The Maize (Zea mays L.) Cat1 Catalase Promoter Displays Differential Binding of Nuclear Proteins Isolated from Germinated and Developing Embryos and from Embryos Grown in the Presence and Absence of Abscisic Acid

We previously demonstrated that amounts of Cat1 RNA in developing immature maize (Zea mays L.) embryos change in parallel with endogenous abscisic acid (ABA) content. In excised immature embryos, addition of ABA leads to a large increase in Cat1 RNA accumulation. The Cat1 transcript, however, also accumulates to high amounts in scutella of germinating embryos, where ABA content is low and decreasing. Here we show that application of ABA to germinated embryos no longer results in the up-regulation of the Cat1 transcript accumulation that is seen during embryogenesis. This suggests that factors other than ABA control Cat1 expression at this developmental stage. Using band-shift and southwestern analyses, we show that the change in sensitivity to ABA is paralleled by changes in nuclear proteins binding to a 28-bp region of the Cat1 promoter in vitro. One protein (CAT1BP-20) shows increased accumulation in the absence of ABA, suggesting that a repressor-mediated mechanism accounts for at least a portion of the ABA regulation of Cat1.