“Regulating meiosis to hasten crop improvement”

 

  Meiosis is a highly evolved cell division in sexually reproducing eukaryotes, that generates new allelic combinations through recombination in addition to maintaining constant number of chromosomes across generations. During meiosis, a large number of programmed DNA double-strand breaks (DSBs) are formed throughout the genome. Repair of meiotic DSBs facilitates the pairing of homologs and forms crossovers resulting from reciprocal exchange of genetic information between homologous chromosomes. The manipulation of meiotic recombination at will, provides breeders a tool to create a new desirable combination of alleles across genetic loci that could be incorporated to a germ line resulting in the traits being carried to the whole plant as it develops4. However, such traits can be removed/ modified as meiotic recombination continuously occurs in the following generations. Moreover, meiosis maintains the ploidy of the progeny and species identity by limiting cross-breeding between accessions or related species containing different ploidy.

Meiotic division processes could be engineered to adapt the need of a breeding program. Recent progress in the field of targeted recombination technologies, chromosome engineering, and an increasing knowledge in the control of meiotic chromosome segregation has significantly increased the ability to manipulate meiosis4. For the first time, knocking out a characterized gene RECQ4, which is an inhibitor of crossovers in an interspecific hybrid between tomato and its relative wild species using CRISPR/Cas9-mutagenesis resulted in increased recombination between the two genomes3. Effect of targeted recombination on multiple, elite maize populations was tested and the results indicated that the targeted recombination is a most promising breeding approach in enhancing the genetic gain1. Virus induced gene silencing was used to downregulate the expression of a meiotic gene (MSH5) in A. thaliana which transiently modified meiotic recombination in a wildtype hybrid thereby generating 20 different chromosome substitution lines (CSLs) which were used in hybrid recreation or QTL mapping2.

In recent years, studies from Arabidopsis have identified approximately 80 genes regulating meiosis, with most of them involved in recombination. Such studies have contributed to a better understanding of the mechanisms and controls of meiotic DSB and CO formation in plants2. Yet, much remains to be learned, with current knowledge providing basic frameworks for exploring strategies to manipulate meiotic recombination in crops.

Bibliography 

1. BRANDARIZ, S. P. AND BERNARDO, R., 2019, Predicted genetic gains from targeted recombination in elite biparental maize populations. The plant genome, 12(1): 180062.

2. CALVO‐BALTANÁS, V., WIJNEN, C. L., YANG, C., LUKHOVITSKAYA, N., DE SNOO, C. B., HOHENWARTER, L. AND WIJNKER, E., 2020, Meiotic crossover reduction by virus‐induced gene silencing enables the efficient generation of chromosome substitution lines and reverse breeding in Arabidopsis thaliana. The Plant Journal, 104(5): 1437-1452.

3. DE MAAGD, R. A., LOONEN, A., CHOUAREF, J., PELÉ, A., MEIJER‐DEKENS, F., FRANSZ, P. AND BAI, Y., 2020, CRISPR/Cas inactivation of RECQ 4 increases homeologous crossovers in an interspecific tomato hybrid. Plant Biotechnology Journal, 18(3): 805-813.

4. KUO, P., DA INES, O. AND LAMBING, C., 2021, Rewiring meiosis for crop improvement. Frontiers in Plant Science, 12: 708948.