A Parthenogenesis Gene Candidate and Evidence for Segmental Allopolyploidy in Apomictic Brachiaria decumbens

• DOI: 10.1534/genetics.116.190314
• Publication Date: 2016-05-23T07:50:43Z
• Authors: Margaret Worthington; Christopher Heffe...; Diana Bernal; Constanza Quintero; Yeny Patricia Zapata; Juan Guillermo Perez; Jose De Vega; John Miles; Stephen Dellaporta; Joe Tohme
• Keywords: 0301 basic medicine; hibridación; Genotype; Genetic Linkage; Parthenogenesis; Brachiaria; poliploidy; Investigations; Polymorphism, Single Nucleotide; Chromosomes, Plant; Polyploidy; 03 medical and health sciences; mapas genéticos; genotypes; Reproduction, Asexual; plant breeding; hybridization; Arabidopsis Proteins; poliploidia; marcadores genéticos; Chromosome Mapping; restriction fragment; genotipos; brachiaria decumbens; feed crops; genetic maps; Seeds; genetic markers; apomixis; Apomixis; Transcription Factors

Abstract Apomixis, asexual reproduction through seed, enables breeders to identify and faithfully propagate superior heterozygous genotypes by seed without the disadvantages of vegetative propagation or the expense and complexity of hybrid seed production. The availability of new tools such as genotyping by sequencing and bioinformatics pipelines for species lacking reference genomes now makes the construction of dense maps possible in apomictic species, despite complications including polyploidy, multisomic inheritance, self-incompatibility, and high levels of heterozygosity. In this study, we developed saturated linkage maps for the maternal and paternal genomes of an interspecific Brachiaria ruziziensis (R. Germ. and C. M. Evrard) × B. decumbens Stapf. F1 mapping population in order to identify markers linked to apomixis. High-resolution molecular karyotyping and comparative genomics with Setaria italica (L.) P. Beauv provided conclusive evidence for segmental allopolyploidy in B. decumbens, with strong preferential pairing of homologs across the genome and multisomic segregation relatively more common in chromosome 8. The apospory-specific genomic region (ASGR) was mapped to a region of reduced recombination on B. decumbens chromosome 5. The Pennisetum squamulatum (L.) R.Br. PsASGR-BABY BOOM-like (psASGR–BBML)-specific primer pair p779/p780 was in perfect linkage with the ASGR in the F1 mapping population and diagnostic for reproductive mode in a diversity panel of known sexual and apomict Brachiaria (Trin.) Griseb. and P. maximum Jacq. germplasm accessions and cultivars. These findings indicate that ASGR–BBML gene sequences are highly conserved across the Paniceae and add further support for the postulation of the ASGR–BBML as candidate genes for the apomictic function of parthenogenesis.