Methods for enhancing somatic embryogenesis in Theobroma cacao

Open Access
Erwin, Rachel Lynn
Area of Honors:
Chemical Engineering
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Dr. Wayne Roger Curtis, Thesis Supervisor
  • Dr. Themis Matsoukas, Honors Advisor
  • Theobroma cacao
  • somatic embryogenesis
  • plant propagation
  • PLA
Theobroma cacao, the chocolate tree, is an important cash crop for many countries in Africa and South America, but many trees have become infected with various pathogenic fungi. In order to combat the crop losses due to the fungi, alternative methods of propagation have been explored in order to clonally propagate superior ecotypes of cacao, including somatic embryogenesis (SE). SE is faster and more consistent than previously used methods. Attempts have been made to enhance somatic embryogenesis in plants that are phylogenetically close to cacao, including cotton (Gossypium hirsutum) and rapeseed (Brassica napus). These attempts include embryogenic protein domain (PLA1) addition to the media of cotton and the overexpression of the BABYBOOM (BBM) gene in transgenic rapeseed tissue. Cacao SE is very time-consuming, so an alternative method of study was needed. In order to preliminarily test the effectiveness of these methods for enhancing SE, they were tested on A. thaliana. I had three large efforts in the lab. The first was helping Sergio Florez, a PhD candidate, acquire gene expression level data in cacao at different timepoints during SE. The second was my own experiment to test the effectiveness of embryogenic genes (BBM, AIL5, and LEC2) at enhancing SE in Arabidopsis. The third was another independent experiment to test the effectiveness of PLA1 addition to the media at enhancing SE in Arabidopsis. The results of my experiments show that the overexpression of transcription factors and PLA1 addition did not have a significant effect in enhancing somatic embryogenesis in Arabidopsis. The number of embryos per explant and the percent responsiveness of the tissue did not significantly increase with the addition of PLA1 proteins nor overexpression of genes. However, the SE gene expression analysis in cacao did yield potential genes to be considered for use as biomarkers that would indicate a tissue’s embryogenic potential. More work remains for enhancing somatic embryogenesis, but these preliminary experiments give some insight into methods of increasing crop production via SE.