“Meiosis and its regulation”

   Meiosis is a highly evolved cell division in sexually reproducing eukaryotes, that generates new allelic combinations through recombination in addition to maintaining a 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 the reciprocal exchange of genetic information between homologous chromosomes. Sister kinetochores bind to microtubules originating from the same spindle pole during meiosis I, this phenomenon is referred to as mono-orientation and is essential for setting up the reductional mode of chromosome segregation during meiosis I. Mono-orientation depends on a four-component protein complex referred to as monopolin which consists of two nucleolar proteins Csm1 and Lrs4, meiosis-specific protein Mam1 of unknown function, and casein kinase Hrr25. Monopolin complex binds to kinetochores during meiosis I and prevents bipolar attachments in budding yeast.⁴

        Ubiquitination seems to play an enhanced role in meiotic processes in all plants and higher eukaryotes. Significant and varied roles for the ubiquitination cascade in plant meiosis are indicated by transcriptome dynamics and characterization of a small number of ligases ³. Breeders can design a new, desirable combination of alleles across genetic loci using meiotic recombination manipulation, which they can then incorporate into a germ line to carry the traits to the entire plant as it grows ². However, such traits will be 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 meiosis². Recently, 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 technique resulted in increased recombination between the two genomes¹.  Yet, much remains to be learned, with current knowledge providing basic frameworks for exploring strategies to manipulate meiotic recombination in crops.  

Bibliography

1. DE MAAGD, R. A., LOONEN. A., JIHED, C., PELE, A., FIEN, M., PAUL, F. AND BAI, Y., 2020, CRISPR /Cas inactivation of RECQ 4 increases homeologous crossovers in an interspecific tomato hybrid. Plant Biotechnol. J., 18(3): 805-813.

2. KUO, P., DA INES, O. AND LAMBING, C., 2021, Rewiring Meiosis for Crop Improvement. Front. Plant Sci., 12: 708948.

3. ORR, J. N., WAUGH, R. AND COLAS, I., 2021, Ubiquitination in Plant Meiosis: Recent Advances and High Throughput Methods. Front. Plant Sci., 12: 667314.

4. SARKAR, S., RAJESH, T. S., JACOB, Z. D., LOUISE, N., EVA, H., MILLAR, J. B. A. AND PRAKASH, A., 2021, Monopolin Subunit Csm1 Associates with MIND Complex to Establish Monopolar Attachment of Sister Kinetochores at Meiosis I. PLoS Genet., 9(7): 1003610.