Analysis of PEAM4, the pea AP1 functional homologue, supports a model for AP1-like genes controlling both floral meristem and floral organ identity in different plant species

APETALA1 (AP1) and its homologue SQUAMOSA (SQUA) are key regulatory genes s pecifying floral meristem identity in the model plants Arabidopsis and Anti rrhinum. Despite many similarities in their sequence, expression and functi ons, only AP1 appears to have the additional role of specifying sepal and p etal identity. No true AP1/SQUA-functional homologues from any other plant species have been functionally studied in detail, therefore the question of how the different functions of AP1-like genes are conserved between specie s has not been addressed. We have isolated and characterized PEAM4, the AP1 /SQUA-functional homologue from pea, a plant with a different floral morpho logy and inflorescence architecture to that of Arabidopsis or Antirrhinum. PEAM4 encodes for a polypeptide 76% identical to AP1, but lacks the C-termi nal prenylation motif, common to AP1 and SQUA, that has been suggested to c ontrol the activity of AP1. Nevertheless, constitutive expression of PEAM4 caused early flowering in tobacco and Arabidopsis. In Arabidopsis, PEAM4 al so caused inflorescence-to-flower transformations similar to constitutive A P1 expression, and was able to rescue the floral organ defects of the stron g ap1-1 mutant. Our results suggest that the control of both floral meriste m and floral organ identity by AP1 is not restricted to Arabidopsis, but is extended to species with diverse floral morphologies, such as pea.