FZR2/CCS52A1 mediated endoreduplication in Arabidopsis development

Plant organogenesis generally involves three basic processes: cell division, cell expansion and cell differentiation. Endoreduplication, a process of genome replication without intervening mitosis, often occurs during cell expansion and cell differentiation. The switch from the mitotic cell cycle to the endocycle, however, is still poorly understood in plants. We have recently demonstrated that FIZZY-RELATED2 (FZR2) is a factor controlling endoreduplication in Arabidopsis. fzr2 mutants lacked gross morphological defects but showed a general decrease of endoploidy level in trichomes and other leaf cells, while expression of FZR2 under constitutive or tissue specific promoters induced extra or ectopic endoreduplication in all tissues examined. We also showed that decrease of leaf cell size in fzr2 mutants could be compensated by increased cell proliferation. In this addendum, we discuss additional phenotypes of FZR2 misexpression, including apparent mosaic leaf sectors in which local cell overexpansion due to 35S::FZR2 appears to be compensated by reduced cell expansion in neighboring tissues.