Leaf Senescence Is Delayed in Tobacco Plants Expressing the Maize Homeobox Gene knotted1 under the Control of a Senescence-Activated Promoter

Ori, Naomi; Juarez, Michelle T.; Jackson, David A.; Yamaguchi, Judy; Banowetz, Gary M.; Hake, Sarah

doi:10.2307/3870799

Cited by 80 publications

(113 citation statements)

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“…Third, the KNAT2-GR plants grown in the presence DEX exhibited an inhibition of hypocotyl elongation and epinastic cotyledons, much like the KNAT2-GR plant grown in the presence of BAP (Cary et al, 1995;personal observations). Fourth, the KNAT2-GR activation led to a delay in leaf senescence, a phenotype induced by both cytokinins and overexpression of KN1 in tobacco and KNAT1 in lettuce (Gan and Amasino, 1995;Ori et al, 1999;Frugis et al, 2001). Finally, preliminary differential screening indicated common targets between cytokinin and KNAT2 (O. Hamant, F. Nogré, J. Traas, and V. Pautot, unpublished data).…”

Section: Discussionmentioning

confidence: 93%

The KNAT2 Homeodomain Protein Interacts with Ethylene and Cytokinin Signaling

Hamant¹,

Nogué

Belles‐Boix³

et al. 2002

Plant Physiology

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Using a transgenic line that overexpresses a fusion of the KNAT2 (KNOTTED-like Arabidopsis) homeodomain protein and the hormone-binding domain of the glucocorticoid receptor (GR), we have investigated the possible relations between KNAT2 and various hormones. Upon activation of the KNAT2-GR fusion, we observed a delayed senescence of the leaves and a higher rate of shoot initiation, two processes that are also induced by cytokinins and inhibited by ethylene. Furthermore, the activation of the KNAT2-GR fusion induced lobing of the leaves. This feature was partially suppressed by treatment with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, or by the constitutive ethylene response ctr1 mutation. Conversely, some phenotypic traits of the ctr1 mutant were suppressed by the activation of the KNAT2-GR fusion. These data suggest that KNAT2 acts synergistically with cytokinins and antagonistically with ethylene. In the shoot apical meristem, the KNAT2 gene is expressed in the L3 layer and the rib zone. 1-Aminocyclopropane-1-carboxylic acid treatment restricted the KNAT2 expression domain in the shoot apical meristem and reduced the number of cells in the L3. The latter effect was suppressed by the activation of the KNAT2-GR construct. Conversely, the KNAT2 gene expression domain was enlarged in the ethylene-resistant etr1-1 mutant or in response to cytokinin treatment. These data suggest that ethylene and cytokinins act antagonistically in the meristem via KNAT2 to regulate the meristem activity.Plant organs are formed continuously during postembryonic development from groups of indeterminate meristematic cells. In Angiosperms like Arabidopsis, the cells within the shoot apical meristem (SAM) are distributed in three layers: L1, L2, and L3 (Clark, 1997; Barton, 1998). The cells derived from the L1 will preferentially form the epidermis, whereas L2 and L3 layers will give rise to the inner parts of the organs. The SAM is furthermore organized in three distinct zones: the peripheral zone, the central zone, and the rib zone. The central zone maintains a population of founder cells. Cells are recruited to the peripheral zone and the rib zone from the central zone, and generate the lateral organs and the inner parts of the stem, respectively. The family of KNOX (KNOTTED homeobox) genes plays a crucial role in the SAM: in Arabidopsis, the KNAT (KNOTTED-like in Arabidopsis) family comprises eight members (Serikawa et al., 1996;Reiser et al., 2000;Semiarti et al., 2001). Of these, four have been associated with meristem function. The best characterized is the STM (SHOOTMERISTEMLESS) gene, which is absolutely required for meristem maintenance (Long et al., 1996). More recently, loss-of-function mutants have been described for KNAT1 (Douglas et al., 2002;Venglat et al., 2002). The molecular characterization of the bp (brevipedicellus) mutant of Arabidopsis has revealed that BP encodes the KNAT1 protein. In addition to its role in meristem maintenance in redundancy with STM, BP plays a key role in regulating the inf...

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Section: Discussionmentioning

confidence: 93%

The KNAT2 Homeodomain Protein Interacts with Ethylene and Cytokinin Signaling

Hamant¹,

Nogué

Belles‐Boix³

et al. 2002

Plant Physiology

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“…KNOX overexpressing tobacco leaves display a delay in senescence similar to that seen in plants with increased cytokinin levels (Kusaba et al, 1998). Expressing KN1 under the control of the senescence-associated gene promoter in tobacco leads to increased levels of cytokinin and a delay in leaf senescence, suggesting that KN1 acts to increase cytokinin levels (Ori et al, 1999). In tobacco, ectopic KNOX gene expression directly down-regulates the gibberellic acid biosynthesis gene, GA20 oxidase, through binding of target sites in the promoter and first intron (Sakamoto et al, 2001).…”

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confidence: 79%

L1 Division and Differentiation Patterns Influence Shoot Apical Meristem Maintenance

2006

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Plant development requires regulation of both cell division and differentiation. The class 1 KNOTTED1-like homeobox (KNOX) genes such as knotted1 (kn1) in maize (Zea mays) and SHOOTMERISTEMLESS in Arabidopsis (Arabidopsis thaliana) play a role in maintaining shoot apical meristem indeterminacy, and their misexpression is sufficient to induce cell division and meristem formation. KNOX overexpression experiments have shown that these genes interact with the cytokinin, auxin, and gibberellin pathways. The L1 layer has been shown to be necessary for the maintenance of indeterminacy in the underlying meristem layers. This work explores the possibility that the L1 affects meristem function by disrupting hormone transport pathways. The semidominant Extra cell layers1 (Xcl1) mutation in maize leads to the production of multiple epidermal layers by overproduction of a normal gene product. Meristem size is reduced in mutant plants and more cells are incorporated into the incipient leaf primordium. Thus, Xcl1 may provide a link between L1 division patterns, hormonal pathways, and meristem maintenance. We used double mutants between Xcl1 and dominant KNOX mutants and showed that Xcl1 suppresses the Kn1 phenotype but has a synergistic interaction with gnarley1 and rough sheath1, possibly correlated with changes in gibberellin and auxin signaling. In addition, double mutants between Xcl1 and crinkly4 had defects in shoot meristem maintenance. Thus, proper L1 development is essential for meristem function, and XCL1 may act to coordinate hormonal effects with KNOX gene function at the shoot apex.

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“…Known coordinating factors of cell proliferation and differentiation in the SAM are transmembrane receptor proteins (e.g., CLV1) and transcription factors of the homeodomain class (e.g., WUS, STM, KNAT1), which interact in regulatory loops (19). Recent data indicate that a reciprocal interaction between cytokinins and some of these transcription factors exists (20)(21)(22). A role for cytokinins in the regulation of SAM differentiation could be realized through local gradients of the hormone or differences in the distribution of different cytokinin metabolites.…”

Section: Discussionmentioning

confidence: 99%

Regulation of plant growth by cytokinin

Werner

Motyka

Strnad

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

916

703

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Cytokinins are a class of plant-specific hormones that play a central role during the cell cycle and influence numerous developmental programs. Because of the lack of biosynthetic and signaling mutants, the regulatory roles of cytokinins are not well understood. We genetically engineered cytokinin oxidase expression in transgenic tobacco plants to reduce their endogenous cytokinin content. Cytokinin-deficient plants developed stunted shoots with smaller apical meristems. The plastochrone was prolonged, and leaf cell production was only 3-4% that of wild type, indicating an absolute requirement of cytokinins for leaf growth. In contrast, root meristems of transgenic plants were enlarged and gave rise to faster growing and more branched roots. These results suggest that cytokinins are an important regulatory factor of plant meristem activity and morphogenesis, with opposing roles in shoots and roots.

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Leaf Senescence Is Delayed in Tobacco Plants Expressing the Maize Homeobox Gene knotted1 under the Control of a Senescence-Activated Promoter

Cited by 80 publications

References 0 publications

The KNAT2 Homeodomain Protein Interacts with Ethylene and Cytokinin Signaling

The KNAT2 Homeodomain Protein Interacts with Ethylene and Cytokinin Signaling

L1 Division and Differentiation Patterns Influence Shoot Apical Meristem Maintenance

Regulation of plant growth by cytokinin

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