Abstract
In previous studies we reported the identification of several AFLP, RAPD and RFLP molecular markers linked to apospory in Paspalum notatum. The objective of this work was to sequence these markers, obtain their flanking regions by chromosome walking and perform an in silico mapping analysis in rice and maize. The methylation status of two apospory-related sequences was also assessed using methylation-sensitive RFLP experiments. Fourteen molecular markers were analyzed and several protein-coding sequences were identified. Copy number estimates and RFLP linkage analysis showed that the sequence PnMAI3 displayed 2–4 copies per genome and linkage to apospory. Extension of this marker by chromosome walking revealed an additional protein-coding sequence mapping in silico in the apospory-syntenic regions of rice and maize. Approximately 5 kb corresponding to different markers were characterized through the global sequencing procedure. A more refined analysis based on sequence information indicated synteny with segments of chromosomes 2 and 12 of rice and chromosomes 3 and 5 of maize. Two loci associated with apomixis locus were tested in methylation-sensitive RFLP experiments using genomic DNA extracted from leaves. Although both target sequences were methylated no methylation polymorphisms associated with the mode of reproduction were detected.
Highlights
Apomixis is a route of asexual reproduction through seeds (Nogler, 1984)
Two RAPD and 14 AFLP molecular markers previously reported to be completely linked to apospory in tetraploid P. notatum were re-amplified using the corresponding primers from genotypes Q4188, Q4117 and their F1 hybrids (55 sexual and 10 aposporous)
The availability of experimentally-generated tetraploid sexual genotypes of P. notatum that can be used as female parents in crosses with natural apomictic tetraploid plants has allowed the generation of populations that segregate according to the mode of reproduction without the need to use inter-specific or inter-ploid crosses
Summary
Apomixis is a route of asexual reproduction through seeds (Nogler, 1984). This mode of reproduction has been described in about 400 genera from 40 plant families and seems to have arisen multiple times during evolution (Carman, 1997). Apomixis avoids meiosis and fertilization of the egg cell to generate progeny that are clones of the mother plant (Savidan, 2000). The type of apomixis found in the Poaceae, embryo sacs bearing non-reduced nuclei are formed from the megaspore mother cell itself (diplospory) or from nucellar cells (apospory), followed by development of the embryo through parthenogenesis from unreduced (2n) egg cells.
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