Cytokinins and auxins control the expression of a gene in Nicotiana plumbaginifolia cells by feedback regulation.

Abstract

Both cytokinin (N6-benzyladenine [BA]) and auxin (2,4-dichlorophenoxyacetic acid [2,4-D]) stimulate the accumulation of an mRNA, represented by the cDNA pLS216, in Nicotiana plumbaginifolia suspension culture cells. The kinetics of RNA accumulation were different for the two hormones; however, the response to both was transient, and the magnitude of the response was dose dependent. Runoff transcription experiments demonstrated that the transient appearance of the RNA could be accounted for by feedback regulation of transcription and not by the induction of an RNA degradation system. The feedback mechanism appeared to desensitize the cells to further exposure of the hormone. In particular, cells became refractory to the subsequent addition of 2,4-D after the initial RNA accumulation response subsided. A very different response was observed when the second hormone was added to cells that had been desensitized to the first hormone. Under such conditions, BA produced a heightened response in cells desensitized to 2,4-D and vice versa. These findings support a model in which cytokinin further enhances the auxin response or prevents its feedback inhibition. The hormone-induced RNA accumulation was blocked by the protein kinase inhibitor staurosporin. On the other hand, the protein phosphatase inhibitor okadaic acid stimulated expression, and, in particular, okadaic acid was able to stimulate RNA accumulation in cells desensitized to auxin. This suggests that hormone activation involves phosphorylation of critical proteins on the hormone signaling pathway, whereas feedback inhibition may involve dephosphorylation of these proteins. The sequence of pLS216 is similar to genes in other plants that are stimulated by multiple agonists such as auxins, elicitors, and heavy metals, and to the gene encoding the stringent starvation protein in Escherichia coli. It is proposed that this gene family in various plants be called multiple stimulus response (msr) genes.

Light-induced expression of ipt from Agrobacterium tumefaciens results in cytokinin accumulation and osmotic stress symptoms in transgenic tobacco

“…All responses are also elicited by cytokinin treatment, albeit only in whole plants [38,39,40]. It appears that in the ice plant multiple stimuli trigger several stress-related responses, perhaps a general observation as similar results have been reported in tobacco for other inducible genes [13,25]. A comparison of plant gene expression, senescence and morphology during uninduced and induced cytokinin synthesis and salt stress may provide insights into the role of cytokinin in planta during various environmental and developmental processes.…”

“…At the physiological level, salt stress, ABA and cytokinin can affect the stomatal response [6]. Correlations between osmotic stress, cytokinins, and flowering have also been established before [25,13]. Thus, senescence and antisenescence activities exerted by cytokinins are not clearly separated and likely depend not only on the absolute cytokinin amount, but also the cytokinin ratio with respect to other growth regulators (e.g.…”

Molecular genetics of auxin and cytokinin

“…One of the best characterized examples of cytokinin regulated genes is the pLS216 gene from Nicotiana plumbaginifolia [32]. This gene is a member of a family of environmentally responsive genes, and therefore has been renamed msrl, for mutliple stimulus response.…”

“…These genes encode proteins related to the stringent starvation response protein from E. coli. Dominov et al [32] showed that the msrl mRNA accumulated in response to both cytokinin and auxin although the kinetics of accumulation differed for the two hormone treatments. The response to auxin peaked between 3-6 h, while the cytokinin response peaked in 24-48 h. In addition, cytokinin appeared to sensitize cells to subsequent auxin treatment.…”

Promoter analysis of the auxin-regulated tobacco glutathione S-transferase genes Nt103-1 and Nt103-35

“…Together with independently isolated homologous proteins from soybean [10,22], potato [62], Nicotiana plumbaginifolia [12], and maize [60] they are members of a hitherto unidentified new type of plant GSTs [13]. GSTs are a ubiquitous family of proteins that catalyze the nucleophilic addition of the thiol of reduced glutathione to a large variety ofhydrophobic electrophiles (for reviews see [9,11,43,51,55]).…”