青海育成小麦5个主效矮秆基因的分子检测

为系统了解青海小麦矮秆基因的分布特点,并进一步为青海高原小麦的株高育种提供优异种质资源。本研究利用5个矮秆基因的特异性分子标记对82份青海小麦品种资源中的矮秆基因进行了检测,并对不同矮秆基因的降秆效应进行了分析。结果表明:82份青海育成小麦品种中有49份材料至少含有一个矮秆基因,其中Rht-B1b的分布频率最高,约占参试材料的28.0%,其次是分布频率为23.2%的Rht8基因,而矮秆基因Rht-D1b、Rht5以及Rht12的分布频率分别为9.8%、13.4%、9.8%。在49份含有不同种类矮秆基因的材料中,其中16份材料同时含有2种及以上的矮秆基因,即RhtB1b和Rht8、Rht-D1b和Rht8、Rht-B1b和Rht5、Rht-D1b和Rht5、Rht8和Rht5、Rht-B1b和Rht12、Rht5和Rht12,并未发现同时含有矮秆基因Rht-B1b和Rht-D1b的品种;2份材料分别含有3种矮秆基因,即Rht-B1b、Rht8、Rht12和Rht-B1b、Rht5、Rht8;其余31份材料仅含有1种矮秆基因。82份青海育成小麦材料中仅含有Rht-B1b的材料11份,平均株高为86.2 cm,其降秆效应为5.7%;只含有Rht-D1b的材料有5份,平均株高为84.9 cm,其降秆效应为7.1%;仅含有Rht8的材料有9份,平均株高为88.6 cm,其降秆效应为3.1%。因此,在青海育成小麦品种中,矮秆基因的降秆效应为Rht-D1bRht-B1bRht8。     

矮秆基因对小麦部分农艺性状的效应

以中国主要麦区的124份小麦品种为材料,利用分子标记和系谱分析相结合,对其按照所含的矮秆基因Rht-B1b、Rht-D1b和Rht8进行分类,结合田间株高、旗叶长、小穗数和穗粒数以及室内苗期根系长度等农艺形状的调查,分析不同矮秆基因对小麦农艺性状的效应.结果显示:(1)参试的124份小麦品种(系)中23份含有Rht-B1b,7份含有Rht-D1b,22份含有Rht8基因,34份同时含有Rht-B1b和Rht8,16份同时含有Rht-D1b和Rht8,可分为6组.(2)Rht-B1b和Rht-D1b在降低株高的同时也缩短了旗叶的长度和苗期叶长,Rht8对株高的影响较弱,对旗叶和苗期叶长的影响也较小;3个矮秆基因对苗期根系长度、小穗数没有显著影响;Rht-D1b和Rht8显著增加穗粒数.研究表明,矮秆基因Rht8对小麦株高以及其他农艺性状的影响均较小,但能够显著增加穗粒数,是小麦矮化育种中比较理想的矮秆基因.     

Effects of dwarfing genes on the genetic background of wheat varieties in southern Ukraine

The effects of the Rht8c, Rht-B1b, Rht-B1e, and Rht-D1b genes on wheat height have been investigated. Variations in these effects are significantly modified by the genetic background and year conditions. A combination of the Rht8c, Rht-B1a, Rht-D1b, and Ppd-D1a alleles is the most advantageous for the conditions of southern Ukraine, since it is associated with optimal plant height under contrasting conditions within different years. The genotypes of some varieties were shown to include gene(s) that were unidentifiable by the molecular markers and significantly decreased plant height.     

Influence of the gibberellin-sensitive Rht8 dwarfing gene on leaf epidermal cell dimensions and early vigour in wheat (Triticum aestivum L.)

BACKGROUND AND AIMS: The gibberellin-insensitive Rht-B1b and Rht-D1b dwarfing genes are known to reduce the size of cells in culms, leaves and coleoptiles of wheat. Resulting leaf area development of gibberellin-insensitive wheats is poor compared to standard height (Rht-B1a and Rht-D1a) genotypes. Alternative dwarfing genes to Rht-B1b and Rht-D1b are available that reduce plant height, such as the gibberellin-responsive Rht8 gene. This study aims to investigate if Rht8 has a similar dwarfing effect on the size of leaf cells to reduce leaf area. METHODS: The effect of Rht8 on cell size and leaf area was assessed in four types of epidermal cells (interstomatal, long, sister and bulliform) measured on leaf 2 of standard height (rht8) and semi-dwarf (Rht8) doubled-haploid lines (DHLs). The DHLs were derived from a cross between very vigorous, standard height (rht8) ('Vigour18') and less vigorous, semi-dwarf (Rht8) ('Chuan-Mai 18') parents. KEY RESULTS: Large differences were observed in seedling vigour between the parents, where 'Vigour18' had a much greater plant leaf area than 'Chuan-Mai 18'. Accordingly, 'Vigour18' had on average longer, wider and more epidermal cells and cell files than 'Chuan-Mai 18'. Although there was correspondingly large genotypic variation among DHLs for these traits, the contrast between semi-dwarf Rht8 and tall rht8 DHLs revealed no difference in the size of leaf 2 or average cell characteristics. Hence, these traits were independent of plant height and therefore Rht8 in the DHLs. Correlations for leaf and average cell size across DHLs revealed a strong and positive relationship between leaf width and cell files, while the relationships between leaf and cell width, and leaf and cell length were not statistically different. The relative contribution of the four cell types (long, sister, interstomatal and bulliform) to leaf size in the parents, comparative controls and DHLs is discussed. CONCLUSIONS: Despite a large range in early vigour among the DHLs, none of the DHLs attained the leaf area or epidermal cell size and numbers of the vigorous rht8 parent. Nonetheless, the potential exists to increase the early vigour of semi-dwarf wheats by using GA-sensitive dwarfing genes such as Rht8.     

Novel Natural Allelic Variations at the Rht-1 Loci in Wheat

Plant height is an important agronomic trait. Dramatic increase in wheat yield during the“green revolution”is mainly due to the widespread utilization of the Reduced height (Rht)-1 gene. We analyzed th...     

Comparative molecular mapping of GA insensitive Rht loci on chromosomes 4B and 4D of common wheat (Triticum aestivum L.)

 The two GA-insensitive dwarfing gene loci Rht-B1 and Rht-D1 were mapped using three F₂ populations, segregating for Rht-B1c (Rht3), Rht-D1b (Rht2) or Rht-D1c (Rht10). Rht-B1c was mapped on chromosome 4BS in the centromere region, distal and closely linked to the RFLP markers Xpsr144 (11.9 cM) and Xpsr584 (17.8 cM), but proximal to Xmwg634 (30 cM). Rht-D1c, however, was found to be closely linked to the distally located markers Xpsr921 (0.8 cM) and Xmwg634 (1.5 cM). The homoeologous relationships between the GA-insensitive dwarfing genes within the Triticeae are discussed. Received: 2 May 1997 / Accepted: 9 June 1997     

Whole Genome Association Mapping of Plant Height in Winter Wheat (Triticum aestivum L.)

The genetic architecture of plant height was investigated in a set of 358 recent European winter wheat varieties plus 14 spring wheat varieties based on field data in eight environments. Genotyping of diagnostic markers revealed the Rht-D1b mutant allele in 58% of the investigated varieties, while the Rht-B1b mutant was only present in 7% of the varieties. Rht-D1 was significantly associated with plant height by using a mixed linear model and employing a kinship matrix to correct for population stratification. Further genotyping data included 732 microsatellite markers, resulting in 770 loci, of which 635 markers were placed on the ITMI map plus a set of 7769 mapped SNP markers genotyped with the 90 k iSELECT chip. When Bonferroni correction was applied, a total of 153 significant marker-trait associations (MTAs) were observed for plant height and the SSR markers (−log₁₀ (P-value) ≥4.82) and 280 (−log₁₀ (P-value) ≥5.89) for the SNPs. Linear regression between the most effective markers and the BLUEs for plant height indicated additive effects for the MTAs of different chromosomal regions. Analysis of syntenic regions in the rice genome revealed closely linked rice genes related to gibberellin acid (GA) metabolism and perception, i.e. GA20 and GA2 oxidases orthologous to wheat chromosomes 1A, 2A, 3A, 3B, 5B, 5D and 7B, ent-kaurenoic acid oxidase orthologous to wheat chromosome 7A, ent-kaurene synthase on wheat chromosome 2B, as well as GA-receptors like DELLA genes orthologous to wheat chromosomes 4B, 4D and 7A and genes of the GID family orthologous to chromosomes 2B and 5B. The data indicated that besides the widely used GA-insensitive dwarfing genes Rht-B1 and Rht-D1 there is a wide spectrum of loci available that could be used for modulating plant height in variety development.     

Molecular mapping of gibberellin-responsive dwarfing genes in bread wheat

Opportunities exist for replacing reduced height (Rht) genes Rht-B1b and Rht-D1b with alternative dwarfing genes for bread wheat improvement. In this study, the chromosomal locations of several height-reducing genes were determined by screening populations of recombinant inbred lines or doubled haploid lines varying for plant height with microsatellite markers. Linked markers were found for Rht5 (on chromosome 3BS), Rht12 (5AL) and Rht13 (7BS), which accounted for most of the phenotypic variance in height in the respective populations. Large height differences between genotypes (up to 43 cm) indicated linkage to major height-reducing genes. Rht4 was associated with molecular markers on chromosome 2BL, accounting for up to 30% of the variance in height. Confirming previous studies, Rht8 was linked to markers on chromosome 2DS, whereas a population varying for Rht9 revealed a region with a small but significant height effect on chromosome 5AL. The height-reducing effect of these dwarfing genes was repeatable across a range of environments. The molecular markers developed in this study will be useful for marker-assisted selection of alternative height-reducing genes, and to better understand the effects of different Rht genes on wheat growth and agronomic performance.     

The 'Green Revolution' dwarfing genes play a role in disease resistance in Triticum aestivum and Hordeum vulgare

The Green Revolution dwarfing genes, Rht-B1b and Rht-D1b, encode mutant forms of DELLA proteins and are present in most modern wheat varieties. DELLA proteins have been implicated in the response to biotic stress in the model plant, Arabidopsis thaliana. Using defined wheat Rht near-isogenic lines and barley Sln1 gain of function (GoF) and loss of function (LoF) lines, the role of DELLA in response to biotic stress was investigated in pathosystems representing contrasting trophic styles (biotrophic, hemibiotrophic, and necrotrophic). GoF mutant alleles in wheat and barley confer a resistance trade-off with increased susceptibility to biotrophic pathogens and increased resistance to necrotrophic pathogens whilst the converse was conferred by a LoF mutant allele. The polyploid nature of the wheat genome buffered the effect of single Rht GoF mutations relative to barley (diploid), particularly in respect of increased susceptibility to biotrophic pathogens. A role for DELLA in controlling cell death responses is proposed. Similar to Arabidopsis, a resistance trade-off to pathogens with contrasting pathogenic lifestyles has been identified in monocotyledonous cereal species. Appreciation of the pleiotropic role of DELLA in biotic stress responses in cereals has implications for plant breeding.     

Semi-dwarfing Rht-B1 and Rht-D1 loci of wheat differ significantly in their influence on resistance to Fusarium head blight

Fusarium head blight (FHB) is an important disease of wheat worldwide. Soissons is one of the most resistant varieties grown in UK. The current study was undertaken to identify QTL for FHB resistance in Soissons and to determine whether the semi-dwarfing alleles Rht-B1b and Rht-D1b have a similar influence on susceptibility to FHB. A Soissons (Rht-B1b; Rht-D1a) × Orvantis (Rht-B1a; Rht-D1b) doubled haploid (DH) population was assessed for FHB resistance in three trials. Soissons contributed a single, stable major FHB QTL linked to the Rht-D1 locus. In contrast, the Rht-B1b allele (contributed by Soissons) conferred no negative effect on FHB resistance, even conferring a very minor positive effect in one trial. The influence of the Rht-B1b and Rht-D1b alleles on FHB resistance was further investigated using both Mercia and Maris Huntsman near-isogenic lines. Under high disease pressure both Rht-B1b and Rht-D1b significantly decreased Type 1 resistance (resistance to initial infection). However, whilst Rht-D1b has no effect on Type 2 resistance (resistance to spread of the fungus within the spike), Rht-B1b significantly increased Type 2 resistance. Our study demonstrates that the choice of semi-dwarfing gene used in plant breeding programmes may be a significant consideration where resistance to FHB is an important breeding target.     

A tandem segmental duplication (TSD) in green revolution gene Rht-D1b region underlies plant height variation

? Rht-D1c (Rht10) carried by Chinese wheat (Triticum aestivum) line Aibian 1 is an allele at the Rht-D1 locus. Among the Rht-1 alleles, little is known about Rht-D1c although it determines an extreme dwarf phenotype in wheat. ? Here, we cloned and functionally characterized Rht-D1c using a combination of Southern blotting, target region sequencing, gene expression analysis and transgenic experiments. ? We found that the Rht-D1c allele was generated through a tandem segmental duplication (TSD) of a >?1?Mb region, resulting in two copies of the Rht-D1b. Two copies of Rht-D1b in the TSD were three-fold more effective in reducing plant height than a single copy, and transformation with a segment containing the tandemly duplicated copy of Rht-D1b resulted in the same level of reduction of plant height as the original copy in Aibian 1. ? Our results suggest that changes in gene copy number are one of the important sources of genetic diversity and some of these changes could be directly associated with important traits in crops.     

Mapping gibberellin-sensitive dwarfing locus <Emphasis Type="Italic">Rht18</Emphasis> in durum wheat and development of SSR and SNP markers for selection in breeding

Gibberellin-sensitive dwarfing gene Rht18 was mapped in two durum wheat recombinant inbred lines (RIL) populations developed from crosses, Bijaga Yellow/Icaro and HI 8498/Icaro. Rht18 was mapped within genetic interval of 1.8 cM on chromosome 6A. Simple sequence repeat (SSR) markers S470865SSR4, barc37 and TdGA2ox-A9 specific marker showed co-segregation with Rht18 in Bijaga Yellow/Icaro population consisting 256 RILs. Effect of Rht18 on plant height was validated in HI 8498/Icaro RIL population which segregated for Rht18 and Rht-B1b. Rht-B1b from HI 8498 showed pleiotropic effect on plant height and coleoptile length, on the other hand, Rht18 did not show effect on coleoptile length. The SSR and SNP markers linked to Rht18 were also validated by assessing their allelic frequency in 89 diverse durum and bread wheat accessions. It was observed that 204 bp allele of S470865SSR4 could differentiate Icaro from rest of the wheat accessions except HI 8498, suggesting its utility for selection of Rht18 in wheat improvement programs. Rht18 associated alleles of TdGA2ox-A9, IAW4371 and IAW7940 were absent in most of the tall Indian local durum wheat and bread wheat, hence could be used to transfer Rht18 to bread wheat and local durum wheat. SSR marker barc3 showed high recombination frequency with Rht18, though it showed allele unique to Icaro. Since semidwarf wheat with GA-sensitive dwarfing genes are useful in dry environments owing to their longer coleoptile, better emergence and seedling vigor, Rht18 may provide a useful alternative to widely used GA-insensitive dwarfing genes under dry environments.     

Dominant and pleiotropic effects of a GAI gene in wheat results from a lack of interaction between DELLA and GID1

Dominance, semidominance, and recessiveness are important modes of Mendelian inheritance. The phytohormone gibberellin (GA) regulates many plant growth and developmental processes. The previously cloned semidominant GA-insensitive (GAI) genes Reduced height1 (Rht1) and Rht2 in wheat (Triticum aestivum) were the basis of the Green Revolution. However, no completely dominant GAI gene has been cloned. Here, we report the molecular characterization of Rht-B1c, a dominant GAI allele in wheat that confers more extreme characteristics than its incompletely dominant alleles. Rht-B1c is caused by a terminal repeat retrotransposons in miniature insertion in the DELLA domain. Yeast two-hybrid assays showed that Rht-B1c protein fails to interact with GA-INSENSITIVE DWARF1 (GID1), thereby blocking GA responses and resulting in extreme dwarfism and pleiotropic effects. By contrast, Rht-B1b protein only reduces interaction with GID1. Furthermore, we analyzed its functions using near-isogenic lines and examined its molecular mechanisms in transgenic rice. These results indicated that the affinity between GID1 and DELLA proteins is key to regulation of the stability of DELLA proteins, and differential interactions determine dominant and semidominant gene responses to GA.     

Comparative mapping of a gibberellic acid-insensitive dwarfing gene (Dwf2) on chromosome 4HS in barley

 We report the genetic mapping of Dwf2, a dominant gibberellic acid (GA₃)-insensitive dwarfing gene which has been previously described to cause a very short growth habit in barley (Hordeum vulgare) mutant ‘93/B694’. Using RFLP and microsatellite markers we performed segregation analysis in an F₂ population comprising 86 individuals developed from a cross of ‘93/B694’ (Dwf2) with ‘Bonus M2’ (dwf2). Dwf2 was mapped on the short arm of barley chromosome 4H proximal to microsatellite marker XhvOle (5.7 cM) and distal to RFLP marker Xmwg2299 (18.3 cM). The genetic localization of the Dwf2 gene at a homoeologous position to the multiallelic Rht-B1 and Rht-D1 loci in wheat suggests synteny of GA-insensitive dwarfing genes within the Triticeae. Moreover, the extremely prostrate growth habit exhibited in barley ‘93/B694’ (Dwf2) resembles that of wheat plants carrying the genes Rht-B1c (Rht3) or Rht-D1c (Rht10). Received: 1 July 1998 / Accepted: 17 September 1998     

GA-Responsive Dwarfing Gene Rht12 Affects the Developmental and Agronomic Traits in Common Bread Wheat

Opportunities exist for replacing reduced height (Rht) genes Rht-B1b and Rht-D1b with alternative dwarfing genes, such as the gibberellin-responsive gene Rht12, for bread wheat improvement. However, a comprehensive understanding of the effects and mode of action of Rht12 is lacking. In the present study, the effects of Rht12 were characterized by analyzing its effects on seeding vigour, seedling roots, leaf and stem morphology, spike development and carbohydrate assimilation and distribution. This was carried out in the four genotypes of F_2:3 lines derived from a cross between Ningchun45 and Karcagi (12) in two experiments of autumn sowing and spring sowing. Rht12 significantly decreased stem length (43%∼48% for peduncle) and leaf length (25%∼30% for flag leaf) while the thickness of the internode walls and width of the leaves were increased. Though the final plant stature was shortened (40%) by Rht12, the seedling vigour, especially coleoptile length and root traits at the seedling stage, were not affected adversely. Rht12 elongated the duration of the spike development phase, improved the proportion of spike dry weight at anthesis and significantly increased floret fertility (14%) in the autumn sowing experiment. However, Rht12 delayed anthesis date by around 5 days and even the dominant Vrn-B1 allele could not compensate this negative effect. Additionally, grain size was reduced with the ability to support spike development after anthesis decreased in Rht12 lines. Finally, grain yield was similar between the dwarf and tall lines in the autumn sowing experiment. Thus, Rht12 could substantially reduce plant height without altering seeding vigour and significantly increase spikelet fertility in the favourable autumn sowing environment. The successful utilization of Rht12 in breeding programs will require careful selection since it might delay ear emergence. Nonetheless, the potential exists for wheat improvement by using Rht12.     

Exogenous GA3 Application Can Compensate the Morphogenetic Effects of the GA-Responsive Dwarfing Gene Rht12 in Bread Wheat

The most common dwarfing genes in wheat, Rht-B1b and Rht-D1b, classified as gibberellin-insensitive (GAI) dwarfing genes due to their reduced response to exogenous GA, have been verified as encoding negative regulators of gibberellin signaling. In contrast, the response of gibberellin-responsive (GAR) dwarfing genes, such as Rht12, to exogenous GA is still unclear and the role of them, if any, in GA biosynthesis or signaling is unknown. The responses of Rht12 to exogenous GA₃ were investigated on seedling vigour, spike phenological development, plant height and other agronomic traits, using F_2∶3 and F_3∶4 lines derived from a cross between Ningchun45 and Karcagi-12 in three experiments. The application of exogenous GA₃ significantly increased coleoptile length and seedling leaf 1 length and area. While there was no significant difference between the dwarf and the tall lines at the seedling stage in the responsiveness to GA₃, plant height was significantly increased, by 41 cm (53%) averaged across the three experiments, in the GA₃-treated Rht12 dwarf lines. Plant height of the tall lines was not affected significantly by GA₃ treatment (<10 cm increased). Plant biomass and seed size of the GA₃-treated dwarf lines was significantly increased compared with untreated dwarf plants while there was no such difference in the tall lines. GA₃-treated Rht12 dwarf plants with the dominant Vrn-B1 developed faster than untreated plants and reached double ridge stage 57 days, 11 days and 50 days earlier and finally flowered earlier by almost 7 days while the GA₃-treated tall lines flowering only 1–2 days earlier than the untreated tall lines. Thus, it is clear that exogenous GA₃ can break the masking effect of Rht12 on Vrn-B1 and also restore other characters of Rht12 to normal. It suggested that Rht12 mutants may be deficient in GA biosynthesis rather than in GA signal transduction like the GA-insensitive dwarfs.     

Novel Genetic Variants of GA-Insensitive Rht-1 Genes in Hexaploid Wheat and Their Potential Agronomic Value

This study has found numerous novel genetic variants of GA-insensitive dwarfing genes with potential agricultural value for crop improvement. The cultivar, Spica is a tall genotype and possesses the wild-type genes of Rht-A1a, Rht-B1a and Rht-D1a. The cultivar Quarrion possesses a null mutant in the DELLA motif in each of the 3 genomes. This is a first report of a null mutant of Rht-A1. In addition, novel null mutants which differ from reported null alleles of Rht-B1b, Rht-B1e and Rht-D1b have been found in Quarrion, Carnamah and Whistler. The accession, Aus1408 has an allele of Rht-B1 with a mutation in the conserved ‘TVHYNP’ N-terminal signal binding domain with possible implications on its sensitivity to GA. Mutations in the conserved C-terminal GRAS domain of Rht-A1 alleles with possible effects on expression have been found in WW1842, Quarrion and Drysdale. Genetic variants with putative spliceosomal introns in the GRAS domain have been found in all accessions except Spica. Genome-specific cis-sequences about 124 bp upstream of the start codon of the Rht-1 gene have been identified for each of the three genomes.     

Haplotype variation of Green Revolution gene Rht-D1 during wheat domestication and improvement

Green Revolution made a substantial contribution to wheat yields worldwide in the 1960 s and 1970 s. It is of great importance to analyze the haplotype variation of Rht-D1, the Green Revolution gene, during wheat(Triticum aestivum L.)domestication and breeding to understand its evolution and function in wheat breeding history. In this study, the Rht-D1 and its flanking regions were sequenced and single nucleotide polymorphisms were detected based on a panel of 45 accessions of Aegilops tauschii, 51 accessions of landraces and 80 accessions of commercial varieties. Genetic diversity in the wild accessions was much higher than that in the varieties and higher than that reported previously. Seven haplotypes(Hapl I to Hapl VII) of Rht-D1 were identified and their evolutionary relationships were proposed. In addition to the well-known Green Revolution allele Rht-D1b, Hapl VII(an allele Rht-D1k) was identified in early breeding varieties, which reduced plant height by 16%. The results suggested that Rht-D1k had been used in breeding before the Green Revolution and made a great contribution to wheat production worldwide.Based on the breeding history and molecular evidence, we proposed that the wheat Green Revolution in China and International Maize and Wheat Improvement Center(CIMMYT)occurred independently.