Lea proteins and survival in the dry state: lessons to be learned from proteome analyses in developing orthodox and recalcitrant seeds

Late embryogenesis abundant (LEA) proteins are highly hydrophilic, mainly intrinsically unordered proteins that accumulate during seed development. Their presence at high concentrations in mature seeds has led to the suggestion that they are part of the protective mechanisms associated with the survival in the dry state. However, there are a multitude of different LEA proteins whose expression is seed-specific and/or triggered by osmotic stress in desiccation-sensitive vegetative tissues. Comprehensive temporal studies on when and which LEA proteins appear during seed maturation is missing. Here, we address the question as to whether specific LEA proteins are linked to desiccation tolerance or survival during long term storage and which role they might play. By characterizing the heat soluble proteome of seeds of Medicago truncatula, the abundance of LEA proteins was monitored from seed filling to the maturation drying. We also compared the inventory of the LEA proteome with that of a recalcitrant legume species. Among the identified spots present in M. truncatula mature seeds corresponding to 16 LEA genes, we will show that there are sets of LEA proteins that are specifically associated with desiccation tolerance or seed longevity or maturation drying. Insights into their function will be provided by reverse genetics and in vitro experiments on recombinant proteins. We suggest that a panoply of LEA proteins are necessary to confer survival in the dry state because they exert specific and complementary protective roles that likely depends both on the target to be protected and the hydration level.