The surfaces of land plants are covered with a cuticle that is essential for retention of water.  Epidermal surfaces of Arabidopsis thaliana embryos and juvenile plants that were homozygous for abnormal leaf shape1 (ale1) mutations were defective, resulting in excessive water loss and organ fusion in young plants.  In ale1 embryos, the cuticle was rudimentary and remnants of the endosperm remained attached to developing embryos.  Juvenile plants had a similar abnormal cuticle.  The ALE1 gene was isolated using a transposon-tagged allele ale1-1.  The predicted ALE1 amino acid sequence was homologous to those of subtilisin-like serine proteases.  The ALE1 gene was expressed within certain endosperm cells adjacent to the embryo and within the young embryo.  Expression was not detected after germination.  Our results suggest that the putative protease ALE1 affects the formation of cuticle on embryos and juvenile plants and that an appropriate cuticle is required for separation of the endosperm from the embryo and for prevention of organ fusion.
 
 

Figure The phenotype generated by abnormal-leaf-shape1 (ale1) mutation and the site of expression of the ALE1 gene Gross morphology of aerial parts of wild-type (A) and ale1 (B) plants that were grown on soil.  (C) Transverse section of fused leaves of ale1.  (D and E) Transmission electron micrographs of epidermal surfaces of wild-type (D) and ale1 (E) cotyledons.  (F) analysis of a heart-stage embryo and cellularized endosperm by in situ hybridization with an antisense probe of ALE1.  Strong signals (dark coloration) were observed in some of the cellularized endosperm that surrounded the embryo.  (G) GUS activity in endosperm cells of a transgenic plant that harbored the ALE1 promoter-GUS fusion gene.  Scale bars, 50 mm.