Initiation of auxin autonomy in Nicotiana glutinosa cells by the cytokinin-biosynthesis gene from Agrobacterium tumefaciens

Abstract

Agrobacteria carrying mutations at the auxin-biosynthesizing loci (iaaH and iaaM of the Ti plasmid) induce shoot-forming tumors on many plant species. In some cases, e.g. Nicotiana glutinosa L., tumors induced by such mutant strains exhibit an unorganized and fully autonomous phenotype. These characteristics are stable in culture at both the tissue and cellular level. We demonstrate that the cytokinin-biosynthesis gene (ipt) of the Ti plasmid is responsble for the induction of both auxin and cytokinin autonomy in N. glutinosa. Cloned cell lines carrying an ipt gene but lacking iaaH and iaaM are capable of accumulating indole-3-acetic acid. Interestingly, non-transformed N. glutinosa tissues exhibit an auxin-requiring phenotype when they are grown on medium supplemented with an exogenous supply of cytokinin. These results strongly indicate that exogenously supplied cytokinin does not mimic all the effects of the expression of the ipt gene in causing the auxin-autonomous growth of N. glutinosa cells.

Functional Analysis of the Tandem-Duplicated P450 Genes SPS/BUS/CYP79F1 and CYP79F2 in Glucosinolate Biosynthesis and Plant Development by Ds Transposition-Generated Double Mutants

“…These mutants also have elevated auxin levels (Reintanz et al, 2001;Tantikanjana et al, 2001), however, the proliferation of shoots observed in the sps/ cyp79F1 mutant is inconsistent with increased auxin levels, which is expected to produce the opposite effect. It has been shown that when cytokinin homeostasis is perturbed, the level of auxin can be affected (Binns et al, 1987;Makarova et al, 1996). Therefore we suggested that the phenotypic changes in sps/cyp79F1 mutants result primarily from increased cytokinin levels, and that the changes in auxin levels are a consequence of feedback mechanisms involved in hormone interactions (Tantikanjana et al, 2001).…”

“…Unlike the effect of auxin that results in decreased cytokinin levels, the effect of cytokinin on auxin levels is less well understood. Manipulation of cytokinin levels in plants by transformation with a bacterial cytokinin biosynthesis gene results in accumulation of increased levels of auxin (Binns et al, 1987;Makarova et al, 1996). Complex interactions are also observed between different glucosinolate biosynthetic pathways.…”

“…Therefore, the outcome appears to depend on the ratio of the two hormones (for review, see Tamas, 1995;Li and Bangerth, 1992). The two plant hormones not only play opposite roles in controlling plant growth and development, but also influence each other hormone homeostasis (Binns et al, 1987;Palni et al, 1988;Bangerth, 1994;Zhang et al, 1995;Makarova et al, 1996). We and others have described Arabidopsis mutants called supershoot (sps) or bushy (bus), which are disrupted in the gene encoding the cytochrome P450 CYP79F1 (Reintanz et al, 2001;Tantikanjana et al, 2001).…”

Cytokinin-to-Auxin Ratios and Morphology of Shoots and Tissues Transformed by a Chimeric Isopentenyl Transferase Gene

“…Since, in general, a corresponding increase in IAA levels was not observed, we speculate that cytokinin-producing cells may be providing a signal for inducing auxin-autonomous growth. Recently, Binns et al (2) have shown that N. glutinosa cells carrying the Ti ipt gene also exhibit auxin-autonomous growth.…”

“…However in some ofthese studies, the reported phytohormone concentrations may have been confounded by the presence of phytohormone-producing A. tumefaciens cells present within the galls (1). Also, possible effects of other T-DNA genes on the expression of plant phytohormone genes or on other plant cell processes cannot be excluded (2,14,18).…”