ZmCom1 Is Required for Both Mitotic and Meiotic Recombination in Maize

Abstract

CtIP/Ctp1/Sae2/Com1, a highly conserved protein from yeast to higher eukaryotes, is required for DNA double-strand break repair through homologous recombination (HR). In this study, we identified and characterized the COM1 homolog in maize. The ZmCom1 gene is abundantly expressed in reproductive tissues at meiosis stages. In ZmCom1-deficient plants, meiotic chromosomes are constantly entangled as a formation of multivalents and accompanied with chromosome fragmentation at anaphase I. In addition, the formation of telomere bouquet, homologous pairing and synapsis were disturbed. The immunostaining assay showed that the localization of ASY1 and DSY2 was normal, while ZYP1 signals were severely disrupted in Zmcom1 meiocytes, indicating that ZmCom1 is critically required for the proper SC assembly. Moreover, RAD51 signals were almost completely absent in Zmcom1 meiocytes, implying that COM1 is required for RAD51 loading. Surprisingly, in contrast to the Atcom1 and Oscom1 mutants, Zmcom1 mutant plants exhibited a number of vegetative phenotypes under normal growth condition, which may be partly attributed to mitotic aberrations including chromosomal fragmentation and anaphase bridges. Taken together, our results suggest that although the roles of COM1 in HR process seem to be primarily conserved, the COM1 dysfunction can result in the marked dissimilarity in mitotic and meiotic outcomes in maize compared to Arabidopsis and rice. We suggest that this character may be related to the discrete genome context.

COM1, a factor of alternative non‐homologous end joining, lagging behind the classic non‐homologous end joining pathway in rice somatic cells

“…Com1/Sae2 was first identified in Saccharomyces cerevisiae (Prinz et al, 1997;McKee and Kleckner, 1997) with an indispensable role in meiosis. In subsequent years, Com1/Sae2 homologs have been identified in mammals (Schaeper et al, 1998), fission yeast (Limbo et al, 2007), Caenorhabditis elegans (Penkner et al, 2007), Arabidopsis (Uanschou et al, 2007), Tetrahymena (Lukaszewicz et al, 2010), Oryza sativa (Ji et al, 2012), and Zea mays (Wang et al, 2018). As the specific mechanisms in S. cerevisiae, Sae2 acts together with the MRX complex to initiate 5'-3' end resection by endonucleolytic cleavage, and the resulting 3' single-strand is subsequently used for Rad51 or Dmc1-catalyzed strand invasion to initiate homology-directed repair (Cannavo and Cejka, 2014;Garcia et al, 2011;Neale et al, 2005).…”

ZmRAD17 Is Required for Accurate Double-Strand Break Repair During Maize Male Meiosis

“…Chromosome fragmentation and entanglement are characteristic phenomena observed in mutants deficient in DSB repair machinery. Like the Osrad17 mutants (Hu et al, 2018) and other related mutants such as Zmcom1 (Wang et al, 2018), Zmrad51c (Jing et al, 2019), Osxrcc3 (Zhang et al, 2015), Atrad50 (Gallego et al, 2001;Bleuyard et al, 2004) and Atmre11 (Samanic et al, 2013(Samanic et al, , 2016, the Zmrad17 mutants showed the presence of chromosome fragmentation at prophase I. However, the severity of chromosome aberration seemed to be much less in Zmrad17 when compared to the Osrad17 mutants.…”

“…HR is initiated by the programmed formation of DNA double-strand breaks (DSBs), which are catalyzed by a topoisomerase-like protein SPO11 and several accessory proteins (Keeney et al, 1997;Lam and Keeney, 2015). DSB sites are further resected by a protein complex known as MRX/N (Mre11-Rad50-Xrs2/Nbs1) and Sae2/Com1/CtIP/Ctp1 (Lamarche et al, 2010;Wang et al, 2018), generating replication protein A (RPA)-coated single-stranded DNA (ssDNA) overhangs (Mimitou and Symington, 2009). Then, RPA is replaced by the RecA recombinases RAD51 and DMC1 forming nucleoprotein filaments and promoting homology search and single strand invasion to produce recombination intermediates called as the displacement (D)-loop Cloud et al, 2012).…”

ZmMTOPVIBis essential for double-strand break formation and bipolar spindle assembly during maize meiosis

“…To investigate whether defective ZmMTOPVIB disrupts homologous chromosome pairing, we performed fluorescence in situ hybridization (FISH) using the 5S rDNA probe in wild type and the ZmmtopVIB-1 mutant. The 5S rDNA is a tandem repeat sequence located on the long arm of chromosome 2 that is routinely used to evaluate chromosome pairing and segregation in maize (Wang et al, 2018). In wild type meiocytes, two 5S signals gradually pair with each other during zygotene ( Figure The telomere bouquet is an evolutionarily conserved chromosome arrangement that clusters telomeres in a small region on the nuclear envelope (Tomita and Cooper, 2007;Moiseeva et al, 2017).…”