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Plant Mol Biol. 2019 Feb 9. doi: 10.1007/s11103-019-00832-y. [Epub ahead of print]

Resistant and susceptible cacao genotypes exhibit defense gene polymorphism and unique early responses to Phytophthora megakarya inoculation.

Author information

1
Centre National de Recherche Agronomique, Laboratoire Central de Biotechnologie, 01 BP 1740, Abidjan 01, Côte d'Ivoire.
2
Department of Plant Sciences, Life Sciences Building, Pennsylvania State University, University Park, PA, 16802, USA.
3
Intercollege Graduate Degree Program in Ecology, Pennsylvania State University, University Park, PA, 16802, USA.
4
The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA.
5
Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA, 16802, USA.
6
Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
7
Department of Plant Sciences, Life Sciences Building, Pennsylvania State University, University Park, PA, 16802, USA. mjg9@psu.edu.
8
The Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA. mjg9@psu.edu.

Abstract

Key genes potentially involved in cacao disease resistance were identified by transcriptomic analysis of important cacao cultivars. Defense gene polymorphisms were identified which could contribute to pathogen recognition capacity. Cacao suffers significant annual losses to the water mold Phytophthora spp. (Oomycetes). In West Africa, P. megakarya poses a major threat to farmer livelihood and the stability of cocoa production. As part of a long-term goal to define key disease resistance genes in cacao, here we use a transcriptomic analysis of the disease-resistant cacao clone SCA6 and the susceptible clone NA32 to characterize basal differences in gene expression, early responses to infection, and polymorphisms in defense genes. Gene expression measurements by RNA-seq along a time course revealed the strongest transcriptomic response 24 h after inoculation in the resistant genotype. We observed strong regulation of several pathogenesis-related genes, pattern recognition receptors, and resistance genes, which could be critical for the ability of SCA6 to combat infection. These classes of genes also showed differences in basal expression between the two genotypes prior to infection, suggesting that prophylactic expression of defense-associated genes could contribute to SCA6's broad-spectrum disease resistance. Finally, we analyzed polymorphism in a set of defense-associated receptors, identifying coding variants between SCA6 and NA32 which could contribute to unique capacities for pathogen recognition. This work is an important step toward characterizing genetic differences underlying a successful defense response in cacao.

KEYWORDS:

Defense response; Phytophthora megakarya; Theobroma cacao; Transcriptome

PMID:
30739243
DOI:
10.1007/s11103-019-00832-y

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