Expression of a Group 3 LEA Protein During Maturation of Zo

approved: aA'L I Several different types of proteins that are modulated by abscisic acid (ABA) accumulate in developing embryos of maize (Zeamays L). Some of these proteins are specific to the developing seed, such as the storage globulin, GLB1, while others are involved in general responses to water deficit. Here, I report the isolation and characterization of a very distinct family of proteins, named MLG3. MLG3 (Maize Lea Group 3) are low molecular weight proteins that become abundant around the onset of desiccation tolerance in maize embryos. Like other proteins of this class, MLG3 polypeptides are ABA-responsive. They are found in maturing seeds and in dehydrating plant tissues. Antigenically related proteins are found in other cereals. MLG3 proteins decline in abundance after germination, but increasing levels accumulate when seedlings are grown under conditions of water stress. To distinguish the regulation of developmentallyprogrammed ABA responses from those that are environmentally induced, a comparison was made between the ontological pattern and accumulation requirements of MLG3 polypeptides and the previously described results for GLB1 protein. GLB1 accumulation begins early in maturation phase and specifically requires high levels of ABA and the Redacted for Privacy participation of the Viviparous-I(VPI) gene product. VPI is required for other ABA-modulated events in maize seed development as well. Experiments using vpi mutants and mutants deficient in ABA synthesis (vp5 mutation), show that MLG3 accumulation also is dependent upon ABA, but it occurs much later in embryogenesis, coincident with the onset of dehydration. In contrast to GLB1, MLG3 proteins can be induced by denovo ABA synthesis in response to culturing in high osmoticum, and MLG3 has no specific requirement for the