Nucleosomal core histones (H2A, H2B, H3 and H4) must be assembled, replaced or 
exchanged to preserve or modify chromatin organization and function according to 
cellular needs. Histone chaperones escort histones, and play key functions 
during nucleosome assembly/disassembly and in nucleosome structure 
configuration. Because of their location at the periphery of nucleosome, histone 
H2A-H2B dimers are remarkably dynamic. Here we focus on plant histone H2A/H2B 
chaperones, particularly members of the NUCLEOSOME ASSEMBLY PROTEIN-1 (NAP1) and 
FACILITATES CHROMATIN TRANSCRIPTION (FACT) families, discussing their molecular 
features, properties, regulation and function. Covalent histone modifications 
(e.g. ubiquitination, phosphorylation, methylation, acetylation) and H2A 
variants (H2A.Z, H2A.X and H2A.W) are also discussed in view of their crucial 
importance in modulating nucleosome organization and function. We further 
discuss roles of NAP1 and FACT in chromatin-based processes, such as 
transcription, DNA replication and repair. Specific functions of NAP1 and FACT 
are evident when their roles are considered with respect to regulation of plant 
growth and development and in plant responses to environmental stresses. Future 
major challenges remain in order to define in more detail the overlapping and 
specific roles of various members of the NAP1 family as well as differences and 
similarities between NAP1 and FACT family members, and to identify and 
characterize their partners as well as new families of chaperones to understand 
histone variant incorporation and chromatin target specificity.