Os03g0203200

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HTD2gene could negatively regulate tiller bud outgrowth by the strigolactone pathway HTD2 gene could negatively regulate tiller bud outgrowth by the strigolactone pathway

Annotated Information

Function

The function of Dwarf 88 was confirmed by complementation test and antisense analysis. D88, thus, represents a new category of genes that regulates cell growth and organ development and consequently plant architecture. The potential relationship between the tiller formation associated genes and D88 is discussed and future identification of the substrate for D88 may lead to the characterization of new pathways regulating plant development .

We propose that D14 functions downstream of strigolactone synthesis, as a component of hormone signaling or as an enzyme that participates in the conversion of strigolactones to the bioactive form . The d14 mutant exhibits increased shoot branching with reduced plant height like the previously characterized strigolactone-defi cient and -insensitive mutants d10 and d3 , respectively .

The results suggest that the HTD2 gene could negatively regulate tiller bud outgrowth by the strigolactone pathway . which is characterized by a high tillering and dwarf phenotype. Phenotypic analysis of the mutant showed that the mutation did not aVect formation of tiller bud, but promoted the subsequent outgrowth of tiller bud .

基因信息

HTD2，亦称D88 或D14，编码一个酯酶，抑制水稻分枝发生，负调节水稻分蘖数。D14 可能是独角金内酯（Strigolactones, SLs）信号途径的一个组分，在其下游起作用。中国的2个小组和日本的1个小组在同一年报道了对该基因的克隆。 分蘖数由内源和外源信号分子所调节的分蘖芽的形成及随后向外生长所决定。htd2 是从15000个转基因株系中分离出的一个水稻突变体，该突变体分蘖数增多且矮化。表型分析表明HTD2 的突变不影响分蘖芽的形成，但促进了随后分蘖芽的向外生长。通过图位克隆的方法并设计17个新的插入/缺失分子标记来分离HTD2 基因，利用F2 和F3 群体构建了HTD2 基因附近的高分辨率物理图谱，该基因位于BAC克隆OSJNBa0009J13上，最终定位在相距12.8kb的DNA标记HT41和HT52之间。对突变体12.8kb的目标区域进行克隆和测序发现T-DNA的插入导致一个酯酶/脂肪酶/硫酯酶家族基因的启动子和第一个外显子之间相距463bp的片段缺失。另外，该基因表达受抑制的转基因植株出现分蘖增多和矮化的表型。因此，这个酯酶/脂肪酶/硫酯酶家族基因即为HTD2 基因（Liu et al., 2009）。 Link = [1]|

基因克隆与生物学功能分析

HTD2 cDNA全长1487bp，包含有2 个外显子，编码一个由318 氨基酸组成的蛋白产物。T-DNA的插入导致HTD2 的启动子和第一个外显子之间相距463bp的片段缺失（Liu et al., 2009）

Expression

Semidwarf VS. normaltype rice plants at ripening (from reference ).

The gene Dwarf 88 was expressed in most rice organs, with especially high levels in the vascular tissues . The mutant had excessive shorter tillers and smaller panicles and seeds compared to the wild-type. A reduction in number and size of parenchyma cells around stem marrow cavity as well as a delay in the elongation of parenchyma cells caused slender tillers and dwarfism in the d88 mutant .

The d14 branching phenotype could not be rescued by exogenous strigolactones. In addition, the d14 mutant contained a higher level of 2 ′ - epi -5-deoxystrigol than the wild type. Positional cloning revealed that D14 encodes a protein of the α / β -fold hydrolase superfamily, some members of which play a role in metabolism or signaling of plant hormones .

Leaves, inflorescences, internodes, nodes, roots and lateral buds (about 2 cm in length) were excised from 100-day-old wild-type plants. The mRNA expression of HTD2 in different tissues was analyzed by real-time PCR (Fig.6). The results showed that the highest expression levels were observed in leaves, followed by internodes, nodes, roots,lateral buds and inXorescences. The HTD2 expression levels in leaves were signiWcantly higher than that in other tissues .

Evolution

Semidwarf VS. normaltype rice plants at ripening (from reference ).

The strigolactone signal regulates bud outgrowth by controlling auxin transport capacity in the stem in Arabidopsis .In max mutants, there is an increase in auxin transport capacity. The elevated capacity of auxin transport causes bud outgrowth,since increased expression of PIN auxin eZux carrier was observed in maxmutants and the pin1mutation suppressed the max phenotype. In htd2 mutant, the biosynthesis of strigolactone is likely to be arrested as a result of the htd2 mutation. The absence of strigolactone could result in increased auxin transport, further promoting bud outgrowth in the htd2 mutant. Four high tillering and dwarf genes, including D10,HTD1, D3and TB1, have been cloned in rice .Their orthologous genes have similar functions in Arabidopsis, pea and petunia .These findings indicate that monocot and eudicot plants share a conserved mechanism controlling shoot branching. In the present study, we identified a new high tillering and dwarf gene HTD2, which encodes an esterase/lipase/thioesterase. Although orthologous genes for HTD2 widely exist in other plants (Fig.Phylogenetic tree of HTD2 and its homologous proteins), none has been characterized so far. Characterization of the HTD2gene and study on its interaction with other tillering-related genes will be helpful to further understand the regulation mechanism of outgrowth of tiller buds in plants..

Knowledge Extension

A proposed model of Strigolactone(SL) signalling patyway ).

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 of D53 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 α / β-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 Center for Gene Research/Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 500 Caobao Road, 200233 Shanghai, China
• State Key Laboratory of Rice Biology, China National Rice Research Institute, Chinese Academy of Agricultural Sciences, 310006 Hangzhou, China
• Ishikawa Prefectural University, Nonoichi, Ishikawa, 921-8836 Japan
• RIKEN Plant Science Center, Tsurumi, Yokohama, 230-0045 Japan
• Graduate School of Agriculture and Life Sciences, University of Tokyo, Yayoi, Bunkyo, Tokyo, 113-8657 Japan
• Research Institute for Bioresources, Okayama University, Kurashiki, Okayama, 710-0046 Japan
• State Key Laboratory of Rice Biology, China National Rice Research Institute, 359 Tiyuchang Road, 310006 Hangzhou, Zhejiang, China
• Biotechnology Research Center, China Three Gorges University, 443002 Yichang, Hubei, China

Structured Information

Gene Name	AK070827
Description	1487 bp mRNA linear PLN 04-DEC-2008.
Version	AK070827.1 GI:32980850
Length	1487 bp bp
Definition	Oryza sativa Japonica Group cDNA clone:J023064N24, full insert sequence.
Source	Oryza sativa Japonica Group (Japanese rice) ORGANISM Oryza sativa Japonica Group Eukaryota; Viridiplantae; Streptophyta; Embryophyta; Tracheophyta; Spermatophyta; Magnoliophyta; Liliopsida; Poales; Poaceae; BEP clade; Ehrhartoideae; Oryzeae; Oryza.
Chromosome	Chromosome 2
Location	Chromosome 3:203..1159
Sequence Coding Region	203..1159
Expression	GEO Profiles:AK070827
Genome Context	{{{GCID}}}
Gene Structure	{{{GSID}}}
Coding Sequence	{{{CDNA}}}
Protein Sequence	<aaseq>MLRSTHPPPSSPSSSSSGGGGGGGSSASSSSEKTMVGGGGGGGG GSGSAAPSGAKLLQILNVRVVGSGERVVVLSHGFGTDQSAWSRVLPYLTRDHRVVLYD LVCAGSVNPDHFDFRRYDNLDAYVDDLLAILDALRIPRCAFVGHSVSAMIGILASIRR PDLFAKLVLIGASPRFLNDSDYHGGFELEEIQQVFDAMGANYSAWATGYAPLAVGADV PAAVQEFSRTLFNMRPDISLHVCQTVFKTDLRGVLGMVRAPCVVVQTTRDVSVPASVA AYLKAHLGGRTTVEFLQTEGHLPHLSAPSLLAQVLRRALARY</aaseq>
Gene Sequence	<dnaseqindica>1..61#121..181#241..301#361..421# 481..541#601..661#721..781#841..901#961..1021#1081..1141#1201..1261#1321..1381#1441# gacaaaaatc ccaatctacc accgcaccca acgaagctta agacagtgga ataaagcaga gagagaaatc aaagcaagaa agagagagaa gaagcgaggc aagagtcaag accatctccc atggccagtg gtgatagtag tagtagtagt agtatataaa aggggagcgc gccacggctt gccaatccgc cgcgctggtg tgatgctgcg atcgacgcat ccgccgccca gtagcccgag cagcagcagc agcggcggcg gcgggggcgg ggggtcgtcg gcgtcgtcga gctcggagaa gacgatggtg ggcggcgggg gaggaggggg aggagggagc gggtcggcgg cgccgagcgg ggcgaagctg ctgcagatcc tgaacgtgcg ggtggtgggg agcggcgagc gggtggtggt gctgtcgcat ggcttcggga cggaccagtc ggcgtggagc cgcgtgctgc cgtacctcac ccgcgaccac cgcgtcgtgc tctacgacct cgtctgcgcc ggcagcgtca acccggacca cttcgacttc cgccgctacg acaacctcga cgcctacgtc gacgacctgc tcgccatcct cgacgcgctc cgcatcccgc gctgcgcctt cgtcggccac tccgtctccg ccatgatcgg catcctcgcc tccatccgac gacctgacct cttcgccaag cttgtcctca tcggcgcctc tccccggttc ttgaacgaca gcgactacca cggcgggttc gagctggagg agatacagca ggtgttcgac gcgatggggg cgaactactc ggcgtgggcg acggggtacg cgcctctggc ggtgggcgcc gacgtgccgg cggcggtgca ggagttcagc cgcaccctct tcaacatgcg cccggacatc tccctccacg tctgccagac cgtcttcaag accgacctcc gcggcgtgct cggcatggtc cgcgccccct gcgtcgtcgt ccagaccacc cgcgacgtct ccgtcccggc ctccgtcgcc gcctacctca aggcccacct cggcggccgc accaccgtcg agttcctcca gaccgagggt cacctccccc acctcagcgc ccccagcctc ctcgcccagg tgctccgccg cgctctcgcc cggtactaat ccaacgcccc ccgcacgcca ccgcggcgcg ccgcgcgtgc gcgtagccgc agcgacgagt caaaacgaag gagaaaaaaa aaaaccaccg cagctgcggc tacggtacgt gtggcccagt agggggacac gcatccctct actgtttttt ttttttttac cgcgtcggat tttactgcat ttttaccctc ctcttctcag gcctagaaaa tatttcggcg cgacctgcca agaccgagag tgtactgtag cattagtgct cgatttttac ctaccttact ctattggaaa aaaaattaca ttactggagt gcttcgtgca tacaatt</dnaseqindica>
External Link(s)	NCBI Gene:AK070827, [2]