Journal of Energy Bioscience 2024, Vol.15, No.3, 135-146 http://bioscipublisher.com/index.php/jeb 139 4.3 Key research papers Key research papers have laid the foundation for cassava as a bioenergy research subject. The progress in cassava molecular breeding, particularly for bioenergy development, has been substantial. Studies have focused on enhancing stress resistance and starch content through genetic engineering, which is crucial for bioenergy crops (Pen, 2014). Additionally, the potential of cassava as a bioenergy crop has been further explored through insights into photosynthesis and associated physiology, aiming to improve yield potential (Souza et al., 2017). These studies, along with others that have engineered disease resistance (Figure 1) (Bart and Taylor, 2017) and addressed the challenges of clonal propagation (Wolfe et al., 2015), have been instrumental in advancing cassava as a viable bioenergy source. Figure 1 Genome-editing strategies to create resistance against three major pathogens of cassava (Adopted from Bart and Taylor, 2017) Note: Left: Cassava brown streak disease (CBSD) is caused by two potyviruses; In other species, mutation of eukaryotic translation initiation factor 4E (eIF4E) family of genes promotes disease resistance; It is predicted that a similar strategy may be effective in cassava; Middle: Cassava mosaic disease (CMD) is widely controlled by the yet to be identified CMD2 resistance mechanism; For unknown reasons, passage of cassava cells through somatic embryogenesis disrupts CMD2-mediated resistance; A potential explanation involves loss of methylation (Me) that releases expression of a negative regulator of CMD2; In this case, it should be possible to use guide RNAs complexed with Cas9 to introduce genetic changes that stably disrupt expression of the negative regulator; Right: Cassava bacterial blight disease is caused by Xanthomonas axonopodis pv. Manihotis (Xam). Xam injects transcription activator like (TAL) effectors into plant cells, which activate expression of MeSWEET10a by directly binding to its promoter; The binding site overlaps with the TATA box; Using homolog recombination, it would be possible to mutate the binding site, maintain the TATA box, and disrupt TAL effector binding by Bart and Taylor (2017) The outlined genome-editing strategies by Bart and Taylor, 2017 represent a significant breakthrough in cassava research, providing a focused approach to combating its most devastating diseases. By targeting the eukaryotic translation initiation factor (eIF4E) for CBSD, manipulating methylation patterns or gene expression for CMD, and altering binding sites for TAL effectors in CBB, these strategies employ precision breeding to enhance disease resistance. This methodological advancement not only improves cassava's resilience to pathogens but also exemplifies the potential of CRISPR/Cas9 and other genome-editing tools in crop improvement. The integration of such technologies into breeding programs promises rapid deployment of disease-resistant cassava varieties, potentially transforming agricultural practices and enhancing food security in regions heavily dependent on cassava.
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