Maize endosperm secretes a novel antifungal protein into adjacent maternaltissue

A series of endosperm transfer layer-specific transcripts has been identifi ed in maize by differential screening of a cDNA library of transcripts at 1 0 days after pollination. Sequence comparisons revealed among this class of cDNAs a novel, small gene family of highly diverged sequences encoding bas al layer antifungal proteins (BAPs). The bap genes mapped to two loci on ch romosomes 4 and 10. So far, bap-homologous sequences have been detected onl y in maize, teosinte and sorghum, and are not present in grasses outside th e Andropogoneae tribe. BAP2 is synthesized as a pre-proprotein, and is proc essed by successive removal of a signal peptide and a 29-residue prodomain. The proprotein can be detected exclusively in microsomal membrane-containi ng fractions of kernel extracts. Immunolocalization reveals BAP2 to be pred ominantly located in the placentochalazal cells of the pedicel, adjacent to the basal endosperm transfer layer (BETL) cells, although the BAPS transcr ipt is found only in the BETL cells. The biological roles of BAP2 propeptid e and mature peptide have been investigated by heterologous expression of t he proprotein in Escherichia coil, and by tests of its fungistatic activity and that of the fully processed form in vitro. The mature BAP2 peptide exh ibits potent broad-range activity against a range of filamentous fungi, inc luding several plant pathogens.