The OsTB1 gene, also known as FC1, encodes a protein which is a member of TCP gene family.The protein play a negative role in regulating tillering of rice.
Plant architecture is determined by the pattern of shoot branching . In most higher plants, shoot branches develop from axillary buds in the axils of leaves. Not all of the axillary buds develop, and each is subjected to a decision to continue growth or to become dormant, depending on a complex interplay between environmental and endogenous cues. Plant hormones are major players in the control of axillary bud growth. It has been known for a long time that two hormones in particular, auxin and cytokinin, are involved in this control. Auxin, which is supplied from the apical bud, indirectly suppresses axillary bud outgrowth, while cytokinins directly induce branching. During the past two decades, genetic and physiological analyses in pea and Arabidopsis have predicted the involvement of an additional, novel hormone in the control of shoot branching (for reviews, see . Recently it was demonstrated that the novel hormone, which inhibits bud outgrowth, is the group of compounds called strigolactones (SLs) or their downstream metabolites . Prior to the discovery of SLs as the branching hormone, more axillary growth1 (max1) to max4in Arabidopsis and five ramosus (rms) mutants in garden pea ( Pisum sativum) had been identifi ed as components of a novel graft-transmissible branching signal pathway .Consistent with results obtained from grafting experiments, max1 max3 and max4 were shown to be SL deficient, and their defects were rescued by the external application of an SL. On the other hand, a mutant of the MAX2 gene, which encodes an F-box leucine-rich repeat (LRR)-containing protein, was not rescued by the SL . MAX1 encodes CYP711A1, a class III cytochrome P450 . MAX3 and MAX4 encode carotenoid cleavage dioxygenases (CCDs) . The SL pathway seems to be well conserved across species . Molecular cloning showed that pea RMS1, RMS4and RMS5are orthologs of MAX4, MAX2 and MAX3, respectively . Analyses of branching mutants in rice indicated that the pathway is also conserved in monocot species. We reported on five tillering dwarf mutants of rice, dwarf3 (d3), d10, d14, d17 and d27. The high tillering dwarf1 (htd1) mutant, which resembles the five d mutants, was also described . After the molecular cloning, it turned out that D3and D10are orthologs of MAX2/RMS4and MAX4/RMS1, respectively , while HTD1 encodes an ortholog of MAX3/RMS5, and is the same locus as D17. Meanwhile, D14and D27were shown to be novel genes that work in the SL pathway . D27 encodes an iron-containing protein and is likely to be involved in SL biosynthesis . The d14mutant, also reported as d88and htd2, is insensitive to exogenous SL application and contains elevated SL levels . Although its molecular function has not yet been determined, it is postulated that D14also works in SL signaling . The mechanisms controlling cross-talk between the hormones are beginning to be elucidated. Recently it was revealed that one role of auxin is to suppress cytokinin biosynthesis in the stem . When the auxin supply from the apical bud is blocked, expression of isopentenyltransferase ( IPT) genes, which encode a rate-limiting enzyme of cytokinin biosynthesis, is rapidly up-regulated, and this results in the rapid synthesis of cytokinins in the stem. This cytokinin is transported to axillary buds and induces bud outgrowth. In addition, the auxin-dependent up-regulation of SL biosynthesis genes has been observed in all plant species analyzed so far . Although actual changes in SL levels have not yet been observed, a likely scenario is that the apically derived auxin induces SL biosynthesis, and the SLs act as second messengers to inhibit axillary bud outgrowth. Furthermore, SL biosynthesis is controlled by feedback regulation  and, at least in Arabidopsis, this feedback regulation is mostly dependent on auxin signaling. Together, these observations suggest that the growth of axillary buds is controlled by multiple independent and interacting pathways . Despite the remarkable progress in our understanding of the frameworks that control axillary bud outgrowth, little is known so far about how SLs act to control shoot branching. As a fi rst step towards understanding SL action at the molecular level, we report here that rice FINE CULM1 (FC1) partially works downstream of SLs to inhibit bud outgrowth. We propose that FC1serves as a hub gene where multiple signals are integrated to fi ne-tune the development of axillary buds.
The rice TB1 gene (OsTB1) was first identified based on its sequence similarity with maize TEOSINTE BRANCHED 1 (TB1) which is involved in lateral branching in maize. Both genes encode putative transcription factors carrying a basic helix-loop-helix type of DNA-binding motif, named the TCP domain. The deduced amino acid sequence of the OsTB1 ORF comprises 388 amino acid residues that is a member of the TCP family of transcription factors. Note that the in-frame stop codon was found two codons upstream of the deduced first methionine, suggesting that the methionine is used as an initiation codon. The DNA fragment also contains 1261-and 1198-bp 5 'and 3'-non-coding regions, respectively. The OsTB1 protein contains three significant sequence motifs, the SP, TCP and R domains. The R domain contains basic amino acid residues and is conserved in subpopulations of the TCP family. The SP domain contains a number of serine and proline residues, and is found in a limited number of members whose primary structures entirely match that of TB1. Although the precise molecular functions of these domains except for the TCP domain remain unknown, the close resemblance of the primary structures of OsTB1 and maize TB1 together with the entire sequences strongly suggests that the biological function of OsTB1 is similar to that of maize TB1. A series of genetic and reverse-genetic analyses thus conducted indicated that OsTB1 is a negative regulator for lateral branching in rice.
The OsMADS57 protein negatively regulates the expression of D14 functioning in strigolactone(SL) signalling to control tillering. This negative regulation by OsMADS57 is suppressed by interaction with OsTB1, leading to the balanced expression of D14 for tillering.
The expression of OsTB1 was detected in vegetative apical meristems, young roots and tillers of rice, and it seemed that there was weak expression in developed spikelets, but no expression in young leaves. The expression of OsTB1in tillers was stronger than in other tissues.
The total number of tillers is significantly reduced by the overexpression of OsTB1, but increased in an fc1 mutant containing a loss-of-function mutation of OsTB1. This strongly suggests that OsTB1 functions as a negative regulator for lateral branching in rice.An fc1 mutant strain, M56, exhibited a bushy morphology as to enhanced lateral branching. Quantitative analysis showed that the fc1 mutant generated a threefold higher number of tillers than the wild-type strain did.Sequencing analysis of the PCR amplified OsTB1 ORF from the fc1 genome revealed one nucleotide deletion in OsTB1. The C-base at the 327th nucleotide in the ORF was deleted in the fc1 mutant, resulting in a frame shift of the ORF generating a stop codon just downstream of the mutation.
The OsTB1 shows 70%, 41%, 32% and 31% similarity with TB1, CYC, PCF1 and PCF2, respectively. The conserved TCP region of OsTB1 has 93%, 80%,49% and 46% similarity with TB1, CYC,PCF1 and PCF2,respectively. Moreover , the R conserved regions among TB1,CYC, OsTB1 are nearly identical.
Strigolactones (SLs) are a group of newly identified plant hormones that control plant shoot branching. SL signaling requires the hormone-dependent interaction of DWARF14 (D14) which is regulated by the interaction of OsMADS57 with OsTB1. In this study, they have identified theD53gene that encodes a substrate of the SCF(D3) ubiquitination complex, and revealed that D53 functions as a repressor ofSL signalling. These results allow to establish a model of SL signalling that is centred around a D14–D3–D53 signalling axis . In the presence of SLs, perception of SL by D14 and the SCF(D3) complex leads to ubiquitination of D53 and its subsequent degradation by the ubiquitin proteasome system, which in turn releases the repression of downstream target genes . In the d53 plant, the mutated D53 protein is resistant to ubiquitination and degradation, leading to the accumulation of d53, which blocks SL signalling and results in dwarf and high tillering phenotypes. The signalling paradigm of SLs is still emerging as SLs are a relatively new class of plant hormone for which many knowledge gaps still exist. Identification ofD53 as a repressor of SL signalling adds a critical piece of information that helps to paint the whole picture of the SL signalling pathways. Moreover, the work has also provided an important paradigm for understanding signalling pathways of other plant hormones, for example, karrikins, a class of plant growth regulators found in the smoke of burning plants. Karrikin signalling involves MAX2 and KAI2, a D14-like a/b-hydrolase. It is probable that a similar protein to D53 could serve as the repressor of karrikin signalling. Indeed, multiple D53-like proteins are found in rice and inArabidopsis. We propose that these proteins could serve as repressors of signalling by karrikin and other plant hormones, in a similar way to D53 in SL signalling.
Labs working on this gene
- National Laboratory of Plant Molecular Genetics,Institute of Plant Physiology and Ecology,Chinese Academy of Sciences, China
- The Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, China
- Graduate School of Agriculture and Life Sciences, University of Tokyo, Tokyo 113-8657 ,Japan
- Bioscience Center, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
- McSteen , P. and Leyser , O. ( 2005 ) Shoot branching . Annu. Rev. Plant Biol. 56 : 353 – 374 .
- Beveridge , C.A. ( 2006 ) Axillary bud outgrowth: sending a message . Curr. Opin. Plant Biol. 9 : 35 – 40 .
- Ongaro , V. and Leyser , O. ( 2008 ) Hormonal control of shoot branching . J. Exp. Bot. 59 : 67 – 74 .
- Gomez-Roldan , V. , Fermas , S. , Brewer , P.B. , Puech-Pagès , V. , Dun , E.A. , Pillot , J.P. , et al . ( 2008 ) Strigolactone inhibition of shoot branching . Nature 455 : 189 – 194 .
- Umehara , M. , Hanada , A. , Yoshida , S. , Akiyama , K. , Arite , T. , Takeda-Kamiya , N. , et al . ( 2008 ) Inhibition of shoot branching by new terpenoid plant hormones . Nature 455 : 195 – 200 .
- Stirnberg , P. , van de Sande , K. and Leyser , H.M.O. ( 2002 ) MAX1 and MAX2control shoot lateral branching in Arabidopsis . Development 129 : 1131 – 1141 .
- Sorefan , K. , Booker , J. , Haurogne , K. , Goussot , M. , Bainbridge , K. , Foo , E. , et al . ( 2003 ) MAX4and RMS1are orthologous dioxygenase-like genes that regulate shoot branching in Arabidopsis and pea . Genes Dev. 17 : 1469 – 1474 .
- Booker , J. , Sieberer , T. , Wright , W. , Williamson , L. , Willett , B. , Stirnberg , P. , et al . ( 2005 ) MAX1encodes a cytochrome P450 family member that acts downstream of MAX3/4 to produce a carotenoidderived branch-inhibiting hormone . Dev. Cell 8 : 443 – 449 .
- Booker , J. , Auldridge , M. , Wills , S. , McCarty , D. , Klee , H. and Leyser , O. ( 2004 ) MAX3/CCD7 is a carotenoid cleavage dioxygenase required for the synthesis of a novel plant signaling molecule . Curr. Biol. 1 4 : 1232 – 1238 .
- Beveridge , C.A. and Kyozuka , J. ( 2010 ) New genes in the strigolactonerelated shoot branching pathway . Curr. Opin. Plant Biol. 13 : 34 – 39 .
- Foo , E. , Bullier , E. , Goussot , M. , Foucher , F. , Rameau , C. and Beveridge , C.A. ( 2005 ) The branching gene RAMOSUS1mediates interactions among two novel signals and auxin in pea . Plant Cell 17 : 464 – 474 .
- Jhonson , X. , Brcich , T. , Dun , E.A. , Goussot , M. , Haurogné , K. , Beveridge , C.A. , et al . ( 2006 ) Branching genes are conserved across species. Genes controlling a novel signal in pea are coregulated by other long-distance signals . Plant Physiol. 142 : 1014 – 1026 .
- Beveridge , C.A. , Dun , E.A. and Rameau , C. ( 2009 ) Pea has its tendril in branching discoveries spanning a century from auxin to strigolactones . Plant Physiol. 151 : 985 – 990 .
- Ishikawa , S. , Maekawa , M. , Arite , T. , Onishi , K. , Takamure , I. and Kyozuka , J. ( 2005 ) Suppression of tiller bud activity in tillering dwarf mutants of rice . Plant Cell Physiol. 46 : 79 – 86 .
- Zou , J. , Zhang , S. , Zhang , W. , Li , G. , Chen , Z. , Zhai , W. , et al . ( 2006 ) The rice HIGH-TILLERING DWARF1encoding an ortholog of Arabidopsis MAX3is required for negative regulation of the outgrowth of axillary buds . Plant J. 48 : 687 – 698 .
- Arite , T. , Iwata , H. , Ohshima , K. , Maekawa , M. , Nakajima , M. , Kojima , M. , et al . ( 2007 ) DWARF10, an RMS1/MAX4/DAD1ortholog, controls lateral bud outgrowth in rice . Plant J. 51 : 1019 – 1029 .
- Arite , T. , Umehara , M. , Ishikawa , S. , Hanada , A. , Maekawa , M. , et al . ( 2009 ) d14, a strigolactone-insensitive mutant of rice, shows an accelerated outgrowth of tillers . Plant Cell Physiol. 5 0 : 1416 – 1424 .
- Lin , H. , Wang , R. , Qian , Q. , Yan , M , Meng , X. , Fu , Z. , et al . ( 2009 ) DWARF27, an iron-containing protein required for the biosynthesis of strigolactones, regulates rice tiller bud outgrowth . Plant Cell 2 1 : 1512 – 1525 .
- Gao , Z. , Qian , Q. , Liu , X. , Yan , M. , Feng , Q. and Dong , G. , ( 2009 ) Dwarf 88, a novel putative esterase gene affecting architecture of rice plant . Plant Mol. Biol. 71 : 265 – 276 .
- Liu , W. , Wu , C. , Fu , Y. , Hu , G. , Si , H. , Li , Z. , et al . ( 2009 ) Identifi cation and characterization of HTD2: a novel gene negatively regulating tiller bud outgrowth in rice . Planta 230 : 649 – 658 .
- Tanaka , M. , Takei , K. , Kojima , M. , Sakakibara , H. and Mori , H. ( 2006 ) Auxin controls local cytokinin biosynthesis in the nodal stem in apical dominance . Plant J. 45 : 1028 – 36 .
- Shimizu-Sato , T. , Tanaka , M. and Mori , H. ( 2009 ) Auxin–cytokinin interactions in the control of shoot branching . Plant Mol. Biol. 6 9 : 429 – 435 .
- Heyward , A. , Stirnberg , P. , Beveridge , C. and Leyser , O. ( 2009 ) Interaction between auxin and strigolactone in shoot branching control . Plant Physiol. 151 : 400 – 412 .
- Dun E.A. , Hanan , J. and Beveridge , C. ( 2009 ) Computational modeling and molecular physiology experiments reveal new insight into shoot branching in pea . Plant Cell 21 : 3459 – 3472 .
- Takeda T, Suwa Y, Suzuki M, et al. The OsTB1 gene negatively regulates lateral branching in rice[J]. The Plant Journal 2003; 33(3): 513-20
- Guo S, Xu Y, Liu H, et al. The interaction between OsMADS57 and OsTB1 modulates rice tillering via DWARF14[J]. Nature communications 2013; 4: 1566.
- Minakuchi K, Kameoka H, Yasuno N, et al. FINE CULM1 (FC1) works downstream of strigolactones to inhibit the outgrowth of axillary buds in rice[J]. Plant and cell physiology 2010; 51(7): 1127-35.
- Hu W, Zhang S, Zhao Z, Sun C, Zhao Y, Luo D. The Analysis of the Structure and Expression of OsTBl Gene in rice[J]. Journal of plant physiology and molecular biology 2002; 29(6): 507-14.
- Jiang L, Liu X, Xiong G, et al. DWARF 53 acts as a repressor of strigolactone signalling in rice[J]. Nature 2013.