Promoter activity of ABI3 and of three LEA genes was monitored in Arabidopsis transgenics infected with Heterodera schachtii and Meloidogyne incognita. ABI3::GUS expression was induced (in four different promoter deletion constructs) during early infection stages with H. schachtii. Similar GUS expression patterns, though slightly later in time compared with ABI3, were observed for one of the LEA promoter constructs, whereas the other two were not induced by H. schachtii. Expression was mainly observed in the syncytia. In contrast, little or no reporter gene expression was observed upon infection with M. incognita. The data suggest a role for ABI3 during the formation and active growth of the syncytium and demonstrate a marked difference between syncytium and giant cell ontogenesis.