Chromatin Remodelling in Plant Development

Patterning of the floral organs is exquisitely controlled and executed by floral homeotic regulators. Inappropriate induction of these genes causes reduced reproductive fitness and is prevented by polycomb repression. At the onset of flower patterning this repression needs to be overcome to allow induction of the floral homeotic genes and formation of the floral organs. How this is achieved is not well understood. Our study revealed that the SWI2/SNF2 chromatin remodeling ATPases SPLAYED (SYD) and BRAHMA (BRM) are redundantly required for flower patterning and for the activation of the floral homeotic genes. The SWI2/SNF2 ATPases are recruited to the regulatory regions of the floral homeotic genes at the onset of flower development by two direct transcriptional activators of these genes. We further show that both SYD and BRM genetically act as a trithorax proteins and that the requirement for SYD and BRM in flower patterning can be overcome by partial loss of polycomb activity in curly leaf (clf) mutants. The combined data implicate the SWI2/SNF2 chromatin remodelers in reversal of polycomb repression to allow induction of the floral homeotic genes.