AINTEGUMENTA homolog expression in Gnetum (gymnosperms) and implications for the evolution of ovulate axes in seed plants.

The expression of GpANTL1, a homolog of AINTEGUMENTA (ANT) found in the gymnosperm Gnetum parvifolium, was analyzed by RT-PCR and in situ hybridization. GpANTL1 was expressed in the leaf primordia, root tips, and young ovules. In the ovulate axis, expression was detected as four distinct rings around the outer, middle, and inner envelope primordia as well as around the nucellar tip. This pattern of expression is similar to that of ANT in Arabidopsis thaliana. A comparison of the expression of GpANTL1 with that of PtANTL1 in the conifer Pinus thunbergii suggests that the integrated expression of PtANTL1 may have been caused by congenital fusion of the integument, ovuliferous scale, and bract.