The Genetic Control of SEEDSTICK and LEUNIG-HOMOLOG in Seed and Fruit Development: New Insights into Cell Wall Control

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.