D. De Waele

Transfection and transformation of Agrobacterium tumefaciens

SummaryThe freeze thaw transfection procedure of Dityatkin et al. (1972) was adapted for the transfection and transformation of A. tumefaciens. Transfection of the strains B6S3 and B6-6 with DNA of the temperate phage PS8cc186 yielded a maximum frequency of 2 10-7 transfectants per total recipient population. In transformation of the strain GV3100 with the P type plasmid RP4 a maximum frequency of 3.5 10-7 transformants per total recipient population was obtained. Agrobacterium Ti-plasmids were introduced in the strain GV3100 with a maximal efficiency of 4.5 10-8. These experiments provide further evidence that the Ti-plasmid is responsible for the oncogenic properties of A tumefaciens and for its capacity to induce “opine” synthesis in Crown-gall plant cells.

Epigenetics: A Challenge for Genetics, Evolution, and Development?

Abstract: In this paper, it is argued that differences in how one relates the genome to its surrounding contexts leads to diverse interpretations of the term epigenetics. Three different approaches are considered, ranging from gene‐centrism, over gene‐regulation, to dynamic systems approaches. Although epigenetics receives its widest interpretation in a systems approach, a paradigmatic shift has taken place in biology from the abandonment of a gene‐centric position on to the present. The epistemological and ontological consequences of this shift are made explicit.

Theories in early embryology: close connections between epigenesis, preformationism, and self-organization.

Abstract: In current biological and philosophical literature, the use of the terms epigenesis and epigenetics has increased tremendously. As these terms are often confused, this paper aims at clarifying the distinction between them by drawing their conceptual and historical evolutions. The evolution of the term epigenesis is situated in the context of early embryological studies. Departing from Aristotles natural philosophy, it is shown that epigenesis gained alternating attention from the 17th century onwards, as it was introduced into neo‐classical embryology and considered to be the opposite of the preformationist tradition. Where preformation stated that the germ cells of each organism contain preformed miniature adults that unfold during development, epigenesis held that the embryo forms by successive gradual exchanges in an amorphous zygote. Although both traditions tried to explain developmental organization, religious and metaphysical arguments on the conception of embryonic matter as either active or passive determined the scope of their respective explanations. It is shown that these very arguments still underlie the use of gene‐centric metaphors in the molecular revolution of the 20th century.

Agrobacterium Tumefaciens: What Segment of the Plasmid is Responsible for the Induction of Crown Gall Tumors ?

Several causes of plant tumors have been described (1). Particularly intriguing is the case of the crown gall tumors. The agent inducing this disease is a Gram-negative bacterium, Agrobacterium tumefaciens belonging to the family of the Rhizobiaceae. Until now it is the only documented case where an oncogenic agent is of bacterial origin.

Interactions between the oomycete Pythium arrhenomanes and the rice root-knot nematode Meloidogyne graminicola in aerobic Asian rice varieties

BackgroundAerobic rice fields are frequently infested by pathogenic oomycetes (Pythium spp.) and the rice root-knot nematode Meloidogyne graminicola. Here, the interaction between Pythium arrhenomanes and Meloidogyne graminicola was studied in rice roots of two aerobic rice varieties. In different experimental set-ups and infection regimes, plant growth, rice yield, Pythium colonization, as well as establishment, development and reproduction of M. graminicola were studied.ResultsIn this study, it is shown that the presence of P. arrhenomanes delays the establishment, development and reproduction of M. graminicola compared to single nematode infected plants. The delay in establishment and development of M. graminicola becomes stronger with higher P. arrhenomanes infection pressure.ConclusionsOur data indicate that P. arrhenomanes antagonizes M. graminicola in the rice root and that the plant benefits from this antagonism as shown by the yield data, especially when either of the pathogens is present in high levels.

Host response of rice genotypes from crosses of high-yielding and drought-tolerant Oryza sativa advanced breeding lines to the rice root-knot nematode Meloidogyne graminicola

Abstract The host response to Meloidogyne graminicola infection of 30 advanced breeding lines developed from crosses between high-yielding and drought-tolerant Oryza sativa genotypes was evaluated in outdoor raised beds. None of the advanced breeding lines showed resistance to M. graminicola comparable to the M. graminicola-resistant African rice (O. glaberrima) genotype TOG5674. However, rice genotype IR86815-23-4-1-2 was identified tolerant which showed no yield reduction even when infected with M. graminicola. IR82635-B-B-143-1, IR85733-19-4-1-1, IR85733-19-4-2-4, IR85,735-42-1-4-1 and IR 85735-42-1-4-4 were less sensitive to M. graminicola infection with less than 20% yield reduction compared to other rice genotypes. These rice genotypes could alleviate yield losses in M. graminicola-infested rice fields in regions with limited resources to control M. graminicola and when resistant cultivars are not available.