OVULE AND EMBRYO DEVELOPMENT IN ARABIDOPSIS
Embryogenesis begins after ovule fertilization when the zygote undergoes cell division to establish the apical and basal embryo and then continues with specialized cell divisions until a mature embryo is formed. Inhibitor and genetic studies have shown that auxin gradients contribute to both ovule and embryo development. The Arabidopsis thaliana protein APM1 is an M1 metaloprotease that has affinity for and catalyzes the hydrolysis of the auxin transport inhibitor naphthylphthalmic acid. Peer et al. (pages 1693–1721) show that, in addition to embryonic patterning defects, apm1 loss-of-function alleles exhibit distinct seedling lethal phenotypes caused by premature determinacy of the primary root meristem. The cover image shows four ovules in a silique from an apm1-1 heterozygous plant as well as a pollen tube in the top right corner. The two synergid cells, an egg cell, and two polar nuclei are visible in the center left ovule.