The Arabidopsis BELL1 and KNOX TALE homeodomain proteins interact through a domain conserved between plants and animals

Interactions between TALE (three-amino acid loop extension) homeodomain pro teins play important roles in the development of both fungi and animals. Al though in plants, two different subclasses of TALE proteins include importa nt developmental regulators, the existence of interactions between plant TA LE proteins has remained unexplored. We have used the yeast two-hybrid syst em to demonstrate that the Arabidopsis BELL1 (BEL1) homeodomain protein can selectively heterodimerize with specific KNAT homeodomain proteins. Intera ction is mediated by BEL1 sequences N terminal to the homeodomain and KNAT sequences including the MEINOX domain. These findings validate the hypothes is that the MEINOX domain has been conserved between plants and animals as an interaction domain for developmental regulators. In yeast, BEL1 and KNAT proteins can activate transcription only as a heterodimeric complex, sugge sting a role for such complexes in planta. Finally, overlapping patterns of BEL1 and SHOOT MERISTEMLESS (STM) expression within the inflorescence meri stem suggest a role for the BEL1-STM complex in maintaining the indetermina cy of the inflorescence meristem.