The incorporation of H2A.
Z on to nucleosomes is mediated through the SWR1 complex in Arabidopsis that consists of proteins encoded by ACTIN-RELATED PROTEIN 6 (ARP6), SWC6 and PHOTOPERIOD-INDEPENDENT EARLY FLOWERING1 (PIE1) (Tasset, Yadav et al. 2018). Massive reprogramming of transcription-associated with cell differentiation during development involves activation and silencing of hundreds of genes (March-Diaz, Garcia-Dominguez et al. 2007). In plants, H2A.
Z has been implicated in the response to high temperature, the phosphate starvation response, osmotic stress, the immune response, floral induction, female meiosis, recombination, thalianol metabolism, and the regulation of microRNA abundance (Qin, Zhao et al. 2014, Xu, Leichty et al. 2018). This process requires extensive changes in chromatin structure as it has been evidenced by the identification of chromatin-remodeling factors whose mutation impairs normal development at many different levels (March-Diaz, Garcia-Dominguez et al.
2007). Three main biochemical mechanisms have been reported to alter chromatin structure. The first involves the posttranslational covalent modification of the amino- and carboxy-terminal tails of histones. The pattern of chemical modifications of histones within a nucleosome (acetylation, methylation, phosphorylation, ubiquitination, and SUMOylation) seems to constitute a code that can be interpreted by other nuclear machinery (March-Diaz, Garcia-Dominguez et al.
2007). The second consists in the ATP-dependent reorganization of interactions between DNA and histones, which provokes the destabilization of the nucleosome structure. The third mechanism of chromatin remodelling lies in the substitution of canonical histones of the octamer by histone variants, which confers new stability and interactions to the nucleosome (Mizuguchi, Shen et al.
2004, Kamakaka and Biggins 2005, March-Diaz, Garcia-Dominguez et al. 2007).