In a development that could help protect one of the world's most beloved agricultural commodities, a research team at Penn State has successfully created disease-resistant cacao plants using gene-editing technology. According to the researchers, the innovation promises to help resolve a significant problem for the global chocolate industry, worth over $135 billion annually, which faces threat from the phytophthora species, a fungal-like pathogen that gives rise to the destructive black pod disease that can cause yield losses of up to 30% worldwide.
In findings recently posted online in Plant Biotechnology Journal in advance of print publication this fall, the researchers reported that they edited the gene TcNPR3 in cacao plants, ultimately resulting in cacao plants that had 42% smaller disease lesions when infected with phytophthora, compared to non-edited plants.
"Cacao farmers, particularly those with limited economic resources, struggle to implement expensive disease-control measures," said team leader Mark Guiltinan, professor of plant molecular biology in the College of Agricultural Sciences and first author on the study. "And many genetic modification approaches are met with stigma because foreign DNA is left in the final product. Our approach could solve both of those problems."
The researchers employed CRISPR-Cas9, a gene editing technology that acts like "molecular scissors" to precisely modify DNA sequences in the genome, or the complete instructions encoding proteins and more, of living cells and organisms. This usually works by cutting unwanted genes out of the genome and splicing in transgenes, which are genes from other organisms or modified in the lab to achieve the desired functionality. However, this breakthrough represents the first demonstration of genome-edited, transgene-free cacao plants, meaning the plant's DNA was altered without leaving any foreign DNA in the final product, addressing regulatory concerns and consumer acceptance.
The team specifically edited the gene TcNPR3, which is involved in the plant's defense system, in plant cells, grew the cells into full plants and confirmed that they were less susceptible to the disease in lab tests using plant leaves, called foliar assays. The team crossed these edited plants with non-transgenic - normal cacao plants - resulting in non-transgenic offspring with the desired genetic changes. The researchers sequenced the genomes of parent and offspring plants and found that some offspring retained the beneficial gene edit but no longer had any foreign DNA - they were "clean" edits. The researchers analyzed the clean edits' gene expression and found increased expression of genes involved in plant defense, with some genes downregulated, suggesting TcNPR3 may both suppress and activate certain genes.
