Abstract
Apomixis, the formation of asexual seeds in plants, leads to populations that are genetically uniform maternal clones. The transfer of apomixis to crop plants holds great promise in plant breeding for fixation of heterozygosity and hybrid vigour because it would allow the propagation of hybrids over successive generations1,2. Apomixis involves the production of unreduced (diploid) female gametes that retain the genotype of the parent plant (apomeiosis), followed by parthenogenetic development of the egg cell into an embryo and the formation of functional endosperm3. The molecular mechanisms underlying apomixis are unknown. Here we show that mutation of the Arabidopsis gene DYAD/SWITCH1 (SWI1)4,5, a regulator of meiotic chromosome organization, leads to apomeiosis. We found that most fertile ovules in dyad plants form seeds that are triploid and that arise from the fertilization of an unreduced female gamete by a haploid male gamete. The unreduced female gametes fully retain parental heterozygosity across the genome, which is characteristic of apomeiosis. Our results show that the alteration of a single gene in a sexual plant can bring about functional apomeiosis, a major component of apomixis.
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Acknowledgements
We thank V. Vijaybhaskar and V. Subbiah for characterization of the ET60 transposon line; S. Andreuzza, J. Dhawan, S. Mayor, B. Nishal, M. Ramaswami, A. Ray and O. Siddiqi for comments on the manuscript; and the ABRC for seeds. This work was supported by the Council for Scientific and Industrial Research (CSIR; Government of India), and a Centre of Excellence grant from the Department of Biotechnology (to I.S.). M.R. and M.M. were supported by fellowships from the University Grants Commission and the CSIR, respectively.
Author Contributions M.P.M. conducted the experiments on marker gene expression and interpreted the results. M.R. and I.S. planned, and M.R. performed, the remaining experiments and interpreted the results. I.S. wrote the paper with input from M.R.
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This file contains: Supplementary Figure 1 detailing mutant alleles and phenotypes for SWI1; Supplementary Figure 2 showing variation in pollen size; and Supplementary Note 1 showing estimation of triploid formation in dyad versus wild type. (PDF 1167 kb)
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Ravi, M., Marimuthu, M. & Siddiqi, I. Gamete formation without meiosis in Arabidopsis. Nature 451, 1121–1124 (2008). https://doi.org/10.1038/nature06557
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DOI: https://doi.org/10.1038/nature06557
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