R Genes Research Articles

Identification ofSr31andSr36stem rust resistance genes in wheat cultivars registered in Hungary

In Hungary, stem rust epidemics caused by Puccinia graminis f. sp. tritici are rare, but due to the severity of infection the stem rust fungus can pose a great hazard to wheat production. As new virulent races can appear, it is important for breeders to know of the genetic background of the stem rust resistance in their cultivars. In this study, 220 winter wheat cultivars registered in Hungary in the past 35 years were investigated using molecular markers to determine the presence or absence and frequency of the two important stem rust resistance genes Sr31 and Sr36. The results indicated that both Sr31 and Sr36 genes are widespread in wheat cultivars registered in Hungary. Sr31 was detected in 24.1% of these wheats, and Sr36 in 15.9%. These genes occurred to a somewhat larger extent in the 156 local cultivars: one-third (32.1%) had the Sr31 and 18.0% the Sr36 gene. Of these, 2 cultivars (1.3%) had both genes (Sr31+ Sr36). Among the 64 foreign cultivars only 3 (4.7%) carried the Sr31 gene. In the foreign group, Sr36 was only detected in the seven Croatian cultivars. Tests also revealed possible false pedigrees for some cultivars. Inoculation tests showed that both genes were still effective. One-sixth (16.7%) of stem rust resistant cultivars did not carry the target genes indicating the possible presence of other efficient Sr genes. Data may help breeders to incorporate effective Sr genes into new cultivars.

Recent occurrence ofPuccinia graminisf. sp.triticiin Italy: Pathogen virulence composition and seedling resistance of durum and common wheat

Regular disease monitoring is currently carried out in the most important Italian wheat growing areas. In 2007–08 stem rust was absent in all locations tested except Montelibretti (Rome, Central Italy), where two common wheat varieties “Arsenal” and “Compair” had stem rust infections. Two stem rust pathotypes were identified by testing in the greenhouse a set of differential lines/varieties carrying known genes for resistance to Puccinia graminis. These pathotypes corresponded to races MSK and PTK on the basis of the North American classification system. Genes Sr24 and Sr25 (both derived from Thinopyrum ponticum) and Sr31 (from Secale cereale), were resistant to the Italian pathotypes, and the lines carrying Sr38 (from Triticum ventricosum) were susceptible.Tests were carried out to determine the seedling stem rust response of durum and common wheat cultivars grown in Italy. Many durum wheat genotypes were resistant to MSK and PTK, while several common wheats were susceptible. The different response of th...

INFLUENCE OF SPATIAL AND TEMPORAL VARIATIONS IN THE HYPERSENSITIVE RESPONSE ON THE ACCUMULATION OF DEFENSE-RELATED TRANSCRIPTS IN POWDERY MILDEW-INFECTED BARLEY

Effective race-specific resistance genes (R-genes) against Blumeria graminis f. sp. hordei (Bgh) in barley determine spatial and temporal variation of the hypersensitive response (HR). This study investigated if different fast and slow acting HR, mediated by Mla R-genes in barley will influence the expression of nine commonly induced defense-response genes at time points that coincide with Bgh penetration and hyphal formation. Mla1 resistance was characterized by a fast and significant increase in the death of single Bgh-attacked epidermal cells in response to Bgh isolate C15, whereas Mla3 resistance was characterized by a slow increase in mesophyll multiple cell death in response to Bgh isolate A6. The reciprocal interactions result in compatible interactions. Using such experimental set-up, we partitioned the source of variation in gene expression and found that three genes were affected in a Bgh isolate-dependent manner, and five genes were affected in a host-dependent manner, regardless of the compatibility of the interaction. The results from this study show that the differential expression of many Bgh-responsive defense genes in barley does not necessarily correlate with the spatial and temporal variations in HR, but can be significantly influenced by: (i) the low genetic variability in the near isogenic lines or (ii) differences in the aggressiveness of pathogenic isolates. However, among the nine genes, expression of BAX inhibitor-1 (BI-1), correlated strongly with the timing of cellular events leading to HR in an interaction- specific manner, suggesting that BI-1 could be used as a HR marker in barley.

CHARACTERISATION OF RESISTANCE TO LEAF RUST IN AN INTERNATIONAL BREAD WHEAT NURSERY

Greenhouse seedling rust tests of the 35th International Bread Wheat Screening Nursery (IBWSN), distributed by the International Wheat and Maize Improvement Centre in 2002, demonstrated that 290 (58%) of the 500 entries likely carried the 1RS.1BL translocation, and therefore the rust resistance genes Lr26, Yr9 and Sr31. A selection of 109 lines identified as carrying this translocation was postulated to carry the major seedling resistance genes Lr3a, Lr13, Lr16, Lr19, Lr23, Lr24 and Lr27+Lr31 in addition to Lr26. The leaf rust seedling genes Lr13, Lr16 and Lr27+Lr31, were the most common seedling resistance genes in a selection of 100 lines lacking the 1RS.1BL translocation. While no new sources of seedling resistance to leaf rust were found in this study, and virulence is known for all of the seedling genes identified, 46 lines were identified that dispayed moderately high to very high levels of adult plant resistence (APR) to leaf rust in the field over 2 years that could be very useful in developing new wheat cultivars with resistance to Puccinia triticina. Of these, 24 were shown to carry Lr34, and based on pedigree analysis, it is expected that the APR gene Lr46 is also present in at least some lines. Genetic studies are needed to characterize the APR in these lines to assess their full value as sources of new leaf rust resistance.

Breeding of spring common wheat for resistance to local populations and the virulent race Ug99 of stem rust in West Siberia

Commercial cultivars, breeding material, and near-isogenic Sr gene lines of spring common wheat were tested for resistance to the Siberian population of stem rust races in an experimental field of the Omsk Agrarian University and to virulent race Ug99 at the Institute of Plant Pathology in Kenya (Africa). Resistant material was selected for breeding in West Siberia. The genetic value of populations developed by a shuttle breeding program among scientific institutions of Kazakhstan, West Siberia, and the International Maize and Wheat Improvement Center (CIMMYT), Mexico, is proven.

Alternative splicing variability: exactly how similar are two identical cells?

Alternative splicing variability: exactly how similar are two identical cells?

Erratum to: An accurate DNA marker assay for stem rust resistance gene Sr2 in wheat

Erratum to: An accurate DNA marker assay for stem rust resistance gene Sr2 in wheat

Conflicting mapping results for stem rust resistance gene Sr13

Theor Appl Genet (2011) 122:659 DOI 10.1007/s00122-010-1495-2 COMMENT Conflicting mapping results for stem rust resistance gene Sr13 J. Dubcovsky • F. Ordon • D. Perovic B. Admassu • W. Friedt • Z. Abate • W. Zhang • S. Chao Published online: 14 December 2010 O The Author(s) 2010. This article is published with open access at Springerlink.com Two manuscripts with conflicting results on the mapping location of stem rust resistance gene Sr13 in wheat are published in this issue of TAG (Admassu et al. and Simons et al.). Both resistance genes were mapped on the long arm of chromosome 6AL, but the gene mapped by Admassu et al. between markers barc37 and wmc256 is more than 50 cM proximal to the one mapped by Simons et al. between markers CD926040 and BE471213. After the publication of the two manuscripts in TAG online, the authors of both manuscripts became aware of the conflicting results and they exchanged the critical hexaploid wheat cytogenetic stocks Khapstein/9*LMPG (developed by Dr. D. Knott) and the recurrent parent LMPG to deter- mine the source of the differences. In addition, they requested seeds for these two stocks from the U.S. Cereal Disease Laboratory in Saint Paul Minnesota (Dr. Yue Jin) and from Canada Agri-Food, Winnipeg (Dr. Tom Fetch). The online version of the original articles can be found under doi:10.1007/s00122-010-1433-3 and 10.1007/s00122-010-1444-0. J. Dubcovsky (&) Z. Abate W. Zhang Department of Plant Sciences, University of California, Davis, CA 95616, USA e-mail: jdubcovsky@ucdavis.edu F. Ordon D. Perovic B. Admassu Julius Kuehn-Institute, Federal Research Institute for Cultivated Plants (JKI), Institute for Resistance Research and Stress Tolerance, Erwin-Baur-Str. 27, 06484 Quedlinburg, Germany W. Friedt Institute of Crop Science and Plant Breeding I, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany S. Chao USDA-ARS, Biosciences Research Laboratory, 1605 Albrecht Blvd N, Fargo, ND 58102-2765, USA Analysis of these stocks with molecular markers for the long arm of chromosome 6AL revealed that the Khapstein/ 9*LMPG seed stock used in the Admassu et al. paper was different from the other three Khapstein/9*LMPG stocks. Molecular markers barc37, barc107, barc118, barc1165, gwm570, wmc179, wmc256, wmc580, and cfd2 all showed different bands in the seed stock used in the Admassu paper relative to the seed stocks from the University of Califor- nia, the Cereal Disease Laboratory and Agri-Food Canada. These results indicate that the Khapstein/9*LMPG seed stock used in the Admassu paper is different from the other three. Since the Khapstein/9*LMPG hexaploid genetic stock defines the gene name Sr13, the gene mapped by Admassu et al. is most likely not Sr13 and should be renamed. The Khapstein/9*LMPG developed by Dr. D. Knott is polymorphic with the LMPG recurrent parent only for markers closely linked to the stem rust resistance gene mapped in the four tetraploid populations in the distal region of chromosome arm 6AL (barc104b and dupw167) by Simons et al. This observation, together with the fact that Sr13 was originated in tetraploid wheat (Khapli), provides indirect evidence that the gene mapped by Simons et al. is Sr13. Mapping the stem rust resistance gene present in the correct Khapstein/9*LMPG stock in an hexaploid segregating population will provide the final answer. Interestingly, both genes confer resistance to the new stem rust race Ug99 (TTKSK) suggesting that it would be possible to combine the two sources of resistance to Ug99 in the same 6AL arm. We have initiated crosses between the correct Khapstein/9*LMPG genetic stock and the source of the Admassu et al. Ug99 resistance to recombine both genes. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Effect of flavonoid pigments on the accumulation of fumonisin B1 in the maize kernel

Mycotoxins are secondary metabolites with potential dangers for animal and human health. In particular, maize (Zea mays L.) infection caused by Fusarium and the consequent fumonisin contamination is widespread in several countries such as Italy. We developed six maize populations differing in their constitution of regulatory genes able to accumulate respectively anthocyanins in the aleurone layer (r1 gene), pericarp (b1 and pl1 genes) and phlobaphene in the pericarp (p1 gene). These coloured populations, with the related control colourless populations were analysed for mycotoxin content in the kernels during three field seasons with the aim of understanding if there were any correlations with their ability to accumulate flavonoids in kernel tissues. Our results indicate that accumulation of flavonoid pigments in the seeds, in particular phlobaphenes, is able to reduce the level of fumonisin B1. This finding could be used to minimize kernel mycotoxin contamination in this crop, in particular, the development of sweet, pop and polenta coloured corn varieties will help the farmer to keep the level of fumonisin under the threshold of contamination established for human corn consumption.

An accurate DNA marker assay for stem rust resistance gene Sr2 in wheat

The stem rust resistance gene Sr2 has provided broad-spectrum protection against stem rust (Puccinia graminis Pers. f. sp. tritici) since its wide spread deployment in wheat from the 1940s. Because Sr2 confers partial resistance which is difficult to select under field conditions, a DNA marker is desirable that accurately predicts Sr2 in diverse wheat germplasm. Using DNA sequence derived from the vicinity of the Sr2 locus, we developed a cleaved amplified polymorphic sequence (CAPS) marker that is associated with the presence or absence of the gene in 115 of 122 (95%) diverse wheat lines. The marker genotype predicted the absence of the gene in 100% of lines which were considered to lack Sr2. Discrepancies were observed in lines that were predicted to carry Sr2 but failed to show the CAPS marker. Given the high level of accuracy observed, the marker provides breeders with a selection tool for one of the most important disease resistance genes of wheat.

Serine racemase deletion disrupts memory for order and alters cortical dendritic morphology

There is substantial evidence implicating N-methyl-D-aspartate receptors (NMDARs) in memory and cognition. It has also been suggested that NMDAR hypofunction might underlie the cognitive deficits observed in schizophrenia as morphological changes, including alterations in the dendritic architecture of pyramidal neurons in the prefrontal cortex (PFC), have been reported in the schizophrenic brain post mortem. Here, we used a genetic model of NMDAR hypofunction, a serine racemase knockout (SR-/-) mouse in which the first coding exon of the mouse SR gene has been deleted, to explore the role of D-serine in regulating cognitive functions as well as dendritic architecture. SR-/- mice exhibited a significantly disrupted representation of the order of events in distinct experiences as showed by object recognition and odor sequence tests; however, SR-/- animals were unimpaired in the detection of novel objects and in spatial displacement, and showed intact relational memory in a test of transitive inference. In addition, SR-/- mice exhibited normal sociability and preference for social novelty. Neurons in the medial PFC of SR-/- mice displayed reductions in the complexity, total length and spine density of apical dendrites. These findings show that D-serine is important for specific aspects of cognition, as well as in regulating dendritic morphology of pyramidal neurons in the medial PFC (mPFC). Moreover, they suggest that NMDAR hypofunction might, in part, be responsible for the cognitive deficits and synaptic changes associated with schizophrenia, and highlight this signaling pathway as a potential target for therapeutic intervention.

HISTOLOGICAL AND INITIAL MOLECULAR ANALYSIS OF UG99, THE SR31-BREAKING RACE OF THE WHEAT STEM RUST FUNGUS

The Sr31-virulent stem rust race Ug99 probably evolved from race UVPgt55 (Sr31-avirulent). To find differences between Ug99 and UVPgt55, both races were grown on two pairs of near-isogenic wheat lines with (Federation*4/Kavkaz and Thatcher-Sr31) and without the Sr31 gene for resistance (cvs Federation and Thatcher). Five days post inoculation, a difference in growth of Ug99 and UVPgt55 became obvious on Federation* 4/Kavkaz: while growth of UVPgt55 was inhibited, Ug99 grew well. In contrast, Thatcher-Sr31 inhibited the growth of both races, hinting at an additional resistance gene in this line not broken by Ug99. Furthermore, mycelia of both races were successfully grown in axenic culture to isolate genomic DNA of high purity. Inverse sequence-tagged repeat and random amplified polymorphic DNA analyses showed almost identical patterns in both races which clearly differed from the patterns of the Canadian stem rust race 32. Two SSHdifferential cDNA libraries were constructed, one representing mainly genes of Ug99 active in planta, the other genes of UVPgt55. Reciprocal hybridisations of cDNA macro-arrays corroborated the strong similarity between the two races, but some differentially expressed genes were found. Sixty-five clones of Ug99 and 91 clones of UVPgt55 were sequenced. Among these, five genes of UVPgt55 with a secretory signal peptide coding for proteins of unknown function were identified as potential avirulence genes.

The transformer gene of Ceratitis capitata: a paradigm for a conserved epigenetic master regulator of sex determination in insects

The transformer gene in Ceratitis capitata (Cctra(ep)) is the founding member of a family of related SR genes that appear to act as the master epigenetic switch in sex determination in insects. A functional protein seems to be produced only in individuals with a female XX karyotype where it is required to maintain the productive mode of expression through a positive feedback loop and to direct female development by instructing the downstream target genes accordingly. When zygotic activation of this loop is prevented, male development follows. Recently, tra(ep) orthologues were isolated in more distantly related dipteran species including Musca domestica, Glossina morsitans and Lucilia cuprina and in the Hymenopterans Apis mellifera and Nasonia vitripennis. All of these tra(ep) orthologues seem to act as binary switches that govern all aspects of sexual development. Transient silencing leads to complete masculinization of individuals with a female karyotype. Reciprocally, in some systems it has been shown that transient expression of the functional TRA product is sufficient to transactivate the endogenous gene and implement female development in individuals with a male karyotype. Hence, a mechanism based on tra(ep) epigenetic autoregulation seems to represent a common and presumably ancestral single principle of sex determination in Insecta. The results of these studies will not only be important for understanding divergent evolution of basic developmental processes but also for designing new strategies to improve genetic sexing in different insect species of economical or medical importance.

DNA markers of the R1 and R3 genes as predictors of potato late blight resistance

To investigate whether the presence of R-genes is associated with higher late blight resistance of potato cultivars, we modified an earlier described SCAR marker for the R1 gene and developed a new SCAR marker for the R3 gene. We demonstrated the significant input of R1 transferred from Solanum demissum and probably S. stoloniferum into foliage and tuber resistance; the effect of R3 introgression was less conclusive.

Genetic mapping of the stem rust (Puccinia graminis f. sp. tritici Eriks. & E. Henn) resistance gene Sr13 in wheat (Triticum aestivum L.)

Puccinia graminis f. sp. tritici, the causative agent of stem rust in wheat, is known for its high virulence variability and ability to evolve new virulence to resistance genes. Thus, pyramiding of several resistance genes in a single line is the best strategy for a sustainable control of wheat stem rust. Sr13 is one of the few resistance genes that are effective against wide ranging P. graminis f. sp. tritici races, including the pestilent race Ug99. Its effectiveness to Ug99 makes it a valuable source for resistance to stem rust. Molecular markers play a pivotal role in the genetic characterization of the new sources of resistance as well as in stacking two or more resistance genes in a single line. Therefore, the aim of this study was to develop molecular markers for Sr13 facilitating efficient pyramiding of Sr genes. Based on the 158 F(2) individuals derived from a cross of Khapstein/9*LMPG×Morocco and SSR analyses, the Sr13 locus was mapped on chromosome 6A of wheat, and a genetic map comprising about 90cM was constructed with the closest marker barc37 being located 4.0cM distally of Sr13. Of the nine mapped markers, barc37 amplified an allele specific for the presence of Sr13 as shown by testing different cultivars and breeding lines. These newly developed markers will increase the efficiency of incorporating Sr13 into cultivars that are widely adopted, but susceptible to hazardous Ug99 and/or assist for the development of new elite lines that are resistant to Ug99.

Identification of Flanking Markers for the Stem Rust Resistance Gene Sr6 in Wheat

ABSTRACTThe wheat (Triticum aestivum L. and T. turgidum L.) stem rust resistance gene Sr6 confers a high level of resistance against a wide range of races of Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. and E. Henn. in North America. In this study, we report the identification of flanking markers for Sr6. We used a population of 139 recombinant inbred lines from the cross MN99394 × MN98550. A partial linkage map of chromosome 2D comprised Xgwm484, Xcfd77, Xcfd43, Xwmc453, Sr6, XwPt_4381, XwPt_0330, Xgpw94049, and Xgwm102. Four markers mapped distal to Sr6, while the other four were proximal within distances of 4.8 and 6.5 cM, respectively. Marker‐assisted selection and pyramiding of Sr6 with other stem rust resistance genes could benefit from the availability of Sr6‐flanking markers.

Development of Wheat Lines Having a Small Introgressed Segment Carrying Stem Rust Resistance Gene Sr22

ABSTRACTThe wheat stem rust resistance gene Sr22 confers resistance to Puccinia graminis f. sp. tritici Pers. race TTKSK (also known as Ug99) that developed in Africa and is an immediate threat to world wheat production. The resistance gene is present on a chromosomal translocation derived from Triticum boeoticum Boiss., which has a genome that is partially homologous to the A genome of T. aestivum L. Sr22 has been deployed in a limited number of cultivars due to poor agronomic performance of lines carrying the resistance gene. Linkage analysis of simple sequence repeat (SSR) markers on chromosome 7A was performed to identify loci closely linked to Sr22. The most tightly linked proximal and distal SSR marker loci were Xcfa2123 and Xwmc633, respectively. A two‐step process was then used to develop resistant lines having smaller chromosome segments derived from the diploid donor. First, individuals in which a single recombination event had occurred between wheat and the Sr22 introgression were identified in the mapping populations. In spite of reduced recombination between T. boeoticum and T. aestivum chromosomes, sufficient recombination events were found among 398 F3:4 lines derived from recombinant F2 progeny to recover multiple resistant individuals with smaller alien introgressions. Resistant lines were identified having less than 6% of the chromosome arm derived from T. boeoticum. These lines may provide a more agronomically desirable source of Sr22 that can be readily deployed in cultivars resistant to Ug99.

Genetics and mapping of seedling resistance to Ug99 stem rust in Canadian wheat cultivars ‘Peace’ and ‘AC Cadillac’

Stem rust (caused by Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.) has re-emerged as a threat to wheat production with the evolution of new pathogen races, namely TTKSK (Ug99) and its variants, in Africa. Deployment of resistant wheat cultivars has provided long-term control of stem rust. Identification of new resistance genes will contribute to future cultivars with broad resistance to stem rust. The related Canadian cultivars Peace and AC Cadillac show resistance to Ug99 at the seedling stage and in the field. The purpose of this study was to elucidate the inheritance and genetically map resistance to Ug99 in these two cultivars. Two populations were produced, an F(2:3) population from LMPG/AC Cadillac and a doubled haploid (DH) population from RL6071/Peace. Both populations showed segregation at the seedling stage for a single stem rust resistance (Sr) gene, temporarily named SrCad. SrCad was mapped to chromosome 6DS in both populations with microsatellite markers and a marker (FSD_RSA) that is tightly linked to the common bunt resistance gene Bt10. FSD_RSA was the closest marker to SrCad (≈ 1.6 cM). Evaluation of the RL6071/Peace DH population and a second DH population, AC Karma/87E03-S2B1, in Kenya showed that the combination of SrCad and leaf rust resistance gene Lr34 provided a high level of resistance to Ug99-type races in the field, whereas in the absence of Lr34 SrCad conferred moderate resistance. A survey confirmed that SrCad is the basis for all of the seedling resistance to Ug99 in Canadian wheat cultivars. While further study is needed to determine the relationship between SrCad and other Sr genes on chromosome 6DS, SrCad represents a valuable genetic resource for producing stem rust resistant wheat cultivars.

A robust molecular marker for the detection of shortened introgressed segment carrying the stem rust resistance gene Sr22 in common wheat

Stem rust resistance gene Sr22 transferred to common wheat from Triticum boeoticum and T. monococcum remains effective against commercially prevalent pathotypes of Puccinia graminis f. sp. tritici, including Ug99 and its derivatives. Sr22 was previously located on the long arm of chromosome 7A. Several backcross derivatives (hexaploid) possessing variable sized Sr22-carrying segments were used in this study to identify a closely linked DNA marker. Expressed sequenced tags belonging to the deletion bin 7AL-0.74-0.86, corresponding to the genomic location of Sr22 were screened for polymorphism. In addition, RFLP markers that mapped to this region were targeted. Initial screening was performed on the resistant and susceptible DNA bulks obtained from backcross derivatives carrying Sr22 in three genetic backgrounds with short T. boeoticum segments. A cloned wheat genomic fragment, csIH81, that detected RFLPs between the resistant and susceptible bulks, was converted into a sequence tagged site (STS) marker, named cssu22. Validation was performed on Sr22 carrying backcross-derivatives in fourteen genetic backgrounds and other genotypes used for marker development. Marker cssu22 distinguished all backcross-derivatives from their respective recurrent parents and co-segregated with Sr22 in a Schomburgk (+Sr22)/Yarralinka (-Sr22)-derived recombinant inbred line (RIL) population. Sr22 was also validated in a second population, Sr22TB/Lakin-derived F(4) selected families, containing shortened introgressed segments that showed recombination with previously reported flanking microsatellite markers.

Potato R1 resistance gene confers resistance against Phytophthora infestans in transgenic tomato plants

Tomato is challenged by several pathogens which cause loss of production. One such pathogen is the oomycete Phytophthora infestans which is able to attack all the aerial parts of the plant. Although a wide range of resistance sources are available, genetic control of this disease is not yet successful. Pyramiding R-genes through genetic transformation could be a straightforward way to produce tomato and potato lines carrying durable resistance to P. infestans. In this work the R1 potato gene was transferred into tomato lines. The tomato transgenic lines were analyzed by using q-RT-PCR and progeny segregation to determine the gene copy number. To test the hypothesis that R1 represents a specifically regulated R-gene, transgenic tomato plants were inoculated with P. infestans isolate 88133 and IPO. All the plants containing the R1 gene were resistant to the late blight isolate IPO-0 and susceptible to isolate 88133. These results provide evidence for specific activation of the R1 gene during pathogen challenge. Furthermore, evidence for enhancement of PR-1 gene expression during P. infestans resistance response was obtained.