TOPOISOMERASE 6B is involved in chromatin remodelling associated with control of carbon partitioning into secondary metabolites and cell walls, and epidermal morphogenesis in Arabidopsis

Plant growth is continuous and modular, a combination that allows morphogenesis by cell division and elongation and serves to facilitate adaptation to changing environments. We previously characterized the pleiotropic phenotypes of the harlequin/hlq mutant, isolated on the basis of ectopic expression of ABA- and auxin-inducible proDc3:GUS. Mutants are skotomorphogenic, have deformed and collapsed epidermal cells which accumulate callose and starch, cell walls abundant in pectins and cell wall proteins, and abnormal and reduced root hairs and leaf trichomes. We have isolated hlq, and show that it is an allele of bin3/hyp6/rhl3/Topoisomerase6B. Mutants and inhibitors affecting the cell wall phenocopy several of the traits displayed in hlq. We performed a microarray analysis and observed coordinated expression of physically adjacent pairs/sets of genes in hlq, suggesting a direct effect on chromatin. We also identified histones, WRKY and IAA/AUX transcription factors, aquaporins, a