Although much is known about seed and fruit development at the molecular level, many gaps remain in our understanding of how cell wall modifications can impact developmental processes in plants, as well as how biomechanical alterations influence seed and fruit growth. Mutants of Arabidopsis thaliana constitute an excellent tool to study the function of gene families devoted to cell wall biogenesis. We have characterized a collection of lines carrying mutations in representative cell wall-related genes for seed and fruit size developmental defects, as well as altered germination rates. We have linked these studies to cell wall composition and structure. Interestingly, we have found that disruption of genes involved in pectin maturation and hemicellulose deposition strongly influence germination dynamics. Finally, we focused on two transcriptional regulators, SEEDSTICK (STK) and LEUNIG-HOMOLOG (LUH), which positively regulate seed growth. Herein, we demonstrate that these factors regulate specific aspects of cell wall properties such as pectin distribution. We propose a model wherein changes in seed coat structure due to alterations in the xyloglucan-cellulose matrix deposition and pectin maturation are critical for organ growth and germination. The results demonstrate the importance of cell wall properties and remodeling of polysaccharides as major factors responsible for seed development.

In gymnosperms such as Ginkgo biloba, the pollen's arrival plays a key role in ovule development, before fertilization occurs. Accordingly, G. biloba female plants geographically isolated from male plants aborted all their ovules after the pollination drop emission, which is the event that allows the ovule to capture pollen grains. To decipher the mechanism induced by pollination required to avoid ovule senescence and then abortion, we compared the transcriptomic of pollinated and unpollinated ovules at three time points after the end of the emission of pollination drops. Transcriptomic and in situ expression analyses revealed that several key genes involved in programmed cell death such as senescence and apoptosis, DNA replication, and cell cycle were differentially expressed in unpollinated ovules compared to pollinated ones. Interestingly, we provided evidence that the pollen captured by the pollination drop affects auxin local accumulation and might cause the deregulation of key genes required for ovule's programmed cell death and activating both the cell cycle and DNA replication genes.

Successful seed development in angiosperms depends on the coordinated transport and allocation of sugars from maternal tissues to the developing embryo and endosperm. In Arabidopsis thaliana , ovules function as carbohydrate sink organs, accumulating starch in both gametophytic and sporophytic domains prior to fertilization. This stored starch is later mobilized to support early embryogenesis. Despite extensive knowledge of starch metabolism in photosynthetic tissues, the regulatory mechanisms governing sugar transport in reproductive organs remain poorly understood. Recent studies have identified fertilization-dependent changes in nutrient flow, including callose-mediated modulation of symplastic transport at the phloem unloading site. However, the molecular players orchestrating these transitions are largely unknown. Here, we show that the MIKC MADS domain transcription factors ABS/TT16 and STK play critical roles in regulating maternal nutrient flow during ovule maturation and seed development. We dissect their functional redundancy using omics and genetic approaches, underscoring the importance of different ovule tissues in coordinating sugar transport pathways for post-fertilization development. Our findings reveal a previously underappreciated layer of genetic control over nutrient allocation in reproductive tissues and provide new insights into the metabolic reprogramming required for successful seed formation.

In angiosperms, ovule development requires the activity of the C, D and E classes of MADS genes, which encode key transcriptional regulators of reproductive development. The SEPALLATA (SEP) MADS transcription factors (MTFs), which belong to the E class, act as organizing hubs of MADS heterotetrameric complexes and play an essential role in the development of flower organs. However, the role of the SEP genes in ovule and seed development has been difficult to determine due to redundancy in the subclade, the lack of observable phenotypes in single and double sep1 sep2 mutants and the homeotic conversion of the carpel into sepal or leaf in higher order sep mutants. Here, we engineered a version of SEP3 ( SEP3 ^ΔM ) that encodes a protein lacking the DNA-binding MADS-domain but retains the oligomerization domains needed for MADS protein heterotetramerization. In vitro experiments demonstrated the ability of SEP3 ^ΔM to interact with the C and D classes of MTF, reducing the capability of such MADS complex to efficiently bind DNA. sep3 ^ΔM plants showed a delay in flower opening and organ maturation and a reduced fertility. The ovules exhibited reduced outer integument growth, and the few seeds that developed showed impaired mucilage secretion upon imbibition. RNA-seq analysis of sep3 ^ΔM demonstrated misregulation of genes involved in outer integument and seed coat development. Taken together, these data indicate the key role of SEP3-containing MADS complexes in proper ovule outer integument growth and seed coat development.