Indole-3-acetic acid homeostasis in transgenic tobacco plants expressing the Agrobacterium rhizogenes rolB gene

Abstract

SummaryThe roll3 gene of the plant pathogen Agrobacterium rhizogenes has an important role in the establishment of hairy root disease in infected plant tissues. When expressed as a single gene in transgenic plants the RolB protein gives rise to effects indicative of increased auxin activity. It has been reported that the RolB product is a P-glucosidase and proposed that the physiological and developmental alterations in transgenic plants expressing the rolB gene are the result of this enzyme hydrolysing bound auxins, in particular (indole-3-acety1)-P-D-giucoside (IAGluc), and thereby bringing about an increase in the intracellular concentration of indole-3-acetic acid (IAA). Using tobacco plants as a test system, this proposal has been investigated in detail. The data obtained demonstrate that expression of the rolB encoded protein in transgenic tobacco does not produce a phenotype that resembles that of IAA overproducing plants, does not alter the size of the free IAA pool, has no significant effect on the rate of IAA metabolism, and, by implication, appears not to influence the overall rate of IAA biosynthesis. Furthermore, the in vivo hydrolysis of IAGluc, and that of the other IAA conjugates that were tested, is not affected. On the basis of these findings, it is concluded that the RolB phenotype is not the consequence of an increase

The influence of Agrobacterium rhizogenes on induction of hairy roots and ß-carboline alkaloids production in Tribulus terrestris L.

“…Previous findings have showed that the addition of IBA at optimum levels enhanced the growth of hairy root culture of Echinacea but had no effect on the production of secondary metabolites (Choffe et al 2000;Koroch et al 2002;Staniszewska et al 2003;Washida et al 2004). The TL-DNA rolB gene does not increase auxin levels (Nilsson et al 1993) but increases the sensitivity of plant cells to the growth regulator (Cardarelli et al 1987;Shen et al 1988;Spanó et al 1988;Maurel et al 1991;Welander et al 1998), probably by enhanced binding of the auxin to plant cell membranes (Filippini et al 1994), consequently increasing the rooting efficiency. The changes in sensitivity and content of endogenous growth regulators in plant cells undoubtedly affected the response effect of plant cells to exogenous growth regulators (He-Ping et al 2011).…”

Superroot, a recessive mutation in Arabidopsis, confers auxin overproduction.

“…Protoplasts derived from such tobacco plants are 105-fold more sensitive to auxin than protoplasts of wild-type plants . However, neither free nor conjugated IAA levels were modified in P35S-rolB-transformed tobacco plants or protoplasts (Nilsson et al, 1993;Schmülling et al, 1993;Delbarre et al, 1994). It is therefore unlikely that the surl mutant is affected in its ability to sense auxin.…”

Chemically induced expression of the rolC‐encoded β‐glucosidase in transgenic tobacco plants and analysis of cytokinin metabolism: rolC does not hydrolyze endogenous cytokinin glucosides in planta

“…Subsequent analyses have demonstrated that, unlike the original hypothesis suggested, rolB activity does not interfere with the endogenous auxin metabolism (Delbarre et al, 1994;Nilsson et al, 1993a;SchmLilling et al, 1993a). In a recent publication Fillipini et al (1996) reported that the rolB enzyme also has an in vitro tyrosine phosphatase activity.…”