Updated guidelines for gene nomenclature in wheat.

KEY MESSAGE: Here, we provide an updated set of guidelines for naming genes in wheat that has been endorsed by the wheat research community. The last decade has seen a proliferation in genomic resources for wheat, including reference- and pan-genome assemblies with gene annotations, which provide new opportunities to detect, characterise, and describe genes that influence traits of interest. The expansion of genetic information has supported growth of the wheat research community and catalysed strong interest in the genes that control agronomically important traits, such as yield, pathogen resistance, grain quality, and abiotic stress tolerance. To accommodate these developments, we present an updated set of guidelines for gene nomenclature in wheat. These guidelines can be used to describe loci identified based on morphological or phenotypic features or to name genes based on sequence information, such as similarity to genes characterised in other species or the biochemical properties of the encoded protein. The updated guidelines provide a flexible system that is not overly prescriptive but provides structure and a common framework for naming genes in wheat, which may be extended to related cereal species. We propose these guidelines be used henceforth by the wheat research community to facilitate integration of data from independent studies and allow broader and more efficient use of text and data mining approaches, which will ultimately help further accelerate wheat research and breeding.

A multiple resistance locus on chromosome arm 3BS in wheat confers resistance to stem rust (Sr2), leaf rust (Lr27) and powdery mildew.

Sr2 is the only known durable, race non-specific adult plant stem rust resistance gene in wheat. The Sr2 gene was shown to be tightly linked to the leaf rust resistance gene Lr27 and to powdery mildew resistance. An analysis of recombinants and mutants suggests that a single gene on chromosome arm 3BS may be responsible for resistance to these three fungal pathogens. The resistance functions of the Sr2 locus are compared and contrasted with those of the adult plant resistance gene Lr34.

Anticipatory breeding for resistance to rust diseases in wheat.

Anticipatory resistance breeding is the process of predicting future pathotypes and producing resistant germplasm to avert future losses. It is made possible by a national pathotype surveillance program and knowledge that new pathotypes arise predominantly from mutation in existing pathotypes. This is supported by genetic analyses to catalogue the identity and distribution of resistance genes in current cultivars. A national germplasm enhancement program ensuring that both currently effective and potentially new sources of resistance are available in a wide range of adapted genotypes enables rapid cultivar replacement before or soon after the occurrence of new pathotypes. The policy of recommending only rust-resistant cultivars in the more rust-prone areas has resulted in significant reductions in pathogen population size and variability. With increased and more rapid international human travel and transport, there is an increased threat of exotic pathotypes, the effects of which are more difficult to predict. As the frequency and magnitude of epidemics decline, public awareness programs will be required to achieve and maintain the use of rust resistance by the entire wheat industry.

Fine genetic mapping fails to dissociate durable stem rust resistance gene Sr2 from pseudo-black chaff in common wheat (Triticum aestivum L.).

The broad-spectrum stem rust resistance gene Sr2 has provided protection in wheat against Puccinia graminis Pers. f. sp. tritici for over 80 years. The Sr2 gene and an associated dark pigmentation trait, pseudo-black chaff (PBC), have previously been localized to the short arm of chromosome 3B. In a first step towards the positional-based cloning of Sr2, we constructed a high-resolution map of this region. The wheat EST (wEST) deletion bin mapping project provided tightly linked cDNA markers. The rice genome sequence was used to infer the putative gene order for orthologous wheat genes and provide additional markers once the syntenic interval in rice was identified. We used this approach to map six wESTs that were collinear with the physical order of the corresponding genes on rice chromosome 1 suggesting there are no major re-arrangements between wheat and rice in this region. We were unable to separate by recombination the tightly linked morphological trait, PBC from the stem rust resistance gene suggesting that either a single gene or two tightly linked genes control both traits.

Powdery mildew resistance and Lr34/Yr18 genes for durable resistance to leaf and stripe rust cosegregate at a locus on the short arm of chromosome 7D of wheat.

The incorporation of effective and durable disease resistance is an important breeding objective for wheat improvement. The leaf rust resistance gene Lr34 and stripe rust resistance gene Yr18 are effective at the adult plant stage and have provided moderate levels of durable resistance to leaf rust caused by Puccinia triticina Eriks. and to stripe rust caused by Puccinia striiformis Westend. f. sp. tritici. These genes have not been separated by recombination and map to chromosome 7DS in wheat. In a population of 110 F(7) lines derived from a Thatcher x Thatcher isogenic line with Lr34/Yr18, field resistance to leaf rust conferred by Lr34 and to stripe rust resistance conferred by Yr18 cosegregated with adult plant resistance to powdery mildew caused by Blumeria graminis (DC) EO Speer f. sp. tritici. Lr34 and Yr18 were previously shown to be associated with enhanced stem rust resistance and tolerance to barley yellow dwarf virus infection. This chromosomal region in wheat has now been linked with resistance to five different pathogens. The Lr34/Yr18 phenotypes and associated powdery mildew resistance were mapped to a single locus flanked by microsatellite loci Xgwm1220 and Xgwm295 on chromosome 7DS.

High-resolution mapping and mutation analysis separate the rust resistance genes Sr31, Lr26 and Yr9 on the short arm of rye chromosome 1.

The stem, leaf and stripe rust resistance genes Sr31, Lr26 and Yr9, located on the short arm of rye chromosome 1, have been widely used in wheat by means of wheat-rye translocation chromosomes. Previous studies have suggested that these resistance specificities are encoded by either closely-linked genes, or by a single gene capable of recognizing all three rust species. To investigate these issues, two 1BL.1RS wheat lines, one with and one without Sr31, Lr26 and Yr9, were used as parents for a high-resolution F2 mapping family. Thirty-six recombinants were identified between two PCR markers 2.3 cM apart that flanked the resistance locus. In one recombinant, Lr26 was separated from Sr31 and Yr9. Mutation studies recovered mutants that separated all three rust resistance genes. Thus, together, the recombination and mutation studies suggest that Sr31, Lr26 and Yr9 are separate closely-linked genes. An additional 16 DNA markers were mapped in this region. Multiple RFLP markers, identified using part of the barley Mla powdery mildew resistance gene as probe, co-segregated with Sr31 and Yr9. One deletion mutant that had lost Sr31, Lr26 and Yr9 retained all Mla markers, suggesting that the family of genes on 1RS identified by the Mla probe does not contain the Sr31, Lr26 or Yr9 genes. The genetic stocks and DNA markers generated from this study should facilitate the future cloning of Sr31, Lr26 and Yr9.

Cytogenetic studies in wheat. XV. Location of rust resistance genes in VPM1 and their genetic linkage with other disease resistance genes in chromosome 2A.

Inheritance studies showed that the VPM1-derived seedling resistances to stem rust, stripe rust, leaf rust, and powdery mildew were controlled by single genes; the genes for rust resistance were designated Sr38, Yr17, and Lr37, respectively, whereas the gene for resistance to powdery mildew was postulated to be Pm4b. Sr38, Yr17, and Lr37 were shown to be closely linked and distally located in the short arm of chromosome 2A. They showed very close repulsion linkage with Lr17 and were genetically independent of other genes known to be located in chromosome 2A. Previously unmapped, Yr1 appeared to be distally located in the long arm of chromosome 2A.

Genetics of resistance toPuccinia graminis tritici andPuccinia recondite tritici in four South African wheats.

Genes for resistance toPuccinia graminis tritici andPuccinia recondita tritici identified in four South African wheats were:Sr6,Sr8a,Sr9e, andLr13 in 'W3762';Sr5,Sr8a,Sr9b,Sr12,Sr24,Lr13, andLr24 in 'W3760';Sr2,Sr24,SrC,Lr13, andLr24 in 'W3751'; andSr7a,Sr23,Sr36, andLr16 in 'W3755'. GenesSr2,Sr9e, andSr24 also conferred adult plant resistance to the predominant pathotypes ofP. graminis tritici. GenesSr7a,Sr23, andSrC, when present alone, did not confer acceptable adult plant resistance, even though low seedling reactions were associated with them when tested with the same pathotypes. Genetic recombination betweenLr13 andSr9e was estimated at 12.5%±2.3%.

Genetics of resistance to Puccinia graminis tritici in 'Chris' and 'W3746' wheats.

'Chris' wheat possessed genes Sr5, Sr7a, Sr8a, Sr9g and Sr12. 'W3746', derived from the cross 'Chris'/'Baart', possessed Sr7a and Sr12. The response conferred by Sr7a was influenced by the genetic background. Although Sr7a or Sr12 alone conferred no observable resistance upon adult plants, the adult resistances of 'Chris' and 'W3746' to predominant pathotypes appeared to be associated with the interaction of Sr7a and Sr12, or genes at closely linked loci.

Linkage mapping of genes for resistance to leaf, stem and stripe rusts and ω-secalins on the short arm of rye chromosome 1R.

The genes controlling resistance to three wheat rusts, viz., leaf rust (Lr26), stem rust (Sr31) and stripe or yellow rust (Yr9), and ω-secalins (Sec1), located on the short arm of rye chromosome 1R, were mapped with respect to each other and the centromere. Analysis of 214 seeds (or families derived from them) from testcrosses between a 1BL.1RS/1R heterozygote and 'Chinese Spring' ditelocentric 1BL showed no recombination between the genes for resistance to the three rusts, suggesting very tight linkage or perhaps a single complex locus conferring resistance to the three rusts. The rust resistance genes were located 5.4 ± 1.7 cM from the Sec1 locus, which in turn was located 26.1 ± 4.3 cM from the centromere; the gene order being centromere - Sec1 - Lr26/Sr31/Yr9 - telomere. In a second test-cross, using a different 1BL.1RS translocation which had only stem rust resistance (SrR), the above gene order was confirmed despite a very large proportion of aneuploids (45.8%) among the progeny. Furthermore, a map distance of 16.0 ± 4.8 cM was estimated for SrR and the telomeric heterochromatin (C-band) on 1RS. These results suggest that a very small segment of 1RS chromatin is required to maintain resistance to all three wheat rusts. It should be possible but difficult to separate the rust resistance genes from the secalin gene(s), which are thought to contribute to dough stickiness of wheat-rye translocation lines carrying 1RS.

A storage-protein marker associated with the suppressor of Pm8 for powdery mildew resistance in wheat.

A suppressor of resistance to powdery mildew conferred by Pm8 showed complete association with the presence of a storage-protein marker resolved by electrophoresis on SDS-PAGE gels. This marker was identified as the product of the gliadin allele Gli-A1a. The mildewresponse phenotypes of wheats possessing the 1BL.1RS translocation were completely predictable from electrophoretograms. The suppressor, designated SuPm8, was located on chromosome 1AS. It was specific in its suppression of Pm8, and did not affect the rye-derived resistance phenotypes of wheat lines with Pm17, also located in 1RS, or of lines with Pm7.

Making science accessible to deaf students. The need for science literacy and conceptual teaching.

Upon examination of current literature, there is a noticeable disparity between suggested science teaching practice and what actually happens in the classroom. This disparity may be more pronounced in science classrooms of deaf students for several reasons discussed in this paper. Science education professionals recommend conceptual teaching, but rote, procedural teaching is often the reality. This is a call to arms for teachers of the deaf to teach science conceptually in an effort to afford deaf students more opportunities to grasp meaning and not function merely at the recall level.

Transfer of rye chromosome segments to wheat by a gametocidal system.

A gametocidal chromosome derived from Aegilops triuncialis (3C) induces chromosome mutations in gametes lacking the 3C chromosome in common wheat (Triticum aestivum L.). We combined 3C with chromosome 1R of rye (Secale cereale L.) in a common wheat line to know how efficiently 3C induces transfers of small 1R segments to wheat. In the 811 progeny of this wheat line, we found five wheat chromosomes (2A, 2D, 3D, 5D and 7D) carrying segments of the 1R satellite. Wheat plants carrying these translocations were tested for the presence of a storage protein locus Sec-1 and a cluster of resistance genes for wheat rust diseases, Sr31, Lr26 and Yr9. The 2A and 2D translocations had the Sec-1 and three rust resistance loci. The 3D and 5D translocations had Sr31, Lr26 and Yr9 but not Sec-1. The 7D translocation lacked Sec-1, Lr26 and Yr9, but the presence of Sr31 in this translocation was not determined. This showed that the translocation points fell into three regions of the 1R satellite, namely, proximal to Sec-1, between Sec-1 and the rust resistance loci, and distal to the rust resistance loci. Thus, the 3C gametocidal system was demonstrated to be effective in transferring small rye chromosome segments.

Characterization of rust-resistant wheat-Agropyron intermedium derivatives by C-banding, in situ hybridization and isozyme analysis.

Chromosome constitutions of three wheat-Agropyron intermedium derivatives were identified by C-banding analysis, in situ hybridization using biotin-labeled genomic Ag. intermedium DNA as a probe and isozyme analysis. Lines W44 and W52 were identified as 7Ai-2(7D) and 7Ai-2(7A) chromosome substitution lines carrying the same chromosome pair of Ag. intermedium. The alien chromosome was found to be homoeologous to group 7 based on C-banding, meiotic pairing and isozyme analyses. Line W49 was identified as a wheat Ag. intermedium chromosome translocation line. The breakpoint of the T2AS · 2AL-7Ai-2L translocation is located in the long arm at a fraction length of 0.62, and the transferred Ag. intermedium segment has a size of about 2.4 µm. Lines W44 and W52 expressed Ag. intermedium genes for resistance to leaf rust, stripe rust and stem rust, but only leaf rust resistance was expressed in W49. The results show that the leaf rust resistance gene(s), designated Lr38, is located in the distal half of the long arm of chromosome 7Ai-2, whereas the genes for resistance to stem rust and stripe rust are located either in the short arm or in the proximal region of the long arm of this chromosome.

Intralipid infusion abolishes ability of human serum to cholesterol-load cultured macrophages.

Intralipid is widely used for intravenous alimentation and contains triglyceride-emulsion particles and phospholipid liposomes. After infusion, triglyceride-emulsion particles resemble chylomicron remnants and thus may be atherogenic. On the other hand, intravenous infusion of phospholipid liposomes produces regression of experimental atherosclerosis and abolishes the ability of hypercholesterolemic rabbit plasma to cholesterol-load cultured macrophage foam cells. To determine the net effect of intralipid infusion on cellular cholesterol balance, J-774 macrophages were incubated for 18 hours with human serum obtained before, during, and after a 6-hour infusion of 10% Intralipid. Compared to serum-free medium, pre-infusion serum increased cellular unesterified cholesterol by 76% and cholesteryl ester by 78%. In contrast, serum obtained after the 6-hour infusion reduced cellular unesterified cholesterol by 23% and cholesteryl ester by 15%. Serum obtained 18 hours after the end of the infusion still showed impaired cholesterol-loading ability. Mouse peritoneal macrophages incubated with these serum samples behaved similarly. Compared to pre-infusion serum, postinfusion serum inhibited cellular uptake of 125I-low density lipoprotein and 125I-very low density lipoprotein by 50% and 80%, respectively, and also enhanced the efflux of cellular cholesterol by 46%. We conclude that the ability of human serum to cause cholesterol accumulation in cultured macrophages is abolished by an infusion of Intralipid. This effect is mediated by a reduction in cholesterol uptake by the cells and by an increase in cell cholesterol efflux. If similar events occur in the arterial wall, Intralipid infusion might inhibit foam cell formation in vivo.

Yr32 for resistance to stripe (yellow) rust present in the wheat cultivar Carstens V.

Stripe or yellow rust of wheat, caused by Puccinia striiformis f. sp. tritici, is an important disease in many wheat-growing regions of the world. A number of major genes providing resistance to stripe rust have been used in breeding, including one gene that is present in the differential tester Carstens V. The objective of this study was to locate and map a stripe rust resistance gene transferred from Carstens V to Avocet S and to use molecular tools to locate a number of genes segregating in the cross Savannah/Senat. One of the genes present in Senat was predicted to be a gene that is present in Carstens V. For this latter purpose, stripe rust response data from both seedling and field tests on a doubled haploid population consisting of 77 lines were compared to an available molecular map for the same lines using a non-parametric quantitative trait loci (QTL) analysis. Results obtained in Denmark suggested that a strong component of resistance with the specificity of Carstens V was located in chromosome arm 2AL, and this was consistent with chromosome location work undertaken in Australia. Since this gene segregated independently of Yr1, the only other stripe rust resistance gene known to be located in this chromosome arm, it was designated Yr32. Further QTLs originating from Senat were located in chromosomes 1BL, 4D, and 7DS and from Savannah on 5B, but it was not possible to characterize them as unique resistance genes in any definitive way. Yr32 was detected in several wheats, including the North American differential tester Tres.

Disomic Thinopyrum intermedium addition lines in wheat with barley yellow dwarf virus resistance and with rust resistances.

Zhong 5 is a partial amphiploid (2n = 56) between Triticum aestivum (2n = 42) and Thinopyrum intermedium (2n = 42) carrying all the chromosomes of wheat and seven pairs of chromosomes from Th. intermedium. Following further backcrossing to wheat, six independent stable 2n = 44 lines were obtained representing 4 disomic chromosome addition lines. One chromosome confers barley yellow dwarf virus (BYDV) resistance, whereas two other chromosomes carry leaf and stem rust resistance; one of the latter also confers stripe rust resistance. Using RFLP and isozyme markers we have shown that the extra chromosome in the Zhong 5-derived BYDV resistant disomic addition lines (Z1, Z2, or Z6) belongs to the homoeologous group 2. It therefore carries a different locus to the BYDV resistant group 7 addition, L1, described previously. The leaf, stem, and stripe rust resistant line (Z4) carries an added group 7 chromosome. The line Z3 has neither BYDV nor rust resistance, is not a group 2 or group 7 addition, and is probably a group 1 addition. The line Z5 is leaf and stem rust resistant, is not stripe rust resistant, and its homoeology remains unknown.