Abstract
BackgroundTheobroma cacao L., the source of cocoa, is a crop of significant economic value around the world. To facilitate the study of gene function in cacao we have developed a rapid Agrobacterium-mediated transient genetic transformation protocol. Here we present a detailed methodology for our transformation assay, as well as an assay for inoculation of cacao leaves with pathogens.ResultsAgrobacteriumtumefaciens cultures are induced then vacuum-infiltrated into cacao leaves. Transformation success can be gauged 48 h after infiltration by observation of green fluorescent protein and by qRT-PCR. We clarify the characteristics of cacao leaf stages and demonstrate that our strategy efficiently transforms leaves of developmental stage C. The transformation protocol has high efficacy in stage C leaves of four of eight tested genotypes. We also present the functional analysis of cacao chitinase overexpression using the transient transformation system, which resulted in decreased pathogen biomass and lesion size after infection with Phytophthora tropicalis.ConclusionsLeaves expressing transgenes of interest can be used in subsequent functional genetic assays such as pathogen bioassay, metabolic analysis, gene expression analysis etc. This transformation protocol can be carried out in 1 day, and the transgenes expressing leaf tissue can be maintained in petri dishes for 5–7 days, allowing sufficient time for performance of additional downstream gene functional analysis. Application of these methods greatly increases the rapidity with which candidate genes with roles in defense can be tested.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-016-0119-5) contains supplementary material, which is available to authorized users.
Highlights
Theobroma cacao L., the source of cocoa, is a crop of significant economic value around the world
Both transformation strategies have been applied to a number of tree crops including cacao [13,14,15,16,17,18,19,20], and it has been applied to enhancement the of disease resistance, abiotic stress response, improvement of quality traits, and general study of functional genetics [21]
The transient transformation procedure described here offers a rapid means of performing functional genetic characterization studies on cacao, a long generation tree crop of significant economic importance
Summary
Agrobacterium tumefaciens cultures are induced vacuum-infiltrated into cacao leaves. Transformation success can be gauged 48 h after infiltration by observation of green fluorescent protein and by qRT-PCR. We clarify the characteristics of cacao leaf stages and demonstrate that our strategy efficiently transforms leaves of developmental stage C. The transformation protocol has high efficacy in stage C leaves of four of eight tested genotypes. We present the functional analysis of cacao chitinase overexpression using the transient transformation system, which resulted in decreased pathogen biomass and lesion size after infection with Phytophthora tropicalis
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