3 years ago

Deciphering the Theobroma cacao self-incompatibility system: from genomics to diagnostic markers for self-compatibility.

Jean-Luc Verdeil, Michel Boccara, Zoe Wilson, Herman Ebai Ebaiarrey, Thierry Legavre, Christine Sanier, Rey Gaston Loor Solorzano, Uilson Lopes, Didier Clément, Karina Peres Gramacho, Ives Bruno Efombagn Mousseni, Gabor Gyapay, Kelly Colonges, Marcos Ramos Da Silva, Marie Claire Eyango, Géraldine Mastin, Ronan Rivallan, Benoit Mermaz, Olivier Sounigo, Olivier Fouet, Nicholas Cryer, Xavier Argout, Claire Lanaud
Cocoa self-compatibility is an important yield factor and has been described as being controlled by a late gameto-sporophytic system expressed only at the level of the embryo sac. It results in gametic non-fusion and involves several loci. In this work, we identified two loci, located on chromosomes 1 and 4 (CH1 and CH4), involved in cocoa self-incompatibility by two different processes. Both loci are responsible for gametic selection, but only one (the CH4 locus) is involved in the main fruit drop. The CH1 locus acts prior to the gamete fusion step and independently of the CH4 locus. Using fine-mapping and genome-wide association studies, we focused analyses on restricted regions and identified candidate genes. Some of them showed a differential expression between incompatible and compatible reactions. Immunolocalization experiments provided evidence of CH1 candidate genes expressed in ovule and style tissues. Highly polymorphic simple sequence repeat (SSR) diagnostic markers were designed in the CH4 region that had been identified by fine-mapping. They are characterized by a strong linkage disequilibrium with incompatibility alleles, thus allowing the development of efficient diagnostic markers predicting self-compatibility and fruit setting according to the presence of specific alleles or genotypes. SSR alleles specific to self-compatible Amelonado and Criollo varieties were also identified, thus allowing screening for self-compatible plants in cocoa populations.

Publisher URL: http://doi.org/10.1093/jxb/erx293

DOI: 10.1093/jxb/erx293

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