<i>Arabidopsis thaliana ACTIN DEPOLYMERIZING FACTOR</i> s play a role in leaf senescence regulation

ACTIN DEPOLYMERIZING FACTORs (ADFs) regulate the organization and dynamics of actin microfilaments (AFs) by cleavage and depolymerization of AFs. The Arabidopsis thaliana genome encodes 11 ADF genes grouped into 4 subclasses. Subclass I ADFs, ADF1, -2, -3, and -4, are expressed in all vegetative tissues and are reportedly involved in the regulation of plant growth, and abiotic and biotic stress responses. Furthermore, the nuclear localization of ADF4 is seemingly important in disease response. Here, we present data that indicate a previously unknown regulatory role of subclass I ADFs in the regulation of leaf senescence. ADF4 knockout mutants (adf4) and transgenic lines in which the expression of all members of subclass I ADFs was downregulated (ADF1-4Ri) showed acceleration of both dark-induced and age-dependent leaf senescence. Upregulation of the expression of senescence-associated genes, such as SAG13, SGR1, PPH, and WRKY53, occurred earlier in adf4 and ADF1-4Ri lines than in wild type. Examination of the expression of subclass I ADFs genes during age-dependent leaf senescence revealed a reduced expression of ADF4 but not expressions of other subclass I members. Additionally, we showed that nuclear localization of ADF4 was important for regulating leaf senescence. Altogether, our data indicate that subclass I ADFs, particularly ADF4, play an important role in the regulation of leaf senescence.