with ethidium bromide. Differences in PCR fingerprinting were detected in mRNAs of basal part of either auxin induced or non induced microcuttings. Thus, we suggest that this technique can be used in woody species to detect changes among mRNA populations during root induction. This revised version was published online in July 2006 with corrections to the Cover Date.     

A duplex retina and the electroretinogram in the nocturnal Perodicticus potto.

The presence of cones in potto's retina has been proved beyond doubt although they are very restricted in number (1 cone for 300 rods). Morphologically, speaking there is no point in calling these cones "rudimentary" except for their slender outer segment. There are red sensitive elements in that retina at wavelengths beyond the spectral sensitivity of visual purple and it is tempting to assume that these elements are cones. The ERG evoked from these elements by red light differs from that in response to white and blue light. They dark-adapt faster than the receptors sensitive to blue and white flashes. However in some of their properties, for example fusion frequency, these cones behave like rods in other species. As these few cones seem to activate the bipolar cells nearly as effectively as the numerous rods, it is suggested that these cones may be responsible for day vision in the potto.     

Insights into the regenerative property of plant cells and their receptivity to transgenesis: Wheat as a research case study

From a holistic perspective, the discovery of cellular plasticity, a very interesting property of totipotency, underlies many topical issues in biology with important medical applications, while transgenesis is a core research tool in biology. Partially known, some basic mechanisms involved in the regenerative property of cells and in their receptivity to transgenesis are common to plant and animal cells and highlight the principle of the unity of life. Transgenesis provides an important investigative instrument in plant physiology and is regarded as a valuable tool for crop improvement. The economic, social, cultural and scientific importance of cereals has led to a rich stream of research into their genetics, biology and evolution. Sustained efforts to achieve the results obtained in the fields of genetic engineering and applied biotechnology reflect this deep interest. Difficulties encountered in creating genetically modified cereals, especially wheat, highlighted the central notions of tissue culture regeneration and transformation competencies. From the perspective of combining or encountering these competencies in the same cell lineage, this reputedly recalcitrant species provides a stimulating biological system in which to explore the physiological and genetic complexity of both competencies. The former involves two phases, dedifferentiation and redifferentiation. Cells undergo development switches regulated by extrinsic and intrinsic factors. The re-entry into the cell division cycle progressively culminates in the development of organized structures. This is achieved by global chromatin reorganization associated with the reprogramming of the gene expression pattern. The latter is linked with surveillance mechanisms and DNA repair, aimed at maintaining genome integrity before cells move into mitosis, and with those mechanisms aimed at genome expression control and regulation. In order to clarify the biological basis of these two physiological properties and their interconnectedness, we look at both competencies at the core of defense/adaptive mechanisms and survival, between undifferentiated cell proliferation and organization, constituting a transition phase between two different dynamic regimes, a typical feature of critical dynamic systems. Opting for a candidate-gene strategy, several gene families could be proposed as relevant targets for investigating this hypothesis at the molecular level.     

Analysis of expression profiles of selected genes associated with the regenerative property and the receptivity to gene transfer during somatic embryogenesis in Triticum aestivum L.

The physiological, biochemical and molecular mechanisms regulating the initiation of a regenerative pathway remain partially unknown. Efforts to identify the biological features that confer transformation ability, or the tendency of some cells to induce transgene silencing, would help to improve plant genetic engineering. The objective of our study was to monitor the evolution of plant cell competencies in relation to both in vitro tissue culture regeneration and the genetic transformation properties. We used a simple wheat regeneration procedure as an experimental model for studying the regenerative capacity of plant cells and their receptivity to direct gene transfer over the successive steps of the regenerative pathway. Target gene profiling studies and biochemical assays were conducted to follow some of the mechanisms triggered during the somatic-to-embryogenic transition (i.e. dedifferentiation, cell division activation, redifferentiation) and affecting the accessibility of plant cells to receive and stably express the exogenous DNA introduced by bombardment. Our results seem to indicate that the control of cell-cycle (S-phase) and host defense strategies can be crucial determinants of genetic transformation efficiency. The results from studies conducted at macro-, micro- and molecular scales are then integrated into a holistic approach that addresses the question of tissue culture and transgenesis competencies more broadly. Through this multilevel analysis we try to establish functional links between both regenerative capacity and transformation receptiveness, and thereby to provide a more global and integrated vision of both processes, at the core of defense/adaptive mechanisms and survival, between undifferentiated cell proliferation and organization.     

Expression of a chimeric GUS gene construct as a tool to study nodule morphogenesis in chicory leaves

Leaves from micropropagated chicory plantlets were cultivated in vitro to regenerate organogenic nodules. The nodules were transformed with a 2.3 kb fragment of an apple calmodulin promoter region fused to the coding sequence of uidA reporter gene. Histochemical detection of β-glucuronidase expression in transgenic regenerants showed that vessel-associated cells were strongly stained. Previous histological investigations have shown that the differentiation of vascular elements is essential to nodule and bud-derived-nodule development. Therefore, β-glucuronidase activity was tested in a single transgenic chicory line during nodule morphogenesis and bud regeneration. The vascular connections between leaves and nodules, then between nodules and buds were stained blue, indicating an alternative system for determining the histological origin of nodules and adventitious buds from chicory leaf explants. This revised version was published online in June 2006 with corrections to the Cover Date.