Gene expression analysis at the onset of aposporous apomixis in Paspalum notatum

Abstract

Apomixis is a route of asexual reproduction through seeds, that progresses in the absence of meiosis and fertilization to generate maternal clonal progenies. Gametophytic apomicts are usually polyploid and probably arose from sexual ancestors through a limited number of mutations in the female reproductive pathway. A differential display analysis was carried out on immature inflorescences of sexual and apomictic tetraploid genotypes of Paspalum notatum, in order to identify genes associated with the emergence of apospory. Analysis of approximately 10,000 transcripts led to the identification of 94 high-quality differentially expressed sequences. Assembling analysis, plus validation, rendered 65 candidate unigenes, organized as 14 contigs and 51 singletons. Thirty-four unigenes were isolated from apomictic plants and 31 from sexual ones. A total of 45 (69.2%) unigenes were functionally categorized. While several of the differentially expressed sequences appeared to be components of an extracellular receptor kinase (ERK) signal transduction cascade, others seemed to participate in a variety of central cellular processes like cell-cycle control, protein turnover, intercellular signalling, transposon activity, transcriptional regulation and endoplasmic reticulum-mediated biosynthesis. In silico mapping revealed that a particular group of five genes silenced in apomictic plants clustered in a rice genomic area syntenic with the region governing apospory in Paspalum notatum and Brachiaria brizantha. Two of these genes mapped within the set of apo-homologues in P. notatum. Four genes previously reported to be controlled by ploidy were identified among those expressed differentially between apomictic and sexual plants. In situ hybridization experiments were performed for selected clones.

Identification of Candidate Genes Related to Polyploidy and/or Apomixis in <i>Eragrostis curvula</i>

“…The proportion of polymorphic bands associated with the reproductive mode in inflorescences was relatively low (0.71%). These results agree with previous reports on the aposporous apomictic grass P. notatum [44], where a similar percentage (1.2%) of differentially expressed genes associated with apospory in premeiotic inflorescences was detected using DD. Therefore, the number of genes displaying altered expression in flowers during apomictic development shows a similar order of magnitude for aposporous and diplosporous apomixis.…”

“…Sequences with similar annotations have been reported to be associated with apomixis and/or polyploidy for various other species, including Poa pratensis [53], Paspalum notatum [44,45], potato [54], Pennisetum squamulatum and Cenchrus ciliare [25], Panicum maximum [55], and Paspalum simplex [24,56]. Taking into account our previous results in E. curvula [32,33,35], the results of the present study, and those reported for other species by other authors, there are many commonalities among the different species with respect to apomixis.…”

“…Despite the variations in developmental patterns among the different species, apomixis appears to display conserved features at the molecular level. For example, annotation comparisons among sequences differentially expressed in P. pratensis [53] and P. notatum [44] revealed 5 genes with identical predicted function: outer membrane LRR receptor kinase, kinesin motor protein, GPI anchored protein, UDP glucose glucosyl transferase and ribosomal protein S12 [44]. Several of the candidates differentially expressed in both species seem to be involved in a signal transduction cascade of the ERK type, with deviations controlled by a Ras ortholog and phospholipase C [44].…”

The Genetic Control of Apomixis: Asexual Seed Formation

“…This approach is complicated by the nature of asexual reproduction that prevents the generation of isogenic lines that differ solely with regard to reproductive mode. Nevertheless, transcriptome comparisons between apomictic and closely related sexual individuals from reproductive tissues at different developmental stages have uncovered pathways potentially central to apomixis including protein degradation, transcription, stress response, and cell-to-cell signaling (Albertini et al 2005;Laspina et al 2008;Sharbel et al 2010;Silveira et al 2012;Okada et al 2013).…”

Development of a modified transformation platform for apomixis candidate genes research in Paspalum notatum (bahiagrass)

“…To date, plant genetic transformation has not been explored as a tool to facilitate harnessing apomixis for the benefit of agriculture. While in the past few years dozens of genes differentially expressed during sexual and apomictic development Chen et al 1999;Albertini et al 2004;Cervigni et al 2008;Laspina et al 2008) or positionally linked to apomixis (Calderini et al 2006;Conner et al 2008;Podio et al 2012) have been identified, functional studies have been performed only on randomly generated mutants originated from model sexual species.…”