The underlying processes governing seed size plasticity: Impact of endoploidy on seed coat development and cell expansion in <em>Medicago truncatula</em>

Abstract Bigger seeds represent an agronomic and economic benefit but the breeding and ecological balance between seed size and number is difficult to find. Large seeds associated with other practices can improve crop competitiveness as they are more vigorous and result in healthier crops with higher yields, even under stressful conditions. Applying genomic research and genome-wide association studies to breeding is generating new strategies to improve seed traits and novel insights into the biology of seed development and metabolism that are discussed in this chapter. The DNA amount differs among the seed tissues and amplifying genomic DNA by endocycle induction and endoreduplication can play a role in the phenotypic plasticity of seed development and size. Such phenomena are probably controlled by cell expansion and thereby also determine final cell size. Changes in plant growth are associated with changes in seed mass, which in turn limit seed protein content and weight. The reasons why a seed has a definite development regardless of resources available remain unexplained but regulating seed size may be a solution to stabilize yield in many crops. A major question is to identify those genes that make seed setting and final seed size less susceptible to stress, given that both genetic and epigenetic regulations are modulated by the environment. Endopolyploidy is a factor controlling organ size, which raises new questions on its implication in cell expansion and opens up a new perspective to control final seed size. This could lead to finding solutions for an agroecological adaptation to adverse climatic changes.