Gene editing tools may help the main game in crop breeding

New targeted chromosomal editing tools have potential to accelerate crop breeding gains in major crops:

Key Quote:

It seems plausible, at least in concept, that the technology found useful in yeast by Sadhu et al. (2016) can be adapted to eventually obtain F1–derived doubled haploids that have recombination events precisely where a plant breeder wants them. A doubled haploid with targeted recombination may be obtained if the following protocols are developed: (i) a multiplex CRISPR system induces mitotic double-strand breaks at multiple target DNA sequences, (ii) cells with the desired loss-of-heterozygosity events are screened, and (iii) the desired cells are regenerated into whole plants that carry the targeted recombinations.
From the regenerated plants, doubled haploids can be developed via standard procedures that have already been found routinely useful in breeding programs. Doubled haploids that exhibit the targeted recombinations can be identified via markers. In addition to the possible use of CRISPR technology (Sadhu et al., 2016), targeted meiotic recombination via the Spo11 endonuclease is being investigated [Bastianelli and Nicolas, 2015; http://www.meiogenix.com , (accessed 7 Apr. 2017)].

Summary

Advances in clustered regularly interspaced short palindromic repeats (CRISPR) technology have allowed targeted recombination in specific DNA sequences in yeast (Saccharomyces cerevisiae). My objective was to determine if the selection gains from targeted recombination are large enough to warrant the development of targeted recombination technology in plants. Genomewide marker effects for quantitative traits in two maize (Zea mays L.) experiments were used to identify targeted recombination points that would maximize the per-chromosome genetic gains in a given cross. With nontargeted recombination in the intermated B73 × Mo17 population, selecting the best out of 180 recombinant inbreds led to a 7.1% gain for testcross yield. Having one targeted recombination on each of the 10 maize chromosomes led to a predicted gain of 15.3% for yield. Targeted recombination therefore led to a predicted relative efficiency (RETargeted) of (0.153 ÷ 0.071) = 212% of targeted recombination compared with nontargeted recombination. For the five other traits in the intermated B73 × Mo17 population and for four traits in 45 other maize crosses, the RETargeted values ranged from 105 to 600%. The targeted recombination points differed among traits and crosses. Predicted gains increased when the number of targeted recombinations per chromosome increased from one to two. Overall, the results suggested that targeted recombination could double the selection gains for quantitative traits in maize and that the development of targeted recombination technology is worthwhile. Empirical experiments with current marker-assisted breeding procedures are needed to validate the per-chromosome predicted gains.

• Bernardo, R. 2017. Prospective Targeted Recombination and Genetic Gains for Quantitative Traits in Maize. Plant Genome 10. doi:10.3835/plantgenome2016.11.0118

See also an earlier post about a wheat breeding article that endorses the same concept