Sugarcane Mosaic Virus Resistance Research Articles

Small RNA and Degradome Deep Sequencing Reveal Regulatory Roles of MicroRNAs in Response to Sugarcane Mosaic Virus Infection on Two Contrasting Sugarcane Cultivars.

MicroRNAs (miRNAs) play an essential regulatory role in plant-virus interaction. However, few studies have focused on the roles of miRNAs and their targets after sugarcane mosaic virus (SCMV) infection in sugarcane. To address this issue, we conducted small RNA (sRNA) and degradome sequencing on two contrasting sugarcanes (SCMV-resistant 'Fuoguo1' [FG1] and susceptible 'Badila') infected by SCMV at five time points. A total of 1,578 miRNAs were profiled from 30 sRNA libraries, comprising 660 known miRNAs and 380 novel miRNAs. Differential expression analysis of miRNAs revealed that most were highly expressed during the SCMV exponential phase in Badila at 18 h postinfection, with expression profiles positively correlated with virus replication dynamics as observed through clustering. Analysis of degradome data indicated a higher number of differential miRNA targets in Badila compared to FG1 at 18 h postinfection. Gene ontology (GO) enrichment analysis significantly enriched the stimulus-response pathway, suggesting negative regulatory roles to SCMV resistance. Specifically, miR160 upregulated expression patterns and validated in Badila through quantitative real-time PCR (qRT-PCR) in the early stages of SCMV multiplication. Our research provides new insights into the dynamic response of plant miRNA and virus replication and contributes valuable information on the intricate interplay between miRNAs and SCMV infection dynamics. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Effects of Maize Chlorotic Mottle Virus and Potyvirus Resistance on Maize Lethal Necrosis Disease.

Maize lethal necrosis (MLN) is a viral disease caused by host co-infection by maize chlorotic mottle virus (MCMV) and a potyvirus, such as sugarcane mosaic virus (SCMV). The disease is most effectively managed by growing MLN-resistant varieties. However, the relative importance of MCMV and potyvirus resistance in managing this synergistic disease is poorly characterized. In this study, we evaluated the effects of SCMV and/or MCMV resistance on disease, virus titers, and synergism and explored expression patterns of known potyvirus resistance genes TrxH and ABP1. MLN disease was significantly lower in both the MCMV-resistant and SCMV-resistant inbred lines compared with the susceptible control Oh28. Prior to 14 days postinoculation (dpi), MCMV titers in resistant lines N211 and KS23-6 were more than 100,000-fold lower than found in the susceptible Oh28. However, despite no visible symptoms, titer differences between MCMV-resistant and -susceptible lines were negligible by 14 dpi. In contrast, systemic SCMV titers in the potyvirus-resistant line, Pa405, ranged from 130,000-fold to 2 million-fold lower than susceptible Oh28 as disease progressed. Initial TrxH expression was up to 49,000-fold lower in Oh28 compared with other genotypes, whereas expression of ABP1 was up to 4.5-fold lower. Measures of virus synergy indicate that whereas MCMV resistance is effective in early infection, strong potyvirus resistance is critical for reducing synergist effects of co-infection on MCMV titer. These results emphasize the importance of both potyvirus resistance and MCMV resistance in an effective breeding program for MLN management.

Multiomic investigation of Sugarcane mosaic virus resistance in sugarcane

Sugarcane mosaic virus (SCMV) is the main etiological agent of sugarcane mosaic disease, which affects sugarcane and other grass crops. Despite the extensive characterization of quantitative trait loci controlling resistance to SCMV in maize, the genetic basis of this trait in sugarcane is largely unexplored. Here, a genome-wide association study was performed and machine learning coupled with feature selection was used for genomic prediction of resistance to SCMV in a diverse sugarcane panel. Nine single-nucleotide polymorphisms (SNPs) explained up to 29.9% of the observed phenotypic variance and a 73-SNP set predicted resistance with high accuracy, precision, recall, and F1 scores (the harmonic mean of precision and recall). Both marker sets were validated in additional sugarcane genotypes, in which the SNPs explained up to 23.6% of the phenotypic variation and predicted resistance with a maximum accuracy of 69.1%. Synteny analyses suggested that the gene responsible for the majority of SCMV resistance in maize is absent in sugarcane, explaining why this major resistance source has not been identified in this crop. Finally, using sugarcane RNA-Seq data, markers associated with resistance to SCMV were annotated, and a gene coexpression network was constructed to identify the predicted biological processes involved in resistance. This network allowed the identification of candidate resistance genes and confirmed the involvement of stress responses, photosynthesis, and the regulation of transcription and translation in resistance to SCMV. These results provide a practical marker-assisted breeding approach for sugarcane and identify target genes for future studies of SCMV resistance.

Assessment of Genetic Variability in Sugarcane (Saccharum officinarum L.) Genotypes for Better Yield, Quality and Sugarcane Mosaic Virus Resistance in Central Punjab, Pakistan

Assessment of Genetic Variability in Sugarcane (Saccharum officinarum L.) Genotypes for Better Yield, Quality and Sugarcane Mosaic Virus Resistance in Central Punjab, Pakistan

Sugarcane Mosaic Virus Resistance in the Wisconsin Sweet Corn Diversity Panel

Sugarcane mosaic virus [SCMV (Potyvirus sugarcane mosaic virus)] is an ssRNA virus that negatively affects yield in maize (Zea mays) worldwide. Resistance to SCMV is controlled primarily by a single dominant gene (Scm1). The goal of this study was to identify sweet corn (Z. mays) inbreds that demonstrate resistance to SCMV, confirm the presence of genomic regions previously identified in maize associated with resistance, and identify other resistant loci in sweet corn. Eight plants from each of 563 primarily sweet corn inbred lines were tested for SCMV resistance. Plants were inoculated 14 d after planting and observed for signs of infection 24 d after planting. A subset of 420 inbred lines were genotyped using 7504 high-quality genotyping-by-sequencing single-nucleotide polymorphism markers. Population structure of the panel was observed, and a genome-wide association study was conducted to identify loci associated with SCMV resistance. Forty-six of the inbreds were found to be resistant to SCMV 10 d after inoculation. The Scm1 locus was confirmed with the presence of two significant loci on chromosome 6 (P = 2.5 × 10−8 and 1.6 × 10−8), 5 Mb downstream of the Scm1 gene previously located at Chr6: 14194429.14198587 and the surrounding 2.7-Mb presence–absence variation. We did not identify other loci associated with resistance. This research has increased information on publicly available SCMV-resistant germplasm useful to future breeding projects and demonstrated that SCMV resistance in this sweet corn panel is driven by the Scm1 gene.

MAJOR EFFECT QTL ON CHROMOSOME 3 CONFERRING MAIZE RESISTANCE TO SUGARCANE MOSAIC VIRUS

The Sugarcane mosaic virus (SCMV), a maize pathogen epidemic worldwide, is the causal agent of common mosaic, one of the most important viral diseases in Brazil. In this study, we mapped and characterized quantitative trait loci (QTL) conferring resistance to SCMV in a maize population consisting of 127 F2:3 families from the cross between two Brazilian maize inbred lines, L18 (resistant) × L19 (susceptible). Field trials were carried out in two years to evaluate the F2:3 families according to a resistance score after artificial inoculation. QTLs were detected via composite interval mapping, using a linkage map based on 82 SSRs, 3 CAPS and 296 SNPs. The heritability ranged from 73.68 to 95.16% and SCMV resistance QTLs were consistently identified on chromosomes 1 and 3, showing minor and major effects, respectively. The major QTL on chromosome 3 explained a large proportion of the genetic variance, being 50 and 70% in year 1 and 2, respectively, while the minor QTL on chromosome 1 explained 11 and 8% in year 1 and 2, respectively. The SNP marker co-localized with the major QTL peak on chromosome 3 and its right flanking marker are positioned inside the predicted gene GRMZM2G122443 encoding a glucosidase II, and the left flanking marker inside the GRMZM2G140537 that encodes a protein tyrosine kinase. Moreover, within this QTL region there are also the GRMZM2G160902 and GRMZM2G122481 predicted genes, encoding a bZIP transcription factor and a cytochrome C oxidase, respectively. The colocalization with this major effect QTL suggests a putative involvement of these candidate genes with maize responses to SCMV resistance, but further functional studies are required for such validation. Our results provide resistance source and genomic target for marker-assisted breeding aiming the development of maize resistant cultivars to SCMV.

Selecting for Coupling Phase Recombination between Potyvirus Resitance and White Endosperm Colour in Maize Preferred by Farmers in Sub-Saharan Africa (SSA)


 
 
 Maize lethal necrosis (MLN) disease caused by a combined infection of Maize chlorotic mottle virus (MCMV) and any cereal infecting potyvirus is a threat to food security in Sub-Saharan Africa (SSA). Resistance to potyvirus has been extensively studied and Mdm1 gene for potyvirus resistance on chromosome 6 of maize is linked to Y1 gene for maize endosperm colour. This study is aimed at se- lecting for coupling-phase recombination of potyvirus resistance and white endosperm colour. White susceptible maize lines CML333 and CML277 were crossed with a yellow resistant line, Pa405, to produce F1 and F2 progenies. Progenies were screened using molecular markers to recover 22 white endosperm recombinants. 22 selections were advanced to F3 recombinant families, and 10 were as- sayed for their responses to Maize dwarf mosaic virus (MDMV) and Sugarcane mosaic virus (SCMV). Four families segregated for SCMV resistance, selection of homozygous recombinants within these families will provide lines appropriate for improving lines with resistance to SCMV and MLN resistance in SSA.
 KEY WORDS: MAIZE LETHAL NECROSIS (MLN), WHITE MAIZE, POTYVIRUS RESISTANCE, GENETIC RECOMBINATION, SUB-SAHARAN AFRICA.
 
 

Selecting for Coupling-Phase Recombination Between Potyvirus Resistance and White Endosperm Colour in Maize Preferred by Farmers in Sub-Saharan Africa (SSA)

Maize lethal necrosis (MLN) disease caused by a combined infection of Maize chlorotic mottle virus (MCMV) and any cereal infecting potyvirus is a threat to food security in Sub-Saharan Africa (SSA). Resistance to potyvirus has been extensively studied and Mdm1 gene for potyvirus resistance on chromosome 6 of maize is linked to Y1 gene for maize endosperm colour. This study is aimed at selecting for coupling-phase recombination of potyvirus resistance and white endosperm colour. White susceptible maize lines CML333 and CML277 were crossed with a yellow resistant line, Pa405, to produce F1 and F2 progenies. Progenies were screened using molecular markers to recover 22 white endosperm recombinants. 22 selections were advanced to F3 recombinant families, and 10 were assayed for their responses to Maize dwarf mosaic virus (MDMV) and Sugarcane mosaic virus (SCMV). Four families segregated for SCMV resistance, selection of homozygous recombinants within these families will provide lines appropriate for improving lines with resistance to SCMV and MLN resistance in SSA.

Somaclonal variations for red rot and sugarcane mosaic virus resistance and candidate genes integrity assessment in somaclones of selected sugarcane varieties (Saccharum officinarum L.)

Sugarcane is a complex allopolyploid hybrid with erratic flowering due to various geo -climatic factors hence deliberate hybridization for varietal improvement is a dilemma in most of the countries where sugarcane is cultivated. Somaclonal variations is an alternate strategy used for development of disease resistance and improvement in yield attributes, but point mutation in candidate genes is questionable. The aim of this study was to develop somaclones resistant to red rot and Sugarcane mosaic virus (SCMV) in obsolete sugarcane varieties and their genetic integrity assessment in candidate gene's exon regions. A total of 581 somaclones were developed, of which 201 survived after hardening and 121 after transplantation and screened against red rot and SCMV. Only 10% somaclones were found resistant to red rot in susceptible and moderately susceptible varieties while SCMV concentration was recorded less than negative control in somaclones. Four candidate genes namely; catalase (CAT1), sucrose phosphate synthase (SPS), gibberellin 2-xidase 4 (GA 2-oxidase 4) and tillering branched 1 (TB1) were evaluated for possible SNPs in their exon regions. Sequences of five representative somaclones were aligned with their parental clones and no possible SNP changes were observed. Somaclonal variations was a good source of genetic improvement of sugarcane for disease resistance with no SNP changes in candidate genes.

Genetic Analysis of Sugarcane mosaic virus Resistance in the Wisconsin Diversity Panel of Maize

Sugarcane mosaic virus (SCMV) and Maize dwarf mosaic virus can cause yield loss in maize (Zea mays L.). Previous studies identified two key genomic regions controlling host resistance: Scmv1 on chromosome 6 and Scmv2 on chromosome 3. In this study a diverse set of 578 inbreds adapted to a northern US Corn Belt environment, was inoculated at the three‐leaf stage with SCMV and rated for presence of virus symptoms at 7, 10, 14, 21, 28, and 35 d after inoculation. Scmv1 was present in all resistant inbreds. A single‐nucleotide polymorphism associated with SCMV resistance was found 5 Mb downstream of the putative location of Scmv1, and resistance at this downstream locus was correlated with a group of inbreds containing the presence allele of a 2.7‐Mb presence–absence variation (PAV) in the region encompassing Scmv1. The Scmv2 region was associated with resistance 35 d after inoculation only among the inbreds containing the presence allele, including Scmv1. Several other loci unlinked to Scmv1 and Scmv2 were associated with resistance in this panel, providing evidence for multigenic modification of the efficacy of Scmv1 and Scmv2. Sixty‐nine inbreds representing haplotype variation in the region surrounding Scmv1 on chromosome 6 were inoculated with SCMV at the three‐ and six‐leaf stage. Symptom development was reduced when inoculation was delayed to the six‐leaf stage, but 24 inbreds became fully symptomatic after 35 d regardless of the growth stage at inoculation. Inbreds with the presence allele of the PAV encompassing Scmv1 were more resistant to SCMV when inoculation was delayed to the six‐leaf stage than those that had the absence allele. Inbreds with the absence allele were susceptible regardless of growth stage at inoculation.

Characterization of Sugarcane Mosaic Virus Scmv1 and Scmv2 Resistance Regions by Regional Association Analysis in Maize.

Sugarcane Mosaic Virus (SCMV) causes one of the most severe virus diseases in maize worldwide, resulting in reduced grain and forage yield in susceptible cultivars. In this study, two association panels consisting of 94 inbred lines each, from China and the U.S., were characterized for resistance to two isolates: SCMV-Seehausen and SCMV-BJ. The population structure of both association panels was analyzed using 3072 single nucleotide polymorphism (SNP) markers. The Chinese and the U.S. panel were both subdivided into two sub-populations, the latter comprised of Stiff Stalk Synthetic (SS) lines and Non Stiff Stalk Synthetic (NSS). The relative kinships were calculated using informative 2947 SNPs with minor allele frequency ≥ 5% and missing data ≤ 20% for the Chinese panel and 2841 SNPs with the same characteristics were used for the U.S. panel. The Scmv1 region was genotyped using 7 single sequence repeat (SSR) and sequence-tagged site (STS) markers, and 12 SSR markers were used for the Scmv2 region in the U.S. panel, while 5 of them were used for the Chinese panel. For all traits, a MLM (Mix Linear Model) controlling both population structure and relative kinship (Q + K) was used for association analysis. Three markers Trx-1, STS-11, and STS-12 located in the Scmv1 region were strongly associated (P = 0.001) with SCMV resistance, and explained more than 16.0%, 10.6%, and 19.7% of phenotypic variation, respectively. 207FG003 located in the Scmv2 region was significantly associated (P = 0.001) with SCMV resistance, and explained around 18.5% of phenotypic variation.

Genetic and Symptomatic Characterization of Sugarcane mosaic virus (SCMV) in Cuba

Sugarcane mosaic resistance is established as a key criterion for the breeding program in Cuba. However, molecular characterization of Sugarcane mosaic virus (SCMV) strains occurring in Cuba has not been reported so far. Leaf samples from commercial sugarcane cultivars were collected for SCMV screening in three testing sites (the Matanzas, Camaguey and Holguin provinces). Reverse-Transcriptase polymerase chain reaction was used to identify the virus. The nucleotide sequence comparison grouped the isolates into SCMV subgroups. Sugarcane cultivars inoculated with SCMV from three testing sites displayed different symptoms. Results should be decisive to generate the highest selection pressure, increasing the efficiency of the sugarcane breeding program to the SCMV resistance in the commercial cultivars.

Application of RNA interference methodology to investigate and develop SCMV resistance in maize.

Specific fragments of the sugarcane mosaic virus (SCMV) coat protein gene (cp) were amplified by reverse transcriptionpolymerase chain reaction and used to construct a marker free small interfering RNA complex expression vector against SCMV. In planta transformation was performed on maize (Zea mays) inbred line 8112 mediated by Agrobacterium tumefaciens. PCR and Southern blot analyses demonstrated successful integration of the cp segment into the 8112 genome. The in planta transformation frequency was 0.1%, and the cotransformed frequency with the cp and bar genes was 0.034%. Real-time quantitative PCR of samples from different transgenic plant organs showed that the expression of the cp gene fragment in transgenic plants was variable and that the highest expression level occurred in the tassels and leaves and the lowest expression occurred in the roots. Real-time quantitative PCR was also used to measure how gene expression in transgenic T2 generation plants inoculated with SCMV changes over time. The results showed that the hairpin RNA structure transcribed from the cp gene interfered with SCMV infection and transgenic maize lines were not equally effective in preventing SCMV infection. Our findings provide a valuable tool for controlling plant viruses using RNA interference and the posttranslational gene silencing approach.

Sugarcane Transcript Profiling Assessed by cDNA-AFLP Analysis during the Interaction with <i>Sugarcane Mosaic Virus</i>

Sugarcane mosaic caused by Sugarcane Mosaic Virus (SCMV) is one of the most important virus diseases of sugarcane. In the present study, changes in the transcription profile obtained by cDNA-AFLP analysis were investigated in two sugarcane varieties contrasting to SCMV resistance, when challenged with a severe virus strain. Healthy plants derived from meristem tip tissue culture were mechanically inoculated under greenhouse controlled conditions and sampled at 24, 48 and 72 hours after inoculation. A total of 392 transcript-derived fragments (TDFs) were verified in the resistant variety against 380 in the susceptible one. The two sugarcane genotypes showed differential behavior in the number of induced and repressed TDFs along the time-course samplings. Ten out of 23 sequenced TDFs (unique from the resistance variety), showed identity with known plant sequences, mostly related to plant defense mechanisms against pathogens. The cDNA-AFLP technique was effective in revealing changes in the transcription profile within and between contrasting varieties when challenged by SCMV.

Comparative proteomic analysis of the plant–virus interaction in resistant and susceptible ecotypes of maize infected with sugarcane mosaic virus

Sugarcane mosaic virus (SCMV) is an important viral pathogen and has caused serious losses in grain and forage yield. To identify candidate SCMV resistance proteins and to explore the molecular mechanisms involved in the plant-SCMV interaction, we conducted proteomic analyses of leaf samples from resistant and susceptible ecotypes of maize infected with SCMV. Proteins were analyzed by quantitative two-dimensional differential gel electrophoresis (2D-DIGE), and 93 protein spots showed statistically significant differences after virus inoculation. Functional categorization showed that SCMV-responsive proteins were mainly involved in energy and metabolism, stress and defense responses, photosynthesis, and carbon fixation. The majority of the identified proteins were located in chloroplast and cytoplasm based on bioinformatic analysis. Among these identified proteins, 17 have not been identified previously as virus-responsive proteins, and 7 were new and did not have assigned functions. Western blotting analyses confirmed the expression patterns of proteins of specific interest, and the genes encoding these proteins were further analyzed by real-time PCR. The results of this study showed overlapping and specific proteomic responses to SCMV infection between resistant and susceptible maize ecotypes. This study provides further insight into the molecular events during compatible and incompatible interactions between viruses and host plants. Sugarcane mosaic virus (SCMV) is an important viral pathogen and has caused serious losses in grain and forage yield. However, little is known about host-SCMV interactions from the proteome perspective. This study analyzed proteomic changes in resistant and susceptible plants that are infected with SCMV using DIGE based proteomics. We identified 17 proteins that have not been identified previously as virus-responsive proteins, and 7 new proteins without assigned functions. These proteins are interesting candidates for future research, as they may be associated with new biological functions and play important roles in plant-virus interactions. Real-time RT-PCR analysis of genes encoding several proteins of interest provided indication on whether the changes in protein abundance were regulated at the mRNA level. The results of this study showed overlapping and specific proteomic responses to SCMV infection between resistant and susceptible ecotypes. After inoculation, the proteins involved in energy and metabolism, stress and defense responses, photosynthesis and other four functional groups showed significant changes in both ecotypes, which suggested that SCMV infection influenced these physiological processes in both the resistant Siyi and the susceptible Mo17. However, the oxidative burst was more pronounced during incompatible plant-SCMV interactions, as compared to those defined as compatible. We also observed an increase of enzymes involved in glycolysis and gluconeogenesis pathways in the resistant maize ecotype Siyi, while decrease in the susceptible maize ecotype Mo17. In addition, there is a marked increase of guanine nucleotide-binding protein beta submit in the resistant Siyi, which suggests a possible involvement of G-protein associated pathways in the resistant responses of maize to SCMV. These observations may possibly reveal protein targets/markers that are useful in the design of future diagnosis or plant protection strategies and provide new insights into the molecular mechanism of plant-virus interactions.

Detection of Somaclonal Variation in Micropropagated Plants of Sugarcane and SCMV Screening through ELISA

Callogenesis is a helping tool in tissue culture for creating variation. The study was carried out to investigate the response of different sugarcane varieties to callogenesis in order to analyze variation for sugarcane mosaic virus resistance. Three sugarcane accessions viz HSF-242, S2003-US-623, and S2003-US-633 were used in this study. The genotypes showed high value of callus score ranging from 2.59 to 3.25. Genotype HSF-242 was highest callus producer with an average score of 3.25. Three different media were used for organogenesis. S2003-US-633 proved to be the most responsive to organogenesis with an average of 43.33%. Material was exposed to shooting and rooting media and somaclones were shifted to green house. The somaclones produced were screened for sugarcane mosaic virus by ELISA (enzyme linked immunosorbent assay). Among 10 parent plants and 32 somaclones of HSF-242, only four somaclones showed susceptibility to SCMV disease while seven (7) parents showed positive reaction to the disease. Somaclones produced were also analyzed by microsattelite molecular markers to check the variation between parents and somaclones produced at molecular level. Molecular markers are useful for assessment of variation and phylogenetic relationships. Out of thirty (30) fragments amplified with fifteen (15) primers used among the sugarcane somaclones and parents, eleven (11) bands were polymorphic while rest of the nineteen (19) bands were monomorphic. Therefore, it may be concluded from the present results that SSRs can be used for identification of somaclonal variation and the relationship between parents and Somaclones.

Molecular mapping of quantitative trait loci (QTLs) determining resistance to Sugarcane mosaic virus in maize using simple sequence repeat (SSR) markers

Molecular marker technology was used to map quantitative trait loci (QTLs) associated with resistance to Sugarcane mosaic virus (SCMV). This disease is spread worldwide and can cause devastating yield losses in susceptible maize cultivars. The aim of this study was to estimate genetic determination of resistance to SCMV in a maize population consisting of 120 F3 lines from a cross between maize inbred lines TR56 (susceptible) and TR42 (resistant). This population was evaluated for SCMV resistance in replicated greenhouse trials under artificial inoculation. The method of composite interval mapping (CIM) was employed for QTL analysis. Two genes were mapped on chromosome 6 using simple sequence repeat (SSR) and bulked segregant analyses (BSA), and a gene on chromosome 3 was found to be not significant. The resistance gene Scm1a on chromosome 6 (bin 6.00/6.01) was flanked by microsatellite markers bnlg1043 and phi126 with genetic distances of 1.0 and 0.6 cM, respectively whereas the genetic distances between two flanking markers bnlg1371 and bnlg1600 and the resistance gene Scm1b were 1.0 and 1.1 cM, respectively. Other SSRs from chromosomes 1, 5 and 10 detected no QTL using single marker analysis.

Responses of maize (Zea mays L.) near isogenic lines carrying Wsm1, Wsm2, and Wsm3 to three viruses in the Potyviridae

Genes on chromosomes six (Wsm1), three (Wsm2) and ten (Wsm3) in the maize (Zea mays L.) inbred line Pa405 control resistance to Wheat streak mosaic virus (WSMV), and the same or closely linked genes control resistance to Maize dwarf mosaic virus (MDMV) and Sugarcane mosaic virus (SCMV). Near isogenic lines (NIL) carrying one or two of the genes were developed by introgressing regions of the respective chromosomes into the susceptible line Oh28 and tested for their responses to WSMV, MDMV, and SCMV in the field and greenhouse. F(1) progeny from NIL × Oh28 were also tested. Wsm1, or closely linked genes, provided resistance to all three viruses, as determined by symptom incidence and severity. Wsm2 and Wsm3 provided resistance to WSMV. Wsm2 and/or Wsm3 provided no resistance to MDMV, but significantly increased resistance in plants with one Wsm1 allele. NIL carrying Wsm1, Wsm2, or Wsm3 had similar SCMV resistance in the field, but NIL with Wsm2 and Wsm3 were not resistant in the greenhouse. Addition of Wsm2 to Wsm1 increased SCMV resistance in the field. For all viruses, symptom incidence was higher in the greenhouse than in the field, and relative disease severity was higher in the greenhouse for WSMV and MDMV. An Italian MDMV isolate and the Ohio SCMV infected the Wsm1 NIL, while the Ohio MDMV and Seehausen SCMV isolates did not. Our results indicate that the three genes, or closely linked loci, provide virus resistance. Resistance conferred by the three genes is influenced by interactions among the genes, the virus species, the virus isolate, and the environment.

Genetic and physical fine mapping of Scmv2, a potyvirus resistance gene in maize

Sugarcane mosaic virus (SCMV) is an important virus pathogen both in European and Chinese maize production, causing serious losses in grain and forage yield in susceptible cultivars. Two major resistance loci confer resistance to SCMV, one located on chromosome 3 (Scmv2) and one on chromosome 6 (Scmv1). We developed a large isogenic mapping population segregating in the Scmv2, but not the Scmv1 region, to minimize genetic variation potentially affecting expression of SCMV resistance. We fine mapped Scmv2 to a region of 0.28 cM, covering a physical distance of 1.3426 Mb, and developed six new polymorphic SSR markers based on publicly available BAC sequences within this region. At present, we still have three recombinants left between Scmv2 and the nearest polymorphic marker on either side of the Scmv2 locus. The region showed synteny to a 1.6 Mb long sequence on chromosome 12 in rice. Analysis of the public B73 BAC library as well as the syntenic rice region did not reveal any similarity to known resistance genes. However, four new candidate genes with a possible involvement in movement of virus were detected.

Validation of candidate genes putatively associated with resistance to SCMV and MDMV in maize (Zea mays L.) by expression profiling

BackgroundThe potyviruses sugarcane mosaic virus (SCMV) and maize dwarf mosaic virus (MDMV) are major pathogens of maize worldwide. Two loci, Scmv1 and Scmv2, have ealier been shown to confer complete resistance to SCMV. Custom-made microarrays containing previously identified SCMV resistance candidate genes and resistance gene analogs were utilised to investigate and validate gene expression and expression patterns of isogenic lines under pathogen infection in order to obtain information about the molecular mechanisms involved in maize-potyvirus interactions.ResultsBy employing time course microarray experiments we identified 68 significantly differentially expressed sequences within the different time points. The majority of differentially expressed genes differed between the near-isogenic line carrying Scmv1 resistance locus at chromosome 6 and the other isogenic lines. Most differentially expressed genes in the SCMV experiment (75%) were identified one hour after virus inoculation, and about one quarter at multiple time points. Furthermore, most of the identified mapped genes were localised outside the Scmv QTL regions. Annotation revealed differential expression of promising pathogenesis-related candidate genes, validated by qRT-PCR, coding for metallothionein-like protein, S-adenosylmethionine synthetase, germin-like protein or 26S ribosomal RNA.ConclusionOur study identified putative candidate genes and gene expression patterns related to resistance to SCMV. Moreover, our findings support the effectiveness and reliability of the combination of different expression profiling approaches for the identification and validation of candidate genes. Genes identified in this study represent possible future targets for manipulation of SCMV resistance in maize.