Does barley inhibit its own alpha-amylase to defend against pathogens?

The bifunctional alpha-amylase subtilisin inhibitor (BASI) from barley is a bifunctional protein with roles in inhibition of proteases and of endogenous alpha-amylase. The subtilisin inhibitor activity has been attributed to a defence role for this protein in barley. The specific inhibition of barley alpha-amylases by this protein has been previously explained as a role associated with the control of starch mobilisation in germinating cereals. It has long been assumed that this protein was expressed in aleurone and endosperm of barley. We recently isolated the promoter of the asi gene and demonstrated pericarp specific expression of GFP with this promoter. Expression of this gene specifically in the pericarp of developing barley suggests that the protein is primarily associated with defence of the seed against pathogens. The action of the protein in specifically inhibiting barley alpha-amylase may be associated with denial of fungal access to seed starch reserves.