The research in Dr. Yanofsky's lab focuses on the molecular mechanisms which control the initiation and development of flowers and fruits in higher plants, with particular emphasis on the model system of Arabidopsis. Our recent studies of flower development have uncovered important new regulators of flower organ identity, including the three SEPALLATA MADS-box genes that act redundantly to specify the identity of petals, stamens and carpels. Our current efforts are focused on studying the interactions between the SEPALLATA genes with other organ identity genes and on identifying their direct downstream targets.
Much of our recent research has focused on fruit development, which is arguably the most complex plant organ. Arabidopsis fruit, which are derived from the fertilized gynoecium (carpels), consist of a number of distinct tissue types, including the valves, replum and dehiscence zone. The dehiscence zone consists of a narrow band of cells that extends along the entire length of the fruit. Upon fruit maturation, cell separation within the dehiscence zone allows the valves to detach from the replum and for the seeds to be dispersed. We have shown that the SHATTERPROOF1 (SHP1) and SHP2 MADS-box genes act redundantly to specify dehiscence zone cell fate. The SHP genes act to promote the expression of the INDEHISCENT bHLH gene, which is also required for dehiscence zone differentiation. Because the dehiscence zone fails to differentiate in these mutants, the fruits fail to open and the seeds cannot be dispersed through their normal mechanism. We have also shown that the FRUITFULL MADS-box gene is required for the post-fertilization elongation of the fruit and is required for valve cell differentiation. Interestingly, the FRUITFULL gene product negatively regulates the SHP and IND genes such that the SHP and IND genes are ectopically expressed in fruitfull mutant valves. More recently, we have shown that the REPLUMLESS gene is required for formation of the replum. These studies have allowed us to begin to build a framework for the regulatory interactions that underlie fruit development in Arabidopsis.
The past decade has revealed rapid progress toward identifying the major genes controlling flower organ identity and formation of the different parts of the fruit. However, almost nothing is currently known about the differentiation of specific cell types within organs. Our future research will focus on identifying the cascade of gene activity that ultimately leads to differentiation of individual cell types within organs.