High expression of Lifeact in Arabidopsis thaliana reduces dynamic reorganization of actin filaments but does not affect plant development.

ABSTRACT

Lifeact is a novel probe that labels actin filaments in a wide range of organisms. We compared the localization and reorganization of LifeactVenus-labeled actin filaments in Arabidopsis root hairs and root epidermal cells of lines that express different levels of Lifeact Venus with that of actin filaments labeled with GFPFABD2, a commonly used probe in plants. Unlike GFPFABD2, LifeactVenus labeled the highly dynamic fine F-actin in the subapical region of tip-growing root hairs. LifeactVenus expression at varying levels was not observed to affect plant development. However, at expression levels comparable to those of GFPFABD2 in a well-characterized marker line, LifeactVenus reduced reorganization rates of bundles of actin filaments in root epidermal cells. Reorganization rates of cytoplasmic strands, which reflect the reorganization of the actin cytoskeleton, were also reduced in these lines. Moreover, in the same line, LifeactVenus-decorated actin filaments were more resistant to depolymerization by latrunculin B than those in an equivalent GFPFABD2-expressing line. In lines where Lifeact Venus is expressed at lower levels, these effects are less prominent or even absent. We conclude that Lifeact Venus reduces remodeling of the actin cytoskeleton in Arabidopsis in a concentration-dependent manner. Since this reduction occurs at expression levels that do not cause defects in plant development, selection of normally growing plants is not sufficient to determine optimal Lifeact expression levels. When correct expression levels of Lifeact have been determined, it is a valuable probe that labels dynamic populations of actin filaments such as fine F-actin, better than FABD2 does.