Differential expression of lorelei-like genes in aposporous and sexual Paspalum notatum plants

Abstract

Gametophytic apomictic plants form non-reduced embryo sacs that generate clonal embryos by parthenogenesis, in the absence of both meiosis and egg-cell fertilization. Here we report the sequence and expression analysis of a lorelei-like Paspalum notatum gene, n20gap-1, which encode a GPI-anchored protein associated with apomixis in this species. Phylogeny trees showed that n20gap-1 was evolutionary related to the Arabidopsis thaliana lorelei genes At4g26466 and At5g56170. RFLP (Restriction Fragment Length Polymorphism) analysis revealed the occurrence of several homologous sequences in the Paspalum notatum genome, exhibiting polymorphisms genetically linked to apomixis. Real-time PCR showed that the additive expression of lorelei-family genes presents a minor activity peak at pre-meiosis and a major one at anthesis. Apomictic plants showed a significantly increased activity at pre-meiosis, post-meiosis and anthesis with respect to sexual plants. No significant differential activity was detected at late remeiosis/meiosis. In situ hybridization assays confirmed a non-significant differential expression at late premeiosis, although a moderately increased signal was observed in ovules and pollen mother cells of the sexual genotype. Several ngap-1 alleles differing mainly at the 3´UTR sequence were identified. Two of them (30 and 34) were predominantly expressed. While the lorelei At4g26466 disruption was shown to be detrimental to sperm cell release in arabidopsis, null-mutants of lorelei-like gene At5g56170 did not evidence a distinctive reproductive phenotype. Our results suggest that analysis of gain-of-function lorelei mutants might uncover the occurrence of reproductive developmental alterations related with apomixis.