XVI International Botanical Congess

In situ hybridisations have shown the developing maize endosperm to contain a series of domains of gene expression. One basal domain consists of transfer cells. A series of transfer layer-specific probes (BETL-1 to -x) of diverse function have been isolated, which are coordinately expressed during endosperm development and turn over well before kernel maturity. In addition to genes involved in assimilate transfer, three classes of small cysteine-rich proteins with putative roles in pathogen defence, and a Myb-related transcriptional regulator, were identified as BETL genes. The expression of these genes is differentially reduced in rgf, a novel mutant severely reducing grain filling. The promoters of two BETL genes direct transfer cell-specific expression in transgenic maize, thus providing a tool to determine the contribution of the transfer layer to grain filling.