Abstract
Meiosis is a process of essential importance for sexual reproduction, as it leads to production of gametes. The recombination event (crossing-over) generates genetic variation by introducing new combination of alleles. The first step of crossing-over is introduction of a targeted double-strand break (DSB) in DNA. DMC1 (Disrupted Meiotic cDNA1) is a recombinase that is specific only for cells undergoing meiosis and takes part in repair of such DSBs by searching and invading homologous sequences that are subsequently used as a template for the repair process. Although role of the DMC1 gene has been validated in Arabidopsis thaliana, a functional analysis of its homolog in barley, a crop species of significant importance in agriculture, has never been performed. Here, we describe the identification of barley mutants carrying substitutions in the HvDMC1 gene. We performed mutational screening using TILLING (Targeting Induced Local Lesions IN Genomes) strategy and the barley TILLING population, HorTILLUS, developed after double-treatment of spring barley cultivar ‘Sebastian’ with sodium azide and N-methyl-N-nitrosourea. One of the identified alleles, dmc1.c, was found independently in two different M2 plants. The G2571A mutation identified in this allele leads to a substitution of the highly conserved amino acid (arginine-183 to lysine) in the DMC1 protein sequence. Two mutant lines carrying the same dmc1.c allele show similar disturbances during meiosis. The chromosomal aberrations included anaphase bridges and chromosome fragments in anaphase/telophase I and anaphase/telophase II, as well as micronuclei in tetrads. Moreover, atypical tetrads containing three or five cells were observed. A highly increased frequency of all chromosome aberrations during meiosis have been observed in the dmc1.c mutants compared to parental variety. The results indicated that DMC1 is required for the DSB repair, crossing-over and proper chromosome disjunction during meiosis in barley.
Highlights
Meiosis is a process of essential significance for sexual reproduction
It is suggested that DMC1 promotes only the CO recombination with the homologous chromosome, which is unique to meiosis, and RAD51 plays its role mainly in sister chromatid exchange or the NCO recombination (Shinohara and Shinohara, 2004; Neale and Keeney, 2006)
Our results indicate that DMC1 is involved in the double-strand break (DSB) repair, crossing-over and chromosome disjunction during meiosis process in barley
Summary
Meiosis is a process of essential significance for sexual reproduction. During meiosis distribution of genetic material to gametes is associated with recombination which is achieved through crossing over and chromosome segregation. DMC1 and RAD51 belong to the same protein family of recombinases, involved in DNA repair through HR, which are related to the bacterial RecA (Bianco et al, 1998) They catalyze the process of pairing and invasion of 3 ssDNA tails formed at the DSB sites into homologous doublestranded DNA. Both of these proteins take part in the meiotic recombination events, DMC1 is specific only for cells undergoing meiosis, while RAD51 is ubiquitous and acts in DSB repair in somatic cells. A recent work has shown that in the case of absence of the RAD51mediated strand exchange activity, the DMC1 activity is sufficient to repair all DSBs during meiosis into both CO and NCO products and it does not affect meiotic crossing-over rates or patterns (Cloud et al, 2012; Da Ines et al, 2013; Singh et al, 2017)
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