A Novel Class of Gibberellin 2-Oxidases Control Semidwarfism, 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: 9.34). 11/2008; 20(10):2603-18. DOI: 10.1105/tpc.108.060913
Source: PubMed


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.

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Available from: Yue-ie Hsing, Mar 16, 2014
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    • "In other species such as citrus and pea, GA-defective mutants produce more lateral branches than WT plants (Fagoaga et al., 2007; de Saint Germain et al., 2013). On the other hand, dwarf transgenic plants that overexpress the catabolic enzymes GA2ox, in rice (Lo et al., 2008), Paspalum notatum Flugge (Agharkar et al., 2007), and aspen (Mauriat et al., 2011), have also been found to produce more lateral branches than WT plants. "
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    ABSTRACT: Gibberellins (GAs) are phytohormones that regulate a wide range of developmental processes in plants. Levels of active GAs are regulated by biosynthetic and catabolic enzymes like the GA 2-oxidases (GA2oxs). In tomato (Solanum lycopersicum L.) C19 GA2oxs are encoded by a small multigenic family of five members with some degree of redundancy. In order to investigate their roles in tomato, the silencing of all five genes in transgenic plants was induced. A significant increase in active GA4 content was found in the ovaries of transgenic plants. In addition, the transgenic unfertilized ovaries were much bigger than wild-type ovaries (about 30 times) and a certain proportion (5-37%) were able to develop parthenocarpically. Among the GA2ox family, genes GA2ox1 and -2 seem to be the most relevant for this phenotype since their expression was induced in unfertilized ovaries and repressed in developing fruits, inversely correlating with ovary growth. Interestingly, transgenic lines exhibited a significant inhibition of branching and a higher content of active GA4 in axillary buds. This phenotype was reverted, in transgenic plants, by the application of paclobutrazol, a GA biosynthesis inhibitor, suggesting a role for GAs as repressors of branching. In summary, this work demonstrates that GA 2-oxidases regulate gibberellin levels in ovaries and axillary buds of tomato plants and their silencing is responsible for parthenocarpic fruit growth and branching inhibition. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.
    Journal of Experimental Botany 06/2015; DOI:10.1093/jxb/erv300 · 5.53 Impact Factor
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    • "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. "
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    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; 17(6). DOI:10.1111/plb.12358 · 2.63 Impact Factor
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    • "interacts with two other well-studied phytohormones, CK and SL, in the control of lateral bud outgrowth in J. curcas. Although a negative correlation between gibberellin levels and branching or tillering has been observed in some species, such as Arabidopsis (Silverstone et al. 1997), pea (Scott et al. 1967, Luisi et al. 2011), rice (Lo et al. 2008, Qi et al. 2011), barley (Jia et al. 2009, Jia et al. 2011), turfgrass (Agharkar et al. 2007) and Populus trees (Mauriat et al. 2011, Zawaski and Busov 2014), we found that gibberellin acts as a positive regulator in the regulation of shoot branching in the perennial woody plant J. curcas, demonstrated by direct GA 3 treatment (Fig. 1) and by overexpressing the gibberellin biosynthesis gene JcGA20ox1 (Supplementary Fig. S1). On the basis of the results of this study, we hypothesize that gibberellin may function as a potent promoter of shoot branching in many perennial woody plants. "
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    ABSTRACT: Strigolactone (SL), auxin, and cytokinin (CK) interact to regulate shoot branching. CK has long been considered to be the only key phytohormone to promote lateral bud outgrowth. Here we report that gibberellin (GA) also acts as a positive regulator in the control of shoot branching in the woody plant Jatropha curcas. We show that GA and CK synergistically promote lateral bud outgrowth, and that both hormones influence the expression of putative branching regulators, J. curcas BRANCHED1 and BRANCHED2, which are key transcription factors maintaining bud dormancy. Moreover, treatment with paclobutrazol, an inhibitor of de novo GA biosynthesis, significantly reduced the promotion of bud outgrowth by CK, suggesting that GA is required for CK-mediated axillary bud outgrowth. In addition, SL, a plant hormone involved in the repression of shoot branching, acted antagonistically to both GA and CK in the control of lateral bud outgrowth. Consistent with this, the expression of JcMAX2, a J. curcas homolog of Arabidopsis MORE AXILLARY GROWTH 2 encoding an F-box protein in the SL signaling pathway, was repressed by GA and CK treatment. We also provide physiological evidences that GA also induces shoot branching in many other trees, such as papaya, indicating a more complicated regulating network occurs in the control of shoot branching in some perennial woody plants. © The Author(s) 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.
    Plant and Cell Physiology 06/2015; 56(8). DOI:10.1093/pcp/pcv089 · 4.93 Impact Factor
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