The Gibberellin Pathway Mediates KNOTTED1-Type Homeobox Function in Plants with Different Body Plans

Hay, Angela; Kaur, Hardip; Phillips, Andrew L.; Hedden, Peter; Hake, Sarah; Tsiantis, Miltos

doi:10.1016/s0960-9822(02)01125-9

Cited by 402 publications

(423 citation statements)

References 46 publications

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“…Furthermore, application of GA 3 or 1-NAA resulted in exclusion of all three KNOX proteins from the nucleus. It has been shown that KNOX gene expression in the SAM represses the activity of a GA biosynthetic enzyme, GA20-oxidase, implicating that increased GA production can occur in the leaf primordia where KNOX gene expression is down-regulated (Sakamoto et al, 2001;Hay et al, 2002Hay et al, , 2004. Therefore, our observation that GA 3 induces the nuclear exclusion of KNOX proteins fits well with our hypothesis that regulation of nuclear localization could represent a safety mechanism to ensure tight control of KNOX activity.…”

Section: Discussionsupporting

confidence: 90%

“…Transcription factors involved in SAM organization include the KNOX class-1 homeodomain proteins, which have been named after the maize protein KNOTTED1 (KN1) and are involved in maintenance of the undifferentiated state of stem cells Endrizzi et al, 1996;Brand et al, 2002). It has been proposed that the process of SAM maintenance depends on inhibition of gibberellin (GA) biosynthesis through down-regulation of GA20-oxidase by KNOX proteins (Kusaba et al, 1998;Sakamoto et al, 2001;Hay et al, 2002Hay et al, , 2004. In addition, interactions between KNOX genes and other plant hormones appear to be involved (Hamant et al, 2002;Scanlon, 2003;Hay et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

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Different subcellular localization and trafficking properties of KNOX class 1 homeodomain proteins from rice

et al. 2004

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Genes of the KN1-like homeobox (KNOX) class 1 encode transcription factors involved in shoot apical meristem development and maintenance. We studied the subcellular localization of Green Fluorescent Protein-tagged rice KNOX proteins (Oskn1-3) after particle bombardment of onion and rice cells and after transformation of Arabidopsis and rice with constitutive and inducible expression constructs. In all test systems, the three rice KNOX proteins showed nuclear and cytoplasmic localization patterns. However, Oskn1 additionally showed in some cells a distribution over punctae moving randomly in the cytosol. Use of an inducible expression system indicated a nuclear presence of Oskn1 in cells of the shoot apical meristem and post-transcriptional down-regulation in early leaf primordia. Arabidopsis and rice test systems were used to study effects of plant hormones and auxin transport inhibition on KNOX protein localization. Application of GA 3 or 1-NAA shifted protein localization completely to the cytoplasm and resulted in loss of the punctae formed by Oskn1. Conversely, NPA application induced a complete nuclear localization of the KNOX proteins. To study intercellular movement of the KNOX proteins we set up a novel co-bombardment assay in which trafficking of untagged KNOX proteins was visualized through the co-trafficking of green fluorescent or blue fluorescent marker proteins. In multiple independent experiments Oskn1 trafficked more extensively to neighboring cells than Oskn2 and Oskn3. Differences in the localization and trafficking properties of Oskn1, Oskn2 and Oskn3 correlate with differences in mRNA localization patterns and functional differences between the rice KNOX genes and their putative orthologues from other species.

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Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Different subcellular localization and trafficking properties of KNOX class 1 homeodomain proteins from rice

et al. 2004

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“…SAM regulators from the KNOTTED1-like homeobox (KNOXI) protein family were shown to induce expression of the cytokinin-biosynthesis gene ISOPENTENYL TRANSFERASE7 and accumulation of the hormone in the meristem (Jasinski et al, 2005;Yanai et al, 2005). Proteins from this family were also shown to negatively control GA level in the SAM by binding to the GA20ox promoter and directly repressing its transcription (Sakamoto et al, 2001;Hay et al, 2002;Chen et al, 2004). KNOXI and cytokinin both induced the expression of the gene encoding the GA-deactivating enzyme GA2ox at the base of the SAM, perhaps to block biologically active GAs transported to the SAM from flanking tissues (Jasinski et al, 2005).…”

Section: Reciprocal Interaction Between Ga and Cytokininmentioning

confidence: 99%

Mechanisms of Cross Talk between Gibberellin and Other Hormones

2007

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“…Cytokinins, which positively regulate cell division (RiouKhamlichi et al, 1999;Howell et al, 2003;Ferreira and Kieber, 2005), are required for meristem function and maintenance (Giulini et al, 2004;Leibfried et al, 2005;Kurakawa et al, 2007). GAs and auxin act antagonistically to cytokinins with GAs promoting cell differentiation (Chien and Sussex, 1996;Ogas et al, 1997;Perazza et al, 1998;Hay et al, 2002) and auxin promoting organ initiation (Reinhardt et al, 2000). Cytokinin signaling in plants is similar to the bacterial two-component phosphorelay system composed of a His kinase sensor and a response regulator.…”

mentioning

confidence: 99%

GeBP and GeBP-Like Proteins Are Noncanonical Leucine-Zipper Transcription Factors That Regulate Cytokinin Response in Arabidopsis

et al. 2007

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Understanding the role of transcription factors (TFs) is essential in reconstructing developmental regulatory networks. The plant-specific GeBP TF family of Arabidopsis thaliana (Arabidopsis) comprises 21 members, all of unknown function. A subset of four members, the founding member GeBP and GeBP-like proteins (GPL) 1, 2, and 3, shares a conserved C-terminal domain. Here we report that GeBP/GPL genes represent a newly defined class of leucine-zipper (Leu-zipper) TFs and that they play a redundant role in cytokinin hormone pathway regulation. Specifically, we demonstrate using yeast, in vitro, and split-yellow fluorescent protein in planta assays that GeBP/GPL proteins form homo-and heterodimers through a noncanonical Leu-zipper motif located in the C-terminal domain. A triple loss-of-function mutant of the three most closely related genes gebp gpl1 gpl2 shows a reduced sensitivity to exogenous cytokinins in a subset of cytokinin responses such as senescence and growth, whereas root inhibition is not affected. We find that transcript levels of type-A cytokinin response genes, which are involved in the negative feedback regulation of cytokinin signaling, are higher in the triple mutant. Using a GPL version that acts as a constitutive transcriptional activator, we show that the regulation of Arabidopsis response regulators (ARRs) is mediated by at least one additional, as yet unknown, repressor acting genetically downstream in the GeBP/GPL pathway. Our results indicate that GeBP/GPL genes encode a new class of unconventional Leu-zipper TF proteins and suggest that their role in the cytokinin pathway is to antagonize the negative feedback regulation on ARR genes to trigger the cytokinin response.

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The Gibberellin Pathway Mediates KNOTTED1-Type Homeobox Function in Plants with Different Body Plans

Abstract: We suggest that repression of GA activity by KNOX transcription factors is a key component of meristem function. Transfer of the KNOX/GA regulatory module from the meristem to the leaf may have contributed to the generation of the diverse leaf morphologies observed in higher plants.

Cited by 402 publications

References 46 publications

Different subcellular localization and trafficking properties of KNOX class 1 homeodomain proteins from rice

Different subcellular localization and trafficking properties of KNOX class 1 homeodomain proteins from rice

Mechanisms of Cross Talk between Gibberellin and Other Hormones

GeBP and GeBP-Like Proteins Are Noncanonical Leucine-Zipper Transcription Factors That Regulate Cytokinin Response in Arabidopsis

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