Final Report Summary - FLOWERING CHROMATIN (Control of flowering time by chromatin remodelling) A fascinating aspect of plant development and an economically very important trait is the switch from vegetative to reproductive development. Flowering time is the most studied developmental transition in plants and our molecular understanding of the genetic pathways regulating flowering time has explained the physiological characteristics that have intrigued biologists for over a century. Many flowering time genetic screens have identified a series of chromatin activities conserved among most complex organisms. The study of these conserved chromatin factors are not only relevant for plant development but for human cells as well because their misregulation is often associated with diseases such as cancer. The aim of this project is to study the interplay between SWR1 and NuA4 chromatin remodelling complexes in the control of flowering time. These complexes share some components like SWC4 and YAF9 proteins. Genes encoding for these two proteins are conserved in most eukaryotes, and Arabidopsis thaliana genome presents one gene encoding for SWC4 and the two YAF9 homologs, YAF9A and YAF9B. Therefore, to understand the interplay between SWR1-C and NuA4-C in flowering time, we studied in detail the Arabidopsis SWC4 and YAF9 genes using a combination of molecular genetics, chromatin biology and biochemical approaches. By proteomic studies we found that AtSWC4 and AtYAF9 proteins are bona fide components of the Arabidopsis SWR1 complex. Phenotypic characterization and genetic analyses of loss-of function mutant lines revealed that AtSWC4 and AtYAF9 regulate flowering altering the expression of floral master genes. Molecular characterization and histone modifications analyses defined a novel regulatory mechanism of plant gene expression by H2AZ deposition. The comprehensive understanding of the fundamentals of flowering time obtained in this project will allow enhancement of crop performance by modulating flowering time trait at the molecular level and will thus be of great value to address the problems of food security that our society will be facing with the postulated global climate changes ahead.
