FLOR1, a putative interaction partner of the floral homeotic protein AGAMOUS, is a plant-specific intracellular LRR

FLOR1 is a flower-specific leucine-rich repeat (LRR) protein that interacts in vitro with the MADS box protein AGAMOUS. However, FLOR1 belongs to the plant-specific (PS) subfamily of LRR proteins which are thought to be extracellular based on immunolocalization experiments with one of them and the presence of a hydrophobic signal peptide in the N-terminus of all of them. As a first step towards exploring the possible in vivo role of the AG-FLOR1 interaction, we show here that FLOR1 mRNA in wild type Arabidopsis thaliana is specific to inflorescence, meristems, floral meristems, stamens and carpels with a spatio-temporal mRNA expression pattern during flower development that is similar to that of AGAMOUS. To confirm FLOR1 transcription expression in meristems, stamens and carpels, its mRNA pattern of expression was studied in mutants of floral meristem or floral organ identity genes (LEAFY, APETALA 1, CAULIFLOWER, AGL8, APETALA2, and APETALA3). Furthermore, immunolocalization experiments show that the FLOR1 transcript and protein have similar expression patterns. Light and electron micrographs of immunolocalization experiments, as well as GFP cellular localization in transgenic A. thaliana lines expressing FLOR1-GFP chimeric proteins suggest that FLOR1 is localized in the cytoplasm and nucleus inside cells. These results contrast with previous reports that suggest that other members of the same PS LRR subfamily are only localized in the extracellular space. The functional relevance of our findings in terms of the possible in vivo interaction of FLOR1 and AGAMOUS are discussed. (C) 2004 Elsevier Ireland Ltd. All rights reserved.