Expression patterns and protein structure of a lipid transfer protein END1 from Arabidopsis

Arabidopsis END1-LIKE (AtEND1) was identified as a homolog of the barley endosperm-specific gene END1 and provides a model for the study of this class of genes and their products. The END1 is expressed in the endosperm transfer cells (ETC) of grasses. The ETC are responsible for transfer of nutrients from maternal tissues to the developing endosperm. Identification of several ETC-specific genes encoding lipid transfer proteins (LTP), including the END1, provided excellent markers for identification of ETC during seed development. To understand how AtEND1 forms complexes with lipid molecules, a three-dimensional (3D) molecular model was generated and reconciled with AtEND1 function. The spatial and temporal expression patterns of AtEND1 were examined in transgenic Arabidopsis plants transformed with an AtEND1 promoter-GUS fusion construct. The AtEND1 promoter was found to be seed and pollen specific. In contrast to ETC-specific expression of homologous genes in wheat and barley, expression of AtEND1 is less specific. It was observed in ovules and a few gametophytic tissues. A series of AtEND1 promoter deletions fused to coding sequence (CDS) of the uidA were transformed in Arabidopsis and the promoter region responsible for AtEND1 expression was identified. A 163 bp fragment of the promoter was found to be sufficient for both spatial and temporal patterns of expression reflecting that of AtEND1. Our data suggest that AtEND1 could be used as a marker gene for gametophytic tissues and developing endosperm. The role of the gene is unclear but it may be involved in fertilization and/or endosperm cellularization.