Article

A novel class of gibberellin 2-oxidases control semidwarfing, tillering and root development in rice

Institute of Molecular Biology, National Chung-Hsing University, Taichung 402, Taiwan, Republic of China.
The Plant Cell (Impact Factor: 9.58). 11/2008; 20(10):2603-18. DOI: 10.1105/tpc.108.060913
Source: PubMed

ABSTRACT Gibberellin 2-oxidases (GA2oxs) regulate plant growth by inactivating endogenous bioactive gibberellins (GAs). Two classes of GA2oxs inactivate GAs through 2beta-hydroxylation: a larger class of C(19) GA2oxs and a smaller class of C(20) GA2oxs. In this study, we show that members of the rice (Oryza sativa) GA2ox family are differentially regulated and act in concert or individually to control GA levels during flowering, tillering, and seed germination. Using mutant and transgenic analysis, C(20) GA2oxs were shown to play pleiotropic roles regulating rice growth and architecture. In particular, rice overexpressing these GA2oxs exhibited early and increased tillering and adventitious root growth. GA negatively regulated expression of two transcription factors, O. sativa homeobox 1 and TEOSINTE BRANCHED1, which control meristem initiation and axillary bud outgrowth, respectively, and that in turn inhibited tillering. One of three conserved motifs unique to the C(20) GA2oxs (motif III) was found to be important for activity of these GA2oxs. Moreover, C(20) GA2oxs were found to cause less severe GA-defective phenotypes than C(19) GA2oxs. Our studies demonstrate that improvements in plant architecture, such as semidwarfism, increased root systems and higher tiller numbers, could be induced by overexpression of wild-type or modified C(20) GA2oxs.

Download full-text

Full-text

Available from: Yue-ie Hsing, Mar 16, 2014
0 Followers
 · 
338 Views
  • Source
    • "The GAs are well known for their role in several aspects of plant development and reproductive phase change; however, their role in shoot branching has hardly been characterised (Rameau et al. 2015). In Arabidopsis, rice, pea and sunflower GA-deficient mutants showed increase in branching proliferation with respect to the wild type (WT; Murfet & Reid 1993; Silverstone et al. 1997; Lo et al. 2008; Fambrini et al. 2011). Nevertheless, recessive mutants characterised by defects in repressors of GA signalling (i.e. "
    [Show abstract] [Hide abstract]
    ABSTRACT: GRAS proteins belong to a plant transcriptional regulator family that function in the regulation of plant growth and development. Despite their important roles, in sunflower, only one GRAS gene (HaDella1), with the DELLA domain, has been reported. Here, we provide a functional characterization of a GRAS-like gene from Helianthus annuus (Ha-GRASL), lacking the DELLA motif. The Ha-GRASL gene contains an intronless open reading frame of 1,743 bp encoding 580 amino acids. Conserved motifs in the GRAS domain are detected, including VHIID, PFYRE, SAW, and two LHR motifs. Within the VHII motif, the P-H-N-D-Q-L residues are entirely maintained. Phylogenetic analysis reveals that Ha-GRASL belongs to the SCARECROW LIKE4/7 (SCL4/7) subfamily of the GRAS consensus tree. Accumulation of Ha-GRASL mRNA at the adaxial boundaries from P6/P7 leaf primordia, suggests a role of Ha-GRASL in the initiation of median and basal axillary meristems (AMs) of sunflower. When Ha-GRASL is overexpressed in Arabidopsis WT plants, the number of lateral bolts increases differently from untransformed plants. However, Ha-GRASL slightly affects the lateral suppressor (las-4-) mutation. Therefore, we hypothesize that Ha-GRASL and LAS are not functionally equivalent. The overexpression of Ha-GRASL reduces metabolic flow of gibberellins (GAs) in Arabidopsis and this modification could be relevant in AM development. Phylogenetic analysis includes LAS and SCL4/7 in the same major clade suggesting a more recent separation of these genes with respect to other GRAS members. We propose that some features of their ancestor, as well as AM initiation and outgrowth, are partially retained in both LAS and SCL4/7. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Plant Biology 06/2015; DOI:10.1111/plb.12358 · 2.41 Impact Factor
  • Source
    • "Conversely, recessive DELLA protein mutants such as the tomato procera mutant (Bassel et al., 2008) – DELLA proteins are main repressors of GA signaling – exhibited reduced shoot branching and/or altered branching patterns. Overexpressing GA catabolism genes to reduce GA levels produced increased branching phenotypes (Agharkar et al., 2007; Lo et al., 2008). In pea, GAand SL-deficient double mutants displayed stronger branching than single mutants, suggesting that GAs act independently of SLs to repress branching (de Saint Germain et al., 2013b). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Shoot branching patterns result from the spatio-temporal regulation of axillary bud outgrowth. Numerous endogenous, developmental and environmental factors are integrated at the bud and plant levels to determine numbers of growing shoots. Multiple pathways that converge to common integrators are most probably involved. We propose several pathways involving not only the classical hormones auxin, cytokinins and strigolactones, but also other signals with a strong influence on shoot branching such as gibberellins, sugars or molecular actors of plant phase transition. We also deal with recent findings about the molecular mechanisms and the pathway involved in the response to shade as an example of an environmental signal controlling branching. We propose the TCP transcription factor TB1/BRC1 and the polar auxin transport stream in the stem as possible integrators of these pathways. We finally discuss how modeling can help to represent this highly dynamic system by articulating knowledges and hypothesis and calculating the phenotype properties they imply.
    Frontiers in Plant Science 01/2015; volume 5. DOI:10.3389/fpls.2014.00741 · 3.95 Impact Factor
  • Source
    • "However, the relationship between CKX enzymes and crown root formation is unknown. Activation tagging is quite a powerful tool for functional genomics studies and has been successfully used to identify a number of gain-of-function mutants in rice (Lo et al., 2008; Zhang et al., 2009; Wu et al., 2011; Zhao et al., 2013). For example, a dominant mutant, ili1-D, with increased lamina joint inclination and hypersensitivity to brassinosteroid, was identified by a screening of rice transfer DNA (T-DNA) activation-tagging lines (Zhang et al., 2009). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Crown roots constitute the majority of the rice root system, and play an important role in rice growth and development. However, the molecular mechanism of crown root formation in rice is still not well understood. Here, we characterized a rice dominant mutant, root enhancer1 (ren1-D), which was observed to exhibit a more robust root system, increased crown root number, and reduced plant height. Molecular and genetic analyses revealed that these phenotypes are caused by the activation of a cytokinin oxidase/dehydrogenase (CKX) family gene, OsCKX4. Subcellular localization demonstrated that OsCKX4 is a cytosolic isoform of CKX. OsCKX4 is predominantly expressed in leaf blades and roots, and it is the dominant CKX preferentially expressed in the shoot base where crown root primordia are produced, underlining its role in root initiation. OsCKX4 is induced by exogenous auxin and cytokinin in the roots. Furthermore, one-hybrid assays revealed that OsCKX4 is a direct binding target of both auxin response factor OsARF25 and the cytokinin response regulators ORR2 and ORR3. Overexpression and RNAi of OsCKX4 confirmed that OsCKX4 plays a positive role in crown root formation. Moreover, expression analysis revealed a significant alteration in the expression of auxin-related genes in the ren1-D mutants, indicating that the OsCKX4 mediates crown root development by integrating the interaction between cytokinin and auxin. Transgenic plants harboring OsCKX4 under the control of a root-specific promoter RCc3 displayed enhanced root development without affecting their shoot parts, suggesting that this strategy could be a powerful tool in rice root engineering.
    Plant physiology 05/2014; 165:1035-1046. DOI:10.1104/pp.114.238584 · 7.39 Impact Factor
Show more