Transcriptome analysis during seed development in Paspalum notatum

FELITTI, S.A.; ACUÑA, C.A.; QUARIN, C.

Rosario

Congreso; 4to. Congreso Argentino de Bioinformática y Biología Computacional (4CAB2C) y 4ta. Conferencia Internacional de la Sociedad Iberoamericana de Bioinformática (SolBio); 2013

CIFASIS

Background The seed developmental process involves various tissues with several ploidy levels and different genetic origins. Therefore, its characterization at the transcriptome level is certainly a challenge. The hypothesis of endosperm balance number (EBN) postulates that each species has an effective number which may not necessarily be a direct reflection of its ploidy level [1], and it is important for normal endosperm and seed development to occur. An understanding of the formation of endosperm in apomicts is crucial for the perspective of transferring apomixis (asexual reproduction through seeds) to species of agronomic interest. Quarin [2] investigated the effect of different sources and ploidy levels of pollen on endosperm formation and seed production in aposporous tetraploid Paspalum notatum. Quarin concluded that since sexual Paspalum plants fit the EBN premise, the EBN insensitivity observed in apomictic plants might be a requirement for the spread of pseudogamous apomixis. Our hypothesis is that there are differences in the transcriptomes of ovaries of apomictic and sexual plants when pollination occurs and during the first hours of endosperm development.   Materials and Methods Experimental crosses using several races of P. notatum were made in order to induce the development of seeds with different combinations of maternal/paternal genomic ratios in the endosperm. Ovaries were isolated at different times after pollination, and the transcriptome characterization was performed using cDNA-AFLP methodology [3, 4].   Results and Discussion Differentially expressed transcript-derived fragments (TDFs) were selected by comparing five to seven crosses per gel. A total of 423 bands were isolated and PCR re-amplified. Out of them, 116 TDFs were successfully sequenced and sorted into 24 functional categories. Only 17 TDFs displayed differential expression patterns specifically associated with the formation or abortion of seeds. Among these, 2 transcripts were associated with the organization of the cytoskeleton and 1 with the plant cell wall. Since the endosperm undergoes a brief and highly specialized pattern of development involving cell and microtubule cycles, and specific ways of wall placement, these genes could be interesting candidates for further analysis. Also, it is worth mentioning that 4 transcripts were predicted to be involved in amino acid and protein metabolism and transport. One of these TDFs presented 67% identity with a maize protein disulfide isomerase. Protein disulfide isomerases play important roles in the maturation of secreted or plasma membrane proteins. Wang et al. [5] demonstrated that certain T-DNA insertions in A. thaliana PDIL2-1, a protein disulfide isomerase (PDI), have reduced seed set, due to delays in embryo sac maturation. Moreover, results suggested that these truncated versions of PDIL2-1 function in sporophytic tissues to affect ovule structure and impede embryo sac development, thereby disrupting pollen tube guidance. This transcript was found in pollinated ovaries of P. notatum that completed the development of seeds, reinforcing the idea that pollen tube guidance and fertilization of the central cell are essential for endosperm development in this species.