Abstract
The introgression of apomixis in major seed crops, would guarantee self-seeding of superior heterotic seeds over generations. In the grass species Paspalum simplex, apomixis is controlled by a single locus in which recombination is blocked. In the perspective of isolating the genetic determinants of apomixis, we report data on sequencing, in silico mapping and expression analysis of some of the genes contained in two cloned genomic regions of the apomixis locus of P. simplex. In silico mapping allowed us to identify a conserved synteny group homoeologous to the apomixis locus, located on a telomeric position of chromosomes 12, 8, 3 and 4 of rice, Sorghum bicolor, Setaria italica and Brachypodium distachyum, respectively, and on a more centromeric position of maize chromosome 1. Selected genes of the apomixis locus expressed sense and antisense transcripts in reproductively committed cells of sexual and apomictic ovules. Some of the genes considered here expressed apomixis-specific allelic variants which showed partial non-overlapping expression patterns with alleles shared by sexual and apomictic reproductive phenotypes. Our findings open new routes for the isolation of the genetic determinants of apomixis and, in perspective, for its introgression in crop grasses.
Highlights
The genus Paspalum[9] Panicoideae is characterized by an extraordinary plasticity of the reproductive system[10], including strict outcrossing, a variable extent of allowed self-compatibility, and nearly obligate apomixis, i.e. asexual reproduction by seeds[11]
We argued that markers not linked to the ACR in all species of Paspalum belong to genomic regions that are dispensable for the expression of the trait, whereas all those linked to apomixis in multiple Paspalum spp. delineate a genomic portion in which the essential genetic determinants of the trait are likely located
In P. simplex, comparative sequence analysis of genes contained in apomixis-linked BACs clearly points to a genomic region that is syntenic among the five main reference grass species[3,23] and is located in a telomeric position on chromosome 12, 8, 3 and 4 of rice, Sorghum, Setaria and Brachypodium, respectively, and in centromeric area of maize chromosome 1
Summary
The genus Paspalum[9] Panicoideae is characterized by an extraordinary plasticity of the reproductive system[10], including strict outcrossing, a variable extent of allowed self-compatibility, and nearly obligate apomixis, i.e. asexual reproduction by seeds[11]. Comparative mapping of apomixis within the Paspalum genus revealed a low extent of gene movement and divergence at the ACR even among very closely related species[15,16], a portion of the same region, identified by markers of rice chromosome 12 was linked to apomixis in all apomictic species of Paspalum analysed to date[15]. We argued that markers not linked to the ACR in all species of Paspalum belong to genomic regions that are dispensable for the expression of the trait, whereas all those linked to apomixis in multiple Paspalum spp. delineate a genomic portion in which the essential genetic determinants of the trait are likely located Bearing this in mind, we investigated on whether larger areas of synteny could be identified between the ACR of P. simplex and specific regions of grasses (i.e. Sorghum, maize, Brachypodium and Setaria) that are more closely related to Paspalum compared to rice.
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