The Effects of Dwarfing Genes (Rht-B1b, Rht-D1b, and Rht8) with Different Sensitivity to GA_3 on the Coleoptile Length and Plant Height of Wheat

Understanding the effects of wheat dwarfing genes on the coleoptile length and plant height is crucial for the proper utilization of dwarfing genes in the improvement of wheat yield. Molecular marker analysis combined with pedigree information were used to classify wheat cultivars widely planted in major wheat growing regions in China into different categories based on the dwarfing genes they carried. The effects of the dwarfing genes with different sensitivity to gibberellins （GA3） on the coleoptile length and plant height were analyzed. Screening of 129 cultivars by molecular marker analysis revealed that 58 genotypes of wheat contained the dwarfing gene Rht-B1b, 24 genotypes of wheat contained Rht-D1b gene and 73 genotypes of wheat possessed Rht8 gene. In addition, among these 129 cultivars, 35 genotypes of wheat cultivars contained both Rht-B1b and Rht8 genes and 16 genotypes of wheat cultivars contained both Rht-D1b and Rht8 genes. Wheat cultivars with the dwarfing genes Rht-B1b or Rht-D1b were insensitive to GA3, while the cultivars with the dwarfing gene Rht8 were sensitive to GA3. Most of the wheat genotypes containing combination of Rht8 gene with either Rht-B1b or Rht-D1b gene were insensitive to GA3. The plant height was reduced by 24.6, 30.4, 28.2, and 32.2%, respectively, for the wheat cultivars containing Rht-B1b, Rht-D1b, Rht-B1b ＋ Rht8, and Rht-D1b ＋ Rht8 genes. The plant height was reduced by 14.3% for the wheat cultivar containing GA3-sensitive gene Rht8. The coleoptile length was shortened by 25.4, 31.3, 28.4 and 31.3%, respectively, in the wheat cultivars containing Rht-B1b, Rht-D1b, Rht-B1b ＋Rht8 and Rht-D1b ＋ Rht8 genes, while the coleoptile length was shortened only by 6.2% for the wheat cultivar containing Rht8 gene. We conclude that GA3-insensitive dwarfing genes （Rht-B1b and Rht-D1b） are not suitable for the wheat improvement in dryland because these two genes have effect on reducing both plant height and coleoptile length. In contrast, GA3- sensitive dwarfing gene （Rht8） is a relatively ideal candidate for the wheat improvement since it significantly reduces the plant height of wheat, but has less effect on the coleoptile length.

The Value of Different GA Insensitive Rht Dwarfing Genes in Winter Wheat Breeding

The value of different dwarfing genes in winter wheat breeding was studied using 6 near-isogenic lines carrying different Rht dwarfing genes over three years experiment.Results showed that both the Rht1 and Rht2 semi-dwarfing genes had significantlypositive effects on kernel number and grain weight per spike, and had significantlynegative effects on 1000-grain weight comparing to the tall line(rht) and the Rht3 line.The Rht3 dwarfing gene had a significantly negative effect on kernel number per spike,and had positive effect on 1000-grain weight. The combination of the Rht2 and Rht3 geneshowed significantly negative effect on yield components. All of these 5 dwarfing orsemidwarfing genotypes mentioned above had a significantly negative effect on plantheight and no significant effect on the area of flag leaf, spikelets per spike and spikelength.

Analysis on the Dwarfing Genes in Zhepi 1 and Aizao 3:Two Dwarfing Gene Donors in Barley Breeding in China

Inheritance of plant height was studied in the two dwarfing gene donors, Zhepi 1 and Aizao 3, in barley breeding in China. Using direct cross and para-back-cross methods, allelic tests were carried out not only between the dwarfing genes in Zhepi 1 and Aizao 3, but also with br, uzu, denso, or sdwl and the six novel dwarfing genes that have been recently identified in barley in China. The results showed that the plant height was attributed to Mendelian inheritance of a recessive dwarfing gene both in Zhepi 1 and Aizao 3. The dwarfing genes carried by the two cultivars were the same, but different from the three known and the six novel dwarfing genes. On the basis of the present study, only two dwarfing genes have been used in barley breeding in China since 1950.

Effects of dwarfing genes on water use efficiency of bread wheat

Climate change has increased the risk of drought, which significantly limits plant productivity.Various ways of increasing water availability and sustaining growth of crop plants in drought-prone environments are available. Genetic advances in grain yields under rainfed conditions have been achieved with the introduction of dwarfing genes. A thorough understanding of the effects of different dwarfing genes on root growth, coleoptile length, grain yields and water using efficiency(WUE) will provide opportunities to select appropriate Rht genes for breeding high WUE and grain yield cultivars. This review focuses on the mechanism involved in Rht genes that reduce plant height and affect root and coleoptile length, their consequent effects on grain yields and WUE, and suggests that for rainfed and irrigation-limited environments, combining GAR and GAI dwarfing genes in breeding may help boost WUE and yields, and more materials from different parental sources should be collected to assess opportunities for potential comprehensive application of specific Rht genes.

Identification of SSR Marker Linked to a Major Dwarfing Gene in Common Wheat

A segregating population with 410 F2 individuals from the cross MERCIA （Rht-Bla）×Dwarf 123 was made to identify a new major dwarfing gene carrying by novel wheat germplasm Dwarf 123. Combination of bulk segerant analysis method was used. A total of 145 SSR markers were tested for polymorphisms among parental lines and DNA bulks of F2 population. Out of 145 primer pairs only three markers revealed corresponding polymorphism among parental lines and F2 DNA bulks. The marker Barc20 was close to the dwarfing gene with a genetic distance of 1.8 cM, and markers Gwm513 and Gwm495 were linked to the gene with genetic distance of 6.7 and 13 cM, respectively. Linkage analysis mapped the dwarfing gene to the long arm of chromosome 4B with the order of Barc20-dwarfing gene-Gwm513-Gwm495. The Comparision between the new gene and the known Rht-B1 alleles showed that dwarfing gene Rht-Ai123 was different from the others. The identification of the new dwarfing gene and its linked markers will greatly facilitate its utilization in wheat high yield breeding for reducing plant height.

Expansin Genes Expressed Differentially in Peduncle Elongation of Near-Isogenic Wheat Rht Lines

The introduction of reduced height （Rht） genes Rht-Blb and Rht-Dlb led to impressive increases in wheat （Triticum aestivum L.） yields during the Green Revolution. In the present study, the dynamic elongation of peduncle in a set ofnear-isogenic lines （NILs） carrying different Rht alleles （Rht-Blb, Rht-Dlb, Rht-Blc, Rht-Dlb＋Rht-Blb, and Rht-Dlb＋Rht-Blc） were investigated. The reduction of the final length of peduncle in NILs was dependent mainly on the elongation rate, which was reduced by Rht genes, during rapid elongation phase. Resin sections showed that Rht genes strongly reduced the cell extension in peduncle. The expression of expansin genes, which mediate cell wall loosening and leading to cell expansion, were analysed by using real- time quantitative PCR （qPCR）. Among the 23 possible wheat expansin genes, 17 were expressed in the peduncle. The spatial distribution of expression was further analysed for five expansins that showed high expression levels in the peduncles of Rht lines. Compared to wild type plants, the incorporation of Rht-Dlb allele decreased about 37 and 80% of the expression levels of ExpA 7 and ExpA3 in elongation zone, respectively. The presence Rht-Blc dwarfing genes, however, produced 53% reduction in the expression level of ExpA7, and seriously decreased about 70% of ExpB9 expression. Although the expression levels of five genes exhibited variability among the lines, an expansin gene, ExpB2, showed its expression level highly associated with the cell elongation rate in peduncle of different Rht lines.

Cloning and Expression Analysis of a Brassinosteroid Biosynthetic Enzyme Gene,GhDWF1,from Cotton (Gossypium hirsuturm L.)

Brassinosteroids （BRs） are an important class of plant steroidal hormones that are essential in a wide variety of physiological processes. To determine the effects of BRs on the development of cotton fibers, through screening cotton fiber EST database and contigging the candidate ESTs, a key gene （GhDWF1） involved in the upstream biosynthetic pathway of BRs was cloned from developing fibers of upland cotton （Gossypium hirsutum L.） cv. Xuzhou 142. The full length of the cloned cDNA is 1 849 bp, including a 37 bp 5＇-untranslated region, an ORF of 1 692 bp, and a 120 bp 3＇-untranslated region. The cDNA encodes a polypeptide of 563 amino acid residues with a predicted molecular mass of 65 kD. The deduced amino acid sequence has high homology with the BR biosynthetic enzyme, DWARF1/DIMINUTO, from rice, maize, pea, tomato, and Arabidopsis. Furthermore, the typical conserved structures, such as the transmembrane domain, the FAD- dependent oxidase domain, and the FAD-binding site, are present in the GhDWF1 protein. The Southern blot indicated that the GhDWF1 gene is a single copy in upland cotton genome. RT-PCR analysis revealed that the highest level of GhDWF1 expression was detected in 0 DPA （day post anthesis） ovule （with fibers） while the lowest level was observed in cotyledon. The GhDWF1 gene presents high expression levels in root, young stem, and fiber, especially, at the fiber developmental stage of secondary cell wall accumulation. Moreover, the expression level was higher in ovules （with fibers） of wildtype （Xuzhou 142） than in ovules of fuzzless-lintless mutant at the same developmental stages （0 and 4 DPA）. The results suggest that the GhDWF1 gene plays a crucial role in fiber development.

Genetic Identification of a New Small Grain Dwarf Gene in Rice

The plant material used in the study was rice line 162d, a new small grain dwarf mutant. Polymorphic analysis of 221 SSR loci demonstrated that 162d derived from a semidwarf variety Shuhui 162 through mutation, and 162d and Shuhui 162 were just a pair of near isogenic lines. Genetic analysis of F_1 and F_2 populations suggested that dwarfism in 162d was controlled by a single recessive gene. Phenotypic characteristics of the mutant gene were that plant height was about a quarter of normal height, grain size about a quarter of normal size, leaf was short and broad, and seed setting rate was very low, compared with the near isogenic line Shuhui 162. The mutant gene was sensitive to gibberellin (GA_3) treatment and did not located on the region near the centromere of rice chromosome 5, where dl gene located. Therefore, it was concluded that the mutant gene of 162d was a new small grain dwarf gene in rice.

Genetic Analysis and Mapping of the Dominant Dwarfing Gene D-53 in Rice

The dwarfing gene D-53 Is one of a few dominant genes for dwarfing In rice （Oryza satlva L.）. In the present study, our genetic analysis confirmed that mutant characteristics including dwarfing, profuse tlllerlng, thin stems and small panicles are all controlled by the dominant D-53 gene. We measured the length of each Internode of KL908, a D-53-carrylng line, and classified the dwarfism of KL908 Into the dn-type. In addition, we measured elongation of the second sheath and a-amylase activity In the endosperm, and we characterized KL908 as a dwarf mutant that was neither glbberelllc acid-deficient nor glbberelllc acid-Insensitive. Using a large F2 population obtained by crossing KL908 with a wild-type variety, NJ6, the D-53 gene was mapped to the terminal region of the short arm of chromosome 11, with one simple sequence repeat marker, Ds3, co-segregating, and the other, K81114, located 0.6 cM away.