C-ABI3, THE CARROT HOMOLOG OF THE ARABIDOPSIS ABI3, IS EXPRESSED DURING BOTH ZYGOTIC AND SOMATIC EMBRYOGENESIS AND FUNCTIONS IN THE REGULATION OF EMBRYO-SPECIFIC ABA-INDUCIBLE GENES

A carrot gene homologous to the ABI3 gene of Arabidopsis was isolated from a carrot somatic embryo cDNA library and designated C-ABI3. The s equence of C-ABI3 was very similar to those of ABI3 of Arabidopsis and VPI of maize in certain conserved regions. The expression of C-ABI3 w as detected specifically in embryogenic cells, somatic embryos and dev eloping seeds. Thus, expression of C-ABI3 was limited to tissues that acquired desiccation tolerance in response to endogenous or exogenous abscisic acid (ABA). Endogenous levels of ABA in seeds increased trans iently and then desiccation of seeds started. The expression of C-ABI3 in developing seeds was observed prior to the increase in levels of e ndogenous ABA that was followed by desiccation of seeds. In transgenic mature leaves in which C-ABI3 was ectopically expressed, expression o f ECP31, ECP63 and ECP40 was induced by treatment with ABA, which indi cates that the expression of ECP genes was controlled by the pathway(s ) that involved C-ABI3 and ABA. This suggests that C-ABI3 has the same function as VP1/ABI3 factor in carrot somatic embryos.