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Fine mapping of angular leaf spot resistance loci in common bean (Phaseolus vulgaris L.)

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Paula Rodrigues Oblessuc
Total Authors: 1
Document type: Doctoral Thesis
Press: Campinas, SP.
Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
Defense date:
Examining board members:
Luciana Lasry Benchimol Reis; Maria Lucia Carneiro Vieira; Maria Imaculada Zucchi; Monalisa Sampaio Carneiro; Rosana Pereira Vianello
Advisor: Luciana Lasry Benchimol Reis; Luis Eduardo Aranha Camargo

The common bean (Phaseolus vulgaris L.) is an important protein source in human diet. The angular leaf spot (ALS), caused by the fungus Pseudocercospora griseola (Sacc.) Crous & Braun, leads to great common bean yield losses. The common bean breeding search for tools that improve the transferring of disease resistance genes to developing cultivars. Therefore, the objective of the present work was study the genetic and molecular mechanisms enrolled in the common bean responses to ALS, and with this contribute to this crop breeding. Initially, ALS resistance QTLs were identified using the UC (IAC-UNA x CAL 143) mapping population based on the genetic map previously developed with microsatellites markers. The quantitative study of the ALS disease severity reveals normal and transgressive distribution on the UC population, with quantitative resistance observed in CAL 143. Seven QTLs were mapped in five different common bean linkage groups. Of these, the ALS10.1 locus showed major effect (16% - 22%) and stability in all three environments analyzed: (1) natural infection conditions in the dry season; (2) natural infection conditions in wet season; and (3) race-specific controlled infection conditions in greenhouse. The ALS10.1 locos region was saturated with microsatellites, SCARs and Sequence-Tagged Site-DArTs (STS-DArTs) markers; the latter using the bulk segregant analysis (BSA). The confidence interval was reduced from 13.4 cM to 3.0 cM after the locus saturation, which had the markers number increased from four to 10. The study of the ALS10.1 genomic context through the alignment of the markers to the draft of the common bean genome enabled the identification of the QTL core at the end of the chromosome Pv10, with approximately 3.5 Mb. The Gene Ontology (GO) analyses of the 323 predicted genes for this genomic region demonstrated that 61.6% of the genes are involved in stress responses. A TIR-NB-ARC gene cluster (domains highly conserved in Resistance (R) genes), was observed covering approximately 849 Kb on the ALS10.1 core region; besides this region also presents other genes known to be related to plant immunity. Seven genes on ALS10.1 core region were selected based on the role in pathogen resistance of the respective Arabidopsis thaliana orthologs, and had their gene expression pattern evaluated in response to P. griseola. The R gene TIR-NB-ARC was induced during the compatible response of the genotype IAC-UNA; therewith it should enable the pathogen proliferation, probably through the fungus Avr recognition, blocking the defense response. In addition, putative negative regulator genes of immune response through the inactivation of salicylic acid (SA) via were repressed during the incompatible response of the CAL 143. The SA is a key hormone to pathogen induced plant defense response. Therefore, the common bean pathogen recognition should take place through the R genes to the downstream signaling of the SA-mediated defense response. The results of the present work will enable the manipulation of the bean genetic diversity by the breeder either by introgression and pyramiding of resistance genes through marker assisted selection or transgenesis; or by the identification of genetically resistant cultivars through gene expression analysis (AU)

FAPESP's process: 09/02411-2 - Fine mapping of angular leaf spot resistance in common bean (Phaseolus vulgaris L.)
Grantee:Paula Rodrigues Oblessuc
Support type: Scholarships in Brazil - Doctorate