Arabidopsis thaliana subclass I ACTIN DEPOLYMERIZING FACTORs and vegetative ACTIN2/8 are novel regulators of endoreplication.

Endoreplication is a type of cell cycle where genome replication occurs without mitosis. An increase of ploidy level by endoreplication is often associated with cell enlargement and an enhanced plant growth. Here we report Arabidopsis thaliana subclass I ACTIN DEPOLYMERIZING FACTORs (ADFs) and vegetative ACTIN2/8 as novel regulators of endoreplication. A. thaliana has 11 ADF members that are divided into 4 subclasses. Subclass I consists of four members, ADF1, -2, -3, and -4, all of which constitutively express in various tissues. We found that both adf4 knockout mutant and transgenic plants in which expressions of all of four subclass I ADFs are suppressed (ADF1-4Ri) showed an increased leaf area of mature first leaves, which was associated with a significant increase of epidermal pavement cell area. Ploidy analysis revealed that the ploidy level was significantly increased in mature leaves of ADF1-4Ri. The increased ploidy was also observed in roots of adf4 and ADF1-4Ri, as well as in dark-grown hypocotyls of adf4. Furthermore, double mutants of vegetative ACT2 and ACT8 (act2/8) exhibited an increase of leaf area and ploidy level in mature leaves. Therefore, actin-relating pathway could regulate endoreplication. The possible mechanisms that actin and ADFs regulate endoreplication are discussed.