PLANT CHROMATIN STRUCTURE AND POSTTRANSLATIONAL MODIFICATIONS

Although a majority of the key works on chromatin structure and functi on have been carried out using animal tissues, studies of plant chroma tin and the characterization of the histones and nonhistone chromosoma l proteins are now developing well. There are clear functional differe nces between plant and animal genomes, including the percentage of tot al DNA transcribed, levels of ploidy, and the pathways of morphogenesi s and cell differentiation. It is therefore not surprising that differ ences are appearing between animal and plant chromatin, for example, t he consensus amino acid sequence for the plant H3 globular domain; the extensions to the basic domain regions of some plant histones such as H2A, which have specific interactions with Linker DNA; the larger mol ecular weight of the plant H1 molecule with its extended basic domains correlated with short lengths of linker DNA, and the absence of the f ive residue binding segment in the globular part of plant H1, which su ggests differences in the organization of higher order structure in pl ant chromatin. There are also unifying features between plant and anim al chromatin, and the nature of plant material makes its study particu larly advantageous in several areas. The regular nucleosome repeat and short lengths of linker DNA in some plants should provide more regula r order structures for study, in which in the near absence of linker D NA, nucleosome position is the main, if not sole, determining factor i n model building. However, the improved characterization and isolation of plant chromatin and associated molecules, for example, the isolati on of the SPKK kinase gene in pea, are essential if major progress is to be made in our understanding of functional activities.