The seed-specific transactivator, ABI3, induces oleosin gene expression.
A microspore-derived cell suspension culture of Brassica napus was used as a host for expression studies involving seed oleosin genes. The suspension culture was previously shown to display biochemistry and gene expression typical of zygotic embryos. Using a biolistic, transient expression approach we demonstrate that the seed-specific activator ABI3 promotes oleosin gene expression in these cultures. Co-bombardment of an oleosin promoter-GUS fusion and a full-length ABI3 gene from Arabidopsis resulted in four to six-fold enhancement of GUS expression. Deletion analysis was performed to identify which oleosin upstream sequences were required for ABI3 regulation. These studies found that a truncated oleosin promoter containing 160 bp of 5' regulatory sequence was sufficient to confer ABI3 responsiveness. Mutation of a canonical abscisic acid response element within this 160 bp region had a dramatic effect on basal expression, reducing levels to 25% of control. However, this mutation had no significant effect on ABI3 transactivation, indicating that the reduction in basal oleosin expression was distinct from the ABI3 response. These results also suggest that ABI3-mediated transactivation occurs through either a less-conserved ABRE element or other abscisic acid-independent sequences within the minimal promoter. Together, these data provide the first direct evidence that ABI3 mediates oleosin transactivation.
Crowe
AJ
Department of Biological Sciences, University of Calgary, 2500 University Drive, NW, Calgary, Canada
Abenes
M
Plant
A
Moloney
MM