At FG genesis, RBR, LACHESIS, BLH1, MYB64 and MYB119 are involved in the regulation of mitosis of FM and the cellularization of FG (Gross-Hardt et al., 2007 Ingouff et al., 2009 Pagnussat et al., 2007 Rabiger and Drews, 2013). The main studies focusing on Arabidopsis, for example, show that SPL, WUS, MAC1 are involved in regulating the transformation of somatic cells to germ cells, MSP1 in regulation of the number of MMC, and SWI1, ARP6 in regulation of meiosis of MMC (Boateng et al., 2008 Lieber et al., 2011 Nonomura et al., 2003 Qin et al., 2014 Sheridan et al., 1996 Yang et al., 1999). Then, though three consecutive nuclear mitosis, the FM further develops into the seven-celled embryo sac (Drews and Koltunow, 2011 Nakajima, 2018).
From megaspore mother cell (MMC) to functional megaspore (FM) is the meiotic stage.
In most angiosperms, the development of female gametophytes (FGs) generally includes megasporogenesis and FG genesis. Therefore, it will be important to explore the genes related to plant female fertility and meiosis. In the past two decades, on account of a persistent barrier to mutant acquisition and character identification, the research addressing female sterility has been slower in rice. Meiosis is a key process in rice reproductive development. The fertility of the female reproductive system determines the grain yield and the success of heterosis. The fsv1 and OsMLH3-knockout lines are valuable germplasms for development of female sterile restorer lines for mechanized seed production of hybrid rice. OsMLH3 and OsMLH1 (MutL-homolog 1) interact to form a heterodimer (MutLγ) to promote crossover formation in the macrospore and microspore mother cells and development of functional megaspore during meiosis, defective OsMLH3 or OsMLH1 in fsv1 and CRISPR/Cas9-based knockout lines results in reduced type I crossover and bivalent frequency. Through map-based cloning and functional analyses, we isolated the causal gene of fsv1, OsMLH3 encoding a MutL-homolog 3 protein, an ortholog of HvMLH3 in barley and AtMLH3 in Arabidopsis. Here, we report the characterization of a spontaneous rice female sterile variation 1 mutant ( fsv1) that showed severe embryo sacs abortion with low seed-setting rate. The development of embryo sacs is crucial for seed production in plants, but the genetic basis regulating the meiotic crossover formation in the macrospore and microspore mother cells remains largely unclear.
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