Abstract
Legume seeds are important as protein and oil source for human diet. Understanding how their final seed size is determined is crucial to improve crop yield. In this study, we analyzed seed development of three accessions of the model legume, Medicago truncatula, displaying contrasted seed size. By comparing two large seed accessions to the reference accession A17, we described mechanisms associated with large seed size determination and potential factors modulating the final seed size. We observed that early events during embryogenesis had a major impact on final seed size and a delayed heart stage embryo development resulted to large seeds. We also observed that the difference in seed growth rate was mainly due to a difference in embryo cell number, implicating a role of cell division rate. Large seed accessions could be explained by an extended period of cell division due to a longer embryogenesis phase. According to our observations and recent reports, we observed that auxin (IAA) and abscisic acid (ABA) ratio could be a key determinant of cell division regulation at the end of embryogenesis. Overall, our study highlights that timing of events occurring during early seed development play decisive role for final seed size determination.
Highlights
Increasing seed yield has been one of the major objectives for plant biologists in the last decades
We focused on the events occurring during the seed development leading to seed size determination, without investigating remobilization processes from plant to seed that potentially lead to change in seed number
In dicot seeds such as those of legumes, the volume is mostly made up of cotyledons and it has been shown that cell number and size of cotyledon cells are directly associated to final seed size [28]
Summary
Increasing seed yield has been one of the major objectives for plant biologists in the last decades. The embryogenesis is a morphogenetic process, tightly regulated by a genetic program that will define the final number of cell During this process, the zygote will undergo series of cell division, which will lead to different developmental stages of the embryo, (i.e., globular, heart, torpedo, bent cotyledon and mature embryo) [5]. During domestication, seed size was a major determinant of seed yield and a large variation of this trait still exists within species. We used the genetic variability of three different Medicago accessions to decipher the differences between normal and larger seeds We analyzed both the mature and developing seeds in terms of growth pattern, embryo development, cell expansion, cell proliferation and hormonal homeostasis
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