RESUMO
The biotrophic oomycete Plasmopara halstedii is the causal agent of downy mildew in sunflower. It penetrates the roots of both susceptible and resistant sunflower lines and grows through the hypocotyls towards the upper part of the seedling. RT-PCR analysis has shown that resistance is associated with the activation of a hsr203J-like gene, which is a molecular marker of the hypersensitive reaction in tobacco. Activation of this gene was specifically observed during the incompatible interaction and coincided with cell collapse in the hypocotyls. This HR was also associated with the early and local activation of the NPR1 gene which is a key component in the establishment of the SAR. No such HR or a significant activation of the hsr203J-like gene were observed during the compatible combination. These results suggest that the resistance of sunflower to P. halstedii is associated with an HR which fails to halt the parasite. By contrast, this HR triggers a SAR which takes places in the upper part of the hypocotyls and eventually leads to the arrest of parasite growth. A model describing the resistance of plants to root-infecting oomycetes is proposed.
Assuntos
Helianthus/microbiologia , Helianthus/fisiologia , Hipocótilo/microbiologia , Hipocótilo/fisiologia , Oomicetos/fisiologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas/genética , Helianthus/genética , Helianthus/imunologia , Peróxido de Hidrogênio/metabolismo , Hipocótilo/imunologia , Oomicetos/imunologia , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Ácido Salicílico/farmacologia , PlântulaRESUMO
Downy mildew caused by Plasmopara halstedii is one of the main diseases causing economic losses in cultivated sunflower. Resistance in this host is conferred by major genes denoted Pl. The inbred sunflower line QIR8, which contains the Pl8 locus and is resistant to all known downy mildew races, was used to isolate a full-length resistance gene analogue (RGA) belonging to the CC-NBC-LRR class of plant resistance genes. The genetically incompatible combination involving downy mildew races 300 and sunflower line QIR8 was characterized by a hypersensitive-like reaction. Semi-quantitative RT-PCR analysis showed that the transcript of Ha-NTIR11g RGA was specifically induced during the incompatible reaction. The transcript was induced approximately 3 d post-infection (dpi), and then decreased by 9 dpi. The high level of transcriptional expression of this RGA coincides with a transcript accumulation of the hsr203J gene which is a marker of the hypersensitive reaction. Treatment with signalling molecules, including salicylic acid and methyl jasmonate, did not activate transcription of the Ha-NTIR11g gene, indicating that Ha-NTIR11g expression is not regulated by defence signalling pathways triggered by these molecules. Ha-NTIR11g was not induced by treatment with hydrogen peroxide or wounding. These results suggest that Ha-NTIR11g RGA may play a critical role in protecting sunflower cells against P. halstedii. The transcript accumulation of R gene-mediated signalling components was also examined.
Assuntos
Regulação da Expressão Gênica de Plantas/fisiologia , Genes de Plantas/fisiologia , Helianthus/genética , Oomicetos/fisiologia , Doenças das Plantas , Acetatos , Ciclopentanos , Helianthus/metabolismo , Helianthus/microbiologia , Peróxido de Hidrogênio , Imunidade Inata/genética , Oxilipinas , Doenças das Plantas/microbiologia , Proteínas de Plantas/metabolismo , Ácido SalicílicoRESUMO
Sunflower downy mildew, caused by Plasmopara halstedii, is one of the major diseases of this crop. Development of elite sunflower lines resistant to different races of this oomycete seems to be the most efficient method to limit downy mildew damage. At least two different gene clusters conferring resistance to different races of P. halstedii have been described. In this work we report the cloning and mapping of two full-length resistance gene analogs (RGA) belonging to the CC-NBC-LRR class of plant resistance genes. The two sequences were then used to develop 14 sequence tagged sites (STS) within the Pl5/Pl8 locus conferring resistance to a wide range of P. halstedii races. These STSs will be useful in marker-assisted selection programs.
Assuntos
Mapeamento Cromossômico , Helianthus/genética , Imunidade Inata/genética , Oomicetos , Doenças das Plantas/microbiologia , Sequência de Aminoácidos , Sequência de Bases , Southern Blotting , Primers do DNA , DNA Complementar/genética , Marcadores Genéticos/genética , Dados de Sequência Molecular , Técnicas de Amplificação de Ácido Nucleico , Doenças das Plantas/genética , Reação em Cadeia da Polimerase , Alinhamento de Sequência , Análise de Sequência de DNA , Sitios de Sequências RotuladasRESUMO
The resistance of sunflower, Helianthus annuus L., to downy mildew, caused by Plasmopara halstedii, is conferred by major genes denoted by Pl. Using degenerate and specific primers, 16 different resistance gene analogs (RGAs) have been cloned and sequenced. Sequence comparison and Southern-blot analysis distinguished six classes of RGA. Two of these classes correspond to TIR-NBS-LRR sequences while the remaining four classes correspond to the non-TIR-NBS-LRR type of resistance genes. The genetic mapping of these RGAs on two segregating F2 populations showed that the non-TIR-NBS-LRR RGAs are clustered and linked to the Pl5/ Pl8 locus for resistance to downy mildew in sunflower. These and other results indicate that different Pl loci conferring resistance to the same pathogen races may contain different sequences.
Assuntos
Marcadores Genéticos , Helianthus/genética , Oomicetos/patogenicidade , Proteínas de Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , Clonagem Molecular , Primers do DNA , Ligação Genética , Genótipo , Helianthus/microbiologia , Dados de Sequência Molecular , Família Multigênica , Homologia de Sequência de AminoácidosRESUMO
Resistance of sunflower to the obligate parasite Plasmopara halstedii is conferred by specific dominant genes, denoted Pl. The Pl6 locus confers resistance to all races of P. halstedii except one, and must contain at least 11 tightly linked genes each giving resistance to different downy mildew races. Specific primers were designed and used to amplify 13 markers covering a genetic distance of about 3 cM centred on the Pl6 locus. Cloning and sequence analysis of these 13 markers indicate that Pl6 contains conserved genes belonging to the TIR-NBS-LRR class of plant resistance genes.
RESUMO
The establishment of a plant-pathogen interaction involves changes in gene expressions in both organisms. To isolate Helianthus annuus genes whose expression is induced during processes of resistance to Plasmopara halstedii, a comparison of the expression pattern of healthy sunflowers was made with sunflowers infected with 2 races of P. halstedii, either virulent or avirulent, using differential display of mRNA. A full-length cDNA, HaAC1, representing a sunflower gene whose expression is enhanced during early stages of the incompatible interaction, was isolated. Different timing of RNA accumulation is observed between compatible and incompatible combinations. Sequence analysis and database search revealed significant homology with auxin-induced genes from plants. The expression of this gene, is also induced after treatment with 2,4-dichlorophenoxyacetic acid (2,4-D), salicylic acid (SA) and wounding.
Assuntos
Genes de Plantas/genética , Helianthus/genética , Ácidos Indolacéticos/farmacologia , Ácido 2,4-Diclorofenoxiacético/farmacologia , Sequência de Aminoácidos , Clonagem Molecular , DNA Complementar/química , DNA Complementar/genética , DNA Complementar/isolamento & purificação , DNA de Plantas/análise , DNA de Plantas/genética , Fungos/fisiologia , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Helianthus/efeitos dos fármacos , Helianthus/microbiologia , Herbicidas/farmacologia , Dados de Sequência Molecular , RNA Mensageiro/efeitos dos fármacos , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Análise de Sequência de DNA , Homologia de Sequência de AminoácidosRESUMO
A candidate-gene approach to analyse the resistance of plants to phytopathogenic fungi is presented. The resistance of sunflower (Helianthus annuus L.) to downy mildew (Plasmopara halstedii) shows a gene-for-gene interaction (monogenic resistance), whereas resistance to white rot (Sclerotinia sclerotiorum) is quantitative, with different levels of resistance for different plant parts. By homology cloning, probes were obtained homologous to some plant resistance genes (nucleotide binding site-like, NBS, genes and serine-threonine protein kinase-like, PK, genes). These clones were used as probes for linkage mapping of the corresponding genes. It was demonstrated that at least three NBS-like loci are located on linkage-group 1, in the region where downy mildew resistance loci have been described. Quantitative trait loci for S. sclerotiorum resistance to penetration or extension of the mycelium in different tissues were studied in three crosses. Major QTLs for resistance were found on linkage group 1, with up to 50% of the phenotypic variability explained by peaks at the map position of the PK locus, 25â cM from the downy mildew loci.
RESUMO
The Pl1 locus in sunflower, Helianthus annuus L., conferring resistance to downy mildew, Plasmopara halstedii, race 1 has been located in linkage group 1 of the consensus RFLP map of the cultivated sunflower. Bulked segregant analyses were used on 135 plants of an F2 progeny from a cross between a downy mildew susceptible line, GH, and RHA266, a line carrying Pl1. Two RFLP markers and one RAPD marker linked to the Pl1 locus have been identified. The RFLP markers are located at 5.6 cM and 7.1 cM on either side of Pl1. The RAPD marker is situated at 43.7 cM from Pl1. The significance and applications of these markers in sunflower breeding are discussed.