Abstract
BackgroundPaspalum notatum Flügge is a subtropical grass native to South America, which includes sexual diploid and apomictic polyploid biotypes. In the past decade, a number of apomixis-associated genes were discovered in this species through genetic mapping and differential expression surveys. However, the scarce information on Paspalum sequences available in public databanks limited annotations and functional predictions for these candidates.ResultsWe used a long-read 454/Roche FLX+ sequencing strategy to produce robust reference transcriptome datasets from florets of sexual and apomictic Paspalum notatum genotypes and delivered a list of transcripts showing differential representation in both reproductive types. Raw data originated from floral samples collected from premeiosis to anthesis was assembled in three libraries: i) sexual (SEX), ii) apomictic (APO) and iii) global (SEX + APO). A group of physically-supported Paspalum mRNA and EST sequences matched with high level of confidence to both sexual and apomictic libraries. A preliminary trial allowed discovery of the whole set of putative alleles/paralogs corresponding to 23 previously identified apomixis-associated candidate genes. Moreover, a list of 3,732 transcripts and several co-expression and protein –protein interaction networks associated with apomixis were identified.ConclusionsThe use of the 454/Roche FLX+ transcriptome database will allow the detailed characterization of floral alleles/paralogs of apomixis candidate genes identified in prior and future work. Moreover, it was used to reveal additional candidate genes differentially represented in apomictic and sexual flowers. Gene ontology (GO) analyses of this set of transcripts indicated that the main molecular pathways altered in the apomictic genotype correspond to specific biological processes, like biotic and abiotic stress responses, growth, development, cell death and senescence. This data collection will be of interest to the plant reproduction research community and, particularly, to Paspalum breeding projects.
Highlights
Paspalum notatum Flügge is a subtropical grass native to South America, which includes sexual diploid and apomictic polyploid biotypes
2,066 were overexpressed in the apomictic plant, while 1,666 were upregulated in the sexual plant. These results suggest that numerous genes poorly expressed or silent during sexual reproduction are transcriptionally activated in ovules of apomictic plants
The database may allow the recovery of allele/splice variants corresponding to dozens of apomixis and ploidy response candidate genes that had been identified and verified in prior works through Polymerase chain reaction (PCR)-based approaches [45, 48, 53, 67]
Summary
Paspalum notatum Flügge is a subtropical grass native to South America, which includes sexual diploid and apomictic polyploid biotypes. Apomixis (i.e. asexual reproduction via seeds) is an intriguing developmental strategy described in more than 400 angiosperm species [1], which results from gaining the ability to bypass the fundamental aspects of sexual reproduction: meiosis and fertilization [2]. Apomixis involves the combination of three fundamental events: lack or failure of meiosis (apomeiosis); fertilization-independent. A few somatic (2n) cells surrounding the reduced megagametophyte differentiate and form multiple globular-shaped embryos, which develop to maturity. In gametophytic apomicts, unreduced (2n) embryo sacs are formed in the ovule nucellus after a series of mitosis. The formation of these unreduced megagametophytes can follow two mechanistic types, i. Embryo development is fertilization independent, whereas endosperm formation may or may not require fertilization [2, 6]
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