6533b82afe1ef96bd128b519

RESEARCH PRODUCT

Impact of endopolyploidy on seed coat development and cell expansion in Medicago truncatula

subject

description

Growth of the seed coat is regulated by genetic interactions between maternal and filial tissues that ultimately establish seed size. However, endopolyploidy is one of the welldocumented factors controlling organ size. During seed development, the arrest of cell division at 4 DAP in the expanding seed coat is compensated for by cell elongation. Thus, the ploidy status of seed coat nuclei was assessed in order to determine if there is any correlation of endopolyploidy with cell elongation. In 10 DAP seed sections, the DAPI-integrated fluorescence, which correlates to DNA quantity, was measured in the seed coat parenchyma nuclei using the diploid embryo nuclei as internal control. Significantly higher fluorescence values were obtained in seed coat nuclei, suggesting a higher DNA content. The high proportion of genes annotated as involved in nucleotide metabolism supports also the initiation of endocycles. At this stage, cell divisions were not detected in the seed coat, but cell elongation was initiated and may be correlated to the induction of endopolyploidy. This positive correlation between ploidy level and cell size in M. truncatula seed coat was validated using flow cytometry analysis at different stages of seed development (from 8 to 20 DAP). This study opens up a new perspective to control final seed size. Moreover, it raised new questions concerning the implication of endopolyploidy in cell expansion.