A novel cytokinin-resistant mutant of Arabidopsis with abbreviated shoot development

Deikman, Jill; Ulrich, Margaret

doi:10.1007/bf00202603

Cited by 59 publications

(27 citation statements)

References 40 publications

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“…Another apparent contradiction is the enhanced accumulation of anthocyanins in young rpn12a-1 seedlings. Because anthocyanin accumulation is augmented by exogenous cytokinins, a decrease in hormone sensitivity was expected to decrease anthocyanin accumulation, as was observed for the cyr1 mutant (Deikman and Ulrich, 1995). However, decreased cytokinin sensitivity combined with increased anthocyanin accumulation also has been observed in the fus6 mutant (Castle and Meinke, 1994).…”

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confidence: 89%

Cytokinin Growth Responses in Arabidopsis Involve the 26S Proteasome Subunit RPN12

et al. 2002

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The 26S proteasome is an ATP-dependent eukaryotic protease responsible for degrading many important cell regulators, especially those conjugated with multiple ubiquitins. Bound on both ends of the 20S core protease is a multisubunit regulatory particle that plays a crucial role in substrate selection by an as yet unknown mechanism(s). Here, we show that the RPN12 subunit of the Arabidopsis regulatory particle is involved in cytokinin responses. A T-DNA insertion mutant that affects RPN12a has a decreased rate of leaf formation, reduced root elongation, delayed skotomorphogenesis, and altered growth responses to exogenous cytokinins, suggesting that the mutant has decreased sensitivity to the hormone. The cytokinin-inducible genes CYCD3 and NIA1 are upregulated constitutively in rpn12a-1 , indicating that feedback-inhibitory mechanisms also may be altered. rpn12a-1 seedlings also showed changes in auxin-induced growth responses, further illustrating the close interaction between auxin and cytokinin regulation. In yeast, RPN12 is necessary for the G1/S and G2/M transitions of the cell cycle, phases that have been shown to be under cytokinin control in plants. We propose that RPN12a is part of the Arabidopsis 26S proteasome that controls the stability of one or more of the factors involved in cytokinin regulation. INTRODUCTIONRegulated protein turnover provides a mechanism to adjust rapidly to changing ligand concentrations and/or environmental conditions and is essential for many signal response pathways. In eukaryotes, the ubiquitin/26S proteasome pathway is particularly important, being responsible for removing most short-lived intracellular proteins (Hershko and Ciechanover, 1998;Callis and Vierstra, 2000). In this proteolytic pathway, proteins committed for degradation first are modified by the covalent attachment of multiple ubiquitins. This conjugation is directed by an ATP-dependent reaction cascade involving the sequential action of E1s, E2s, and E3s, which ultimately attach one or more ubiquitins to appropriate targets. In most cases, the ubiquitinated proteins then are recognized and degraded by the 26S proteasome, a multisubunit ATP-dependent protease with broad substrate specificity.The 26S proteasome is a 2-MD complex assembled from two particles: the 20S core particle (CP) and the 19S regulatory particle (RP) (Voges et al., 1999). The proteolytic activities reside within the central chamber of the 28-subunit CP, whereas the functions that direct substrate recognition, unfolding, and subsequent entry into the 20S particle reside within the Ͼ 18-subunit RP. The RP can be divided further in two subcomplexes, the lid and base (Glickman et al., 1998). The base contains six ATPase subunits, RPT1 to RPT6, which presumably use ATP hydrolysis to unfold target proteins, and three non-ATPase subunits, RPN1, RPN2, and RPN10. The lid contains nine additional RPN subunits (RPN3, RPN5 to RPN9, and RPN11 to RPN13). Many of the lid RPN subunits share sequence motifs with components of the COP9/signalosome and EIF3 co...

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confidence: 89%

Cytokinin Growth Responses in Arabidopsis Involve the 26S Proteasome Subunit RPN12

et al. 2002

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“…108, 1995 cytokinins have functions in nondividing tissue that are currently not understood and are underestimated. In this regard, it is interesting that an Arabidopsis mutant that is defective in its response to cytokinins in a root elongation assay does not produce anthocyanins in response to cytokinins (Deikman and Ulrich, 1995). The cyrl mutant has 10-fold less sensitivity to cytokinins in terms of root elongation and does not have decreased sensitivity to other plant hormones.…”

Section: Physiological Significance Of Cytokinin Control Of Anthocyanmentioning

confidence: 99%

Induction of Anthocyanin Accumulation by Cytokinins in Arabidopsis thaliana

Deikman¹,

Hammer²

1995

Plant Physiol.

242

154

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Arabidopsis thaliana plants treated with exogenous cytokinins accumulate anthocyanin pigments. We have characterized this response because it is potentially useful as a genetic marker for cytokinin responsiveness. Levels of mRNAs for four genes of the anthocyanin biosynthesis pathway, phenylalanine ammonia lyase 1 (PAL1 ), chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) were shown to increase coordinately in response to benzyladenine (BA). However, nuclear run-on transcription experiments suggested that although CHS and DFR are controlled by BA at the transcriptional level, PALl and CHI are controlled by BA posttranscriptionally. CHS mRNA levels increased within 2 h of BA spray application, and peaked by 3 h. Levels of PALl mRNA did not increase within 6 h of BA spray. We also showed that PAL1, CHS, CHI, and DFR mRNA levels fluctuate during a 24-h period and appear to be controlled by a circadian clock. The relation between cytokinin regulation and light regulation of CHS gene transcription is discussed.Cytokinins are important regulators of many aspects of plant development, including cell division, nutrient mobilization, senescence, chloroplast development, and apical dominance (Binns, 1994). Despite the widely acknowledged importance of cytokinin in plant development, very little is known about its mechanism of action at the molecular level.Cytokinins have been shown to affect the expression of specific genes by both increasing and decreasing the abundance of particular proteins or "As.A partia1 list of genes that are up-regulated by cytokinin includes nitrate reductase, rbcS, cab, hydroxypyruvate reductase in excised pumpkin cotyledons, a "multiple stimulus response" gene in Nicotiana plumbaginifolia cells, the early nodulin gene SrEnod2 from Sesbania rostrata, and a number of unidentified cDNAs from cultured soybean cells (Flores and Tobin, 1986;Chen, 1989;Crowell et al., 1990;Stabel et al., 1990;Dehio and de Bruijn, 1992;Dominov et al., 1992). Expression of phytochrome and a cucumber gene encoding a cDNA called CR9 are repressed by cytokinin (Cotton et al., 1990;Teramoto et al., 1994).

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“…Only a limited number of cytokinin response mutants have been isolated (Moffatt et al, 1991;Chaudhury et al, 1993;Deikman and Ulrich., 1995), and the genes corresponding to these mutant loci have yet to be identified. Putative cytokininbinding proteins have been purified (Brzobohaty et al, 1994), but the demonstration of their biological activity is still lacking.…”

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Posttranscriptional Regulation of the Sesbania rostrata Early Nodulin Gene SrEnod2 by Cytokinin

et al. 1996

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The mRNA from the Sesbania rosfrafa early nodulin gene SrEnod2 accumulates in response to cytokinin application. Nuclear run-on assays using isolated root nuclei have shown that this accumulation occurs posttranscriptionally, and northern blot analysis of nuclear and total RNA levels revealed that it occurs primarily in the cytoplasm and not in the nucleus. After cytokinin enhancement of SrFnod2 mRNA accumulation and the subsequent removal of cytokinin, the levels of SrEnod2 mRNA did not return to basal levels, but oscillated over a 36-h time course. Application of the translational inhibitor cycloheximide was found to inhibit the enhancement of SrEnod2 mRNA accumulation by cytokinin and to cause its rapid decay. Okadaic acid and staurosporine, inhibitors of protein phosphatases and kinases, respectively, also inhibited cytokinin enhancement of SrEnod2 mRNA accumulation. In addition, okadaic acid was found to cause a decrease in SrEnodZ mRNA levels. These results provide evidence for a posttranscriptional mechanism of cytokinin enhancement of SrFnod2 mRNA accumulation, which appears to require concurrent protein synthesis, to involve protein phosphatases and kinases, and to occur primarily in the cytoplasm of the plant cell.

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A novel cytokinin-resistant mutant of Arabidopsis with abbreviated shoot development

Cited by 59 publications

References 40 publications

Cytokinin Growth Responses in Arabidopsis Involve the 26S Proteasome Subunit RPN12

Cytokinin Growth Responses in Arabidopsis Involve the 26S Proteasome Subunit RPN12

Induction of Anthocyanin Accumulation by Cytokinins in Arabidopsis thaliana

Posttranscriptional Regulation of the Sesbania rostrata Early Nodulin Gene SrEnod2 by Cytokinin

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