Transcriptome analysis of seed development in apomictic Paspalum notatum

Abstract

The seed developmental process involves various tissues with several ploidy levels and different genetic origins. Therefore, its characterisation at the transcriptome level is certainly a challenge. The hypothesis of endosperm balance number (EBN) postulates that each species has an effective number that is important for normal endosperm and seed development to occur. Understanding endosperm formation in apomictic plants is crucial for the perspective of transferring apomixis to sexual species of agronomic interest. Since sexual tetraploid Paspalum plants fit the EBN premise, the EBN insensitivity observed in apomictic plants might be a requirement for the spread of pseudogamous apomixis. Crosses using several cytotypes of Paspalum notatum were made in order to induce the development of seeds with different maternal/paternal genomic ratios in the endosperm. A transcriptome characterisation of ovaries 3 h after pollination was performed using cDNA-AFLP methodology. Forty-six of the 100 differentially expressed transcript-derived fragments (DETDFs) were specifically found in crosses in which apomictic plants were used as the female parent and presented a predicted m : p ratio in the endosperm that was different to the 2:1 requirement of the EBN. Moreover, 12 of the DETDFs presented identity with proteins that were differentially expressed in response to changes in the levels of extracellular ATP (eATP) in Arabidopsis cell suspension cultures. eATP is an important molecular switch in plants that tightly controls organellar energy metabolism and activates gene expression controlling specific growth and developmental programmes. The results suggest that eATP-mediated signalling could be involved in the regulation of endosperm development.

Identification of Genes Related to Endosperm Balance Number Insensitivity in Paspalum notatum

“…The classification of transcripts in this study was similar to the functional categories proposed in the analysis corresponding to 3 h after pollination (Felitti et al, 2015). In that case, the 100 DETDFs identified were classified in 12 functional categories.…”

“…The beads were collected again using the magnet, and the supernatant was transferred to a new tube containing the template fragments for the adaptor ligation. The sequences of primers and adapters used for cDNA‐AFLP analyses were described by Felitti et al (2015).…”

How to Become an Apomixis Model: The Multifaceted Case of Paspalum

“…A second transcriptome analysis using the same methodology revealed 65 new transcripts differentially expressed at the premeiosis/meiosis stage [ 58 ], including members of the LORELEI family ( GAP1 ) [ 58 , 96 ], the S-adenosyl-L-methionine-dependent methyltransferase family ( TRIMETHYLGUANOSINE SYNTHASE1 ) [ 58 , 97 ]; the MAP3K YODA family ( QUI-GON JINN [ 58 , 98 ] as well as several retrotransposons carrying transduplicated gene segments [ 58 , 99 ], sometimes involving apomixis-associated genes like SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE ( SERK ) [ 58 , 99 , 100 ], and long-noncoding transcripts possibly involved in splicing regulation [ 101 ]. Furthermore, differential expression analyses during early seed development (3–24 h after pollination) revealed ≈100 DETs possibly associated with the unbalanced genomic contribution found in pseudogamous endosperms (4:1), including transcripts related with transcription regulation, signal transduction (e.g., lectin-like protein kinase and CK2 protein kinase α 1), growth/division, and response to changes in the extracellular ATP levels [ 102 , 103 ].…”

Endosperm variability: from endoreduplication within a seed to higher ploidy across species, and its competence

“…For example, Tripsacum with diploids and tetraploids reported to exhibit genome dosage (maternal to paternal) of 8:1 and 8:2 ratios in apomictic plants, but 2:1, 4:1 and 4:2 ratios observed in sexual plants (Grimanelli et al, 1997). Paspalum with di-, tri-, tetra-, penta-, hexa- and octaploid species, the endosperm genome dosage level varies widely from 1:1, 2:1, 3:1, 4:1, 4:3, 8:1 to 8:3, with 4:1 genome dosage exhibiting the maximum reproductive efficiency (Burton, 1948; Quarin et al, 1984; Quarin, 1999; Ortiz et al, 2013; Felitti et al, 2015). An AFLP Marker associated with apomictic trait loci in Paspalum has been identified (Labombarda et al, 2002), its cross-transferability in other related species might be of advantage in differentiating the apomictic from sexual plants.…”

“…Exceptionally, the occurrence of pseudogamy resulting in the normal EBN genome dosage level of 2:1 is possible only when the reduced sperm cell is fused with the central cell containing a single unreduced polar nucleus as reported in Panicum maximum (Warmke, 1954). However, in general, due to pseudogamy, 4:1 is formed when the two unreduced polar nuclei are fused with one reduced sperm nucleus (Grimanelli et al, 1997; Quarin, 1999; Felitti et al, 2015). Polyploidy and apomixis are reported to be strongly associated, although gametophytic apomixis is reported in diploids (Sharbel et al, 2009; Ortiz et al, 2013).…”