Inverse Relationship between Polyamine Levels and the Degree of Phenotypic Alteration Induced by the Root-Inducing, Left-Hand Transferred DNA from Agrobacterium rhizogenes

Abstract

Floral induction in plants is a paradigm for signal perception, transduction, and physiological response. The introduction of root-inducing, left-hand transferred DNA (Ri T-DNA) into the genomes of several plants results in modifications of flowering (D Tepfer [1984] Cell 47: 959-967), including a delay in flowering in tobacco (Nicotiana tabacum). Conjugated polyamines are markers for flowering in numerous species of plants. In tobacco their accumulation is correlated with the onset of flowering (F Cabanne et al. [1981] Physiol Plant 53: 399-404). Using tobacco, we have explored the possibility of a correlation between the expression of Ri TL-DNA and changes in polyamine metabolism. We made use of two levels of phenotypic change, designated T and T', that retard flowering by 5 to 10 and 15 to 20 days, respectively. We show that delay in flowering is correlated with a reduction in polyamine accumulation and with a delay in appearance of conjugated polyamines, and we propose that genes carried by the Ri TL-DNA intervene either directly in polyamine metabolism or that polyamine metabolism is closely linked to direct effects of Ri T-DNA expression.

Attenuation of the Phenotype Caused by the Root-Inducing, Left-Hand, Transferred DNA and Its rolA Gene (Correlations with Changes in Polyamine Metabolism and DNA Methylation)

“…Here we examine four examples of attenuation of a transformed phenotype: the first two in plants containing wild-type Ri T-DNA, the third in plants transformed by the rolA gene controlled by the 35s promoter, and the fourth in transformants carrying the rolA gene under the control of the wild-type regulatory sequences. We extend previous studies showing that the degree of phenotypic change is correlated with the degree of alteration in PA metabolism (Martin-Tanguy et al, 1990), and we show that a flowering deficiency in plants expressing I',,,-rolA can be corrected by grafting onto rootstock that has been induced to flower. We also show that methylation is a correlate of spontaneous repression of the rolA gene under the control of the wild-type regulatory sequences, and we discuss evolutionary implications of these regulatory processes.…”

“…Increased sensitivity to auxin in tobacco pedicel explants containing wild-type TL-DNA was attributed to decreased sensitivity to ethylene (Smulders et al, 1991). The degree of phenotypic change associated with the wild-type Ri T-DNA was negatively correlated with the accumulation of PAs and their conjugates (Martin-Tanguy et al, 1990), and this transformed phenotype was mimicked by treating normal plants, not carrying foreign DNA, with a-difluoromethylornithine, an inhibitor of Orn decarboxylase, a key enzyme in PA metabolism (Burtin et al, 1991).…”

“…To be significant in evolution the Ri TL-DNA must get into gametes, explaining the fact that it encodes functions that stimulate organ formation (Tepfer, 1984(Tepfer, , 1989Levesque et al, 1988), in part by reducing the accumulation of PAs and their conjugates (Martin-Tanguy et al, 1990;Burtin et al, 1991). However, the physiological changes (e.g.…”

“…RNA was extracted (Verwoerd et al, 1989) and hybridization was performed after separation of RNAs in formaldehyde gels (Thomas, 1980). Amines were measured in shoot tops at different stages of floral development using previously described methods (Martin-Tanguy et al, 1978, 1990Cabanne et al, 1981). A shoot top was defined as the apical 1-to 1.5-cm fragment of the foliar stem before floral evocation.…”

“…the T' phenotype appeared in hemizygotes and the T phenotype appeared in homozygotes; thus, homozygosity attenuated the T' phenotype to the T phenotype. Selfing or outcrossing were used to produce uniform T and T' plants that served in the search for physiological correlates of these phenotypes (Martin-Tanguy et al, 1990). The N, T, and T' phenotypes are illustrated in Figure 1.…”