Arabidopsis thaliana ACTIN DEPOLYMERIZING FACTORs play a role in leaf senescence regulation

Abstract

ABSTRACTACTIN DEPOLYMERIZING FACTORs (ADFs) regulate the organization and dynamics of actin microfilaments (AFs) by cleavage and depolymerization of AFs. TheArabidopsis thalianagenome encodes 11ADFgenes grouped into four subclasses. Subclass IADFs,ADF1,-2,-3, and-4, are expressed in all vegetative tissues and are reportedly involved in the regulation of plant growth, and biotic and abiotic stress responses. Furthermore, the nuclear localization of ADF4 is seemingly important in disease responses. Here, we present data that indicate a previously unknown regulatory role of subclass I ADFs in leaf senescence.ADF4knockout mutants (adf4) and transgenic lines in which the expression of all members of subclass IADFs was downregulated (ADF1-4Ri) showed acceleration of both dark-induced and age-dependent leaf senescence. Among the eightACTINgenes encoded inA. thaliana,ACT2,-7, and-8are expressed in vegetative tissues. In contrast toadf4andADF1-4Ri, neitherACT2andACT8double mutant (act2/8), norACT7knockout mutant (act7), showed accelerated leaf senescence. Upregulation of the expression of senescence-associated genes occurred earlier inadf4andADF1-4Rilines than in wild type. Examination of the expression of subclass IADFs genes during senescence revealed a reduced expression ofADF4but not 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.