A MUTATION THAT ALLOWS ENDOSPERM DEVELOPMENT WITHOUT FERTILIZATION

The mechanisms that initiate reproductive development after fertilizat ion are not understood. Reproduction in higher plants is unique becaus e it is initiated by two fertilization events in the haploid female ga metophyte. One sperm nucleus fertilizes the egg to form the embryo. A second sperm nucleus fertilizes the central cell to form the endosperm , a unique tissue that supports the growth of the embryo. Fertilizatio n also activates maternal tissue differentiation, the ovule integument s form the seed coat, and the ovary forms the fruit. To investigate me chanisms that initiate reproductive development, a female-gametophytic mutation termed fie (fertilization-independent endosperm) has been is olated in Arabidopsis. The fie mutation specifically affects the centr al cell, allowing for replication of the central cell nucleus and endo sperm development without fertilization. The fie mutation does not app ear to affect the egg cell, suggesting that the processes that control the initiation of embryogenesis and endosperm development are differe nt. FIE/fie seed coat and fruit undergo fertilization-independent diff erentiation, which shows that the fie female gametophyte is the source of signals that activates sporophytic fruit and seed coat development . The mutant fie allele is not transmitted by the female gametophyte. Inheritance of the mutant fie allele by the female gametophyte results in embryo abortion, even when the pollen bears the wild-type FIE alle le. Thus, FIE carries out a novel, essential function for female repro ductive development.