VAAMANA—a BEL1-like homeodomain protein, interacts with KNOX proteins BP and STM and regulates inflorescence stem growth in Arabidopsis

Plant shoot growth depends on the activity of the shoot apical meristem (SAM), where organ primordia are initiated. In turn, the function of the SAM depends on the activities of homeodomain (HD) proteins of the knotted1-like homeobox (KNOX) class [Long et al., Nature 379 (1996) 66; Vollbrecht et al., Development 127 (2000) 3161]. In plants, KNOX proteins have been shown to interact specifically with the BEL1-like (BELL) class of homeodomain proteins [Bellaoui et al., Plant Cell 13 (2001) 2455; Muller et al., Plant 27 (2001) 13; Smith et al., Proc. Natl. Acad. Sci. USA 99 (2002) 9579], through a domain conserved between plants and animals. We have isolated a mutation in a BELL homeobox gene VAAMANA (VAN) that causes a dwarf phenotype. In addition, van inflorescence stems have clusters of cauline leaves; typically three are produced at each node. VAN interacts specifically with the class I KNOX proteins SHOOTMERISTEMLESS (STM), BREVIPEDICELLUS (BP), and KNAT6 (K6), and nuclear localisation of a VAN-GFP fusion depends on co-expression of STM or BP in tobacco leaves. This suggests that localisation of VAN, like that of the animal PBC homeodomain protein [Rieckhof et al., Cell 91 (1997) 171; Berthelsen et al., Genes Dev. 13 (1999) 946], is also regulated by interaction with a partner homeodomain protein.