Applications of New Breeding Technologies for Potato Improvement

Abstract

The first decade of genetic engineering primarily focused on quantitative crop improvement. With the advances in technology, the focus of agricultural biotechnology has shifted toward both quantitative and qualitative crop improvement, to deal with the challenges of food security and nutrition. Potato (Solanum tuberosum L.) is a solanaceous food crop having potential to feed the populating world. It can provide more carbohydrates, proteins, minerals, and vitamins per unit area of land as compared to other potential food crops, and is the major staple food in many developing countries. These aspects have driven the scientific attention to engineer potato for nutrition improvement, keeping the yield unaffected. Several studies have shown the improved nutritional value of potato tubers, for example by enhancing Amaranth Albumin-1 seed protein content, vitamin C content, β-carotene level, triacylglycerol, tuber methionine content, and amylose content, etc. Removal of anti-nutritional compounds like steroidal glycoalkaloids, acrylamide and food toxins is another research priority for scientists and breeders to improve potato tuber quality. Trait improvement using genetic engineering mostly involved the generation of transgenic products. The commercialization of these engineered products has been a challenge due to consumer preference and regulatory/ethical restrictions. In this context, new breeding technolgies like TALEN (transcription activator-like effector nucleases) and CRISPR/Cas9 (clustered regularly interspaced palindromic repeats/CRISPR-associated 9) have been employed to generate transgene-free products in a more precise, prompt and effective way. Moreover, the availability of potato genome sequence and efficient potato transformation systems have remarkably facilitated potato genetic engineering. Here we summarize the potato trait improvement and potential application of new breeding technologies (NBTs) to genetically improve the overall agronomic profile of potato.

Keywords: CRISPR; TALEN; genome editing; nutritional quality; potato.

Figure 1

A schematic diagram of new breeding technologies (NBTs) application for editing potato genome for nutritional improvement. (A) Clustered regularly interspaced short palindromic repeat/CRISPR associated9 (CRISPR/Cas9) system. Expression of constructs containing a single guide RNA (sgRNA) and Cas9 endonuclease will result in the assembly of sgRNAs and Cas9 nuclease to make a sgRNA/Cas9 complex. The designed sgRNA having sequence complementarity will bind specifically to a targeted site on genomic DNA and sgRNA/Cas9 complex will cleave 3' upstream of PAM (protospacer adjacent motif) sequence; shown by black scissors. This cleavage will result in double-stranded brakes (DSB) in targeted genome. (B) Transcription activator-like effector nucleases (TALENs) system. The TALE array contains a highly conserved (33–34 nt) DNA binding domain having repeat variable di-residues (RVDs) at positions 12 and 13 to guide the target-specific binding. Nuclease activity is performed by domains containing FokI endonucleases to produce DSBs. These DSBs are normally repaired by host-mediated DNA repair mechanisms which might results in targeted mutation and end in either gene disruption, correction or addition. The black circles having white text (1,2) represent the CRISPR/Cas9/TALENs cleavage of two host genes (vacuolar invertase, VInv; sterol side chain reductase, SSR2). (C) VInv is primarily involved in bioconversions of sucrose to fructose and glucose inside cell vacuole, precursors of acrylamide formation. (D) Biosynthesis of steroidal glycoalkaloids in plant cell from cycloartenol which is mediated by the activity of host SSR2 gene. NBTs-mediated targeting of host genes will result in reduced formation of anti-nutrients (acrylamide and steroidal glycoalkaloids) inside tubers and thus result in the improved quality of potato tubers. The proposed challenges (rectangles) by using these technologies might result in some questions such as society and regulation regimes' approval for editing food crop, off-site targeting effects on plants, the presence of any transgene, biosafety trails to check health-related issues, and the potential risks of horizontal gene transfer by using these GM crops. These questions need to be addressed while before using some NBTs.