A comparison of genome modifications leading to genetic and epigenetic tumorous transformation in Nicotiana spp. tissue cultures

Abstract

A single system is presented, where both genetic and epigenetic control of tumor induction can be studied at the same time. This system is offered by the amphidiploid tumorous hybrid Nicotiana gluuca X N . langsdo@i, a nontumorous mutant of it and the nontumorous parent species N . glauca and N . langsdofii. The aim of the present paper is to compare long-term in vitro cultures of tumorous (genetic and habituated), and nontumorous strains, through the characterization of their genomes according to several physico-chemical parameters. The data reported show that both qualitative and quantitative differences in DNA complexity are correlated with the tumorous transformation. Particularly, a high degree of mismatching between the DNAs of the tumorous and nontumorous hybrids and the lack, in the second genotype (nontumorous), of three DNA peaks in Agf-Cs2S04 analytical ultracentrifugation profile seem to support the hypothesis, suggested in a previous paper, of the presence, in the nontumorous mutant, of a gross chromosomal rearrangement, probably a deletion. Amplification and underreplication of specific sequences also seemed to be correlated with changes from the normal to the tumorous state, highly repetitive sequences being present in higher amounts in the normal strains and in the habituated N . glauca than in the case of the tumorous hybrid.Finally, DNA bound ion contents were found to be strikingly higher in tumorous than in nontumorous tissues. The results are discussed in the frame of the general hypothesis of high somatic genomic plasticity in plants.

A Physiological and Molecular Analysis of the GenusNicotiana

“…Moreover, as shown in Table 5, the species whose tissues give rise to faster growing callus on minimal media are clearly concentrated in Petunioides. It is worth noting that habituation is known to be an epigenetically induced character possibly related to changes in methylation levels in key genes (Bogani et al, 1995;Durante et al, 1986), which may become stably heritable as a monogenic allele as shown by Meins (1989) (Baroncelli et al, 1974). This hypothesis is also supported by data in FIG.…”

Identification of genes up-regulated in dedifferentiating Nicotania glauca pith tissue, using an improved method for constructing a subtractive cDNA library

“…Little is known about the identities of the genes involved in the early control of dedifferentiation. Since a high level of auxin is required to induce the formation of callus (1,13), it is likely that the expression of such genes, including possibly those coding for the mRNAs complementary to pNGSUB7 and pNGSUB8, is controlled at least in part by phytohormone levels. pNGSUB7 and pNGSUB8 appear to be derived from transcripts of two novel genes that are up-regulated early in dedifferentiation and to which we tentatively assign the names edeA and edeB respectively.…”

“…Plant growth and in vitro culture Pith tissue was isolated from greenhouse-grown N.glauca. Some of this tissue was frozen immediately in liquid nitrogen; the remainder was cultured as described previously (13) and harvested after 4 h or 8 h of culture. At various times of culture, part of the tissue was transferred into liquid LS medium containing actinomycin D (2) and maintained for a further two weeks to check the effectiveness of the drug treatment.…”