Interactions between Auxin Transport and the Actin Cytoskeleton in Developmental Polarity ofFucus distichusEmbryos in Response to Light and Gravity

Abstract

Land plants orient their growth relative to light and gravity through complex mechanisms that require auxin redistribution. Embryos of brown algae use similar environmental stimuli to orient their developmental polarity. These studies of the brown algae Fucus distichus examined whether auxin and auxin transport are also required during polarization in early embryos and to orient growth in already developed tissues. These embryos polarize with the gravity vector in the absence of a light cue. The auxin, indole-3-acetic acid (IAA), and auxin efflux inhibitors, such as naphthylphthalamic acid (NPA), reduced environmental polarization in response to gravity and light vectors. Young rhizoids are negatively phototropic, and NPA also inhibits rhizoid phototropism. The effect of IAA and NPA on gravity and photopolarization is maximal within 2.5 to 4.5 h after fertilization (AF). Over the first 6 h AF, auxin transport is relatively constant, suggesting that developmentally controlled sensitivity to auxin determines the narrow window during which NPA and IAA reduce environmental polarization. Actin patches were formed during the first hour AF and began to photolocalize within 3 h, coinciding with the time of NPA and IAA action. Treatment with NPA reduced the polar localization of actin patches but not patch formation. Latrunculin B prevented environmental polarization in a time frame that overlaps the formation of actin patches and IAA and NPA action. Latrunculin B also altered auxin transport. Together, these results indicate a role for auxin in the orientation of developmental polarity and suggest interactions between the actin cytoskeleton and auxin transport in F. distichus embryos.

Rice actin-binding protein RMD is a key link in the auxin–actin regulatory loop that controls cell growth

“…Genetic or pharmacological manipulation of PAT that disturbs the auxin maximum dramatically alters root patterning (1,31). Numerous pharmacological investigations have confirmed the close correlation between PAT and the actin cytoskeleton (11,(16)(17)(18). In Arabidopsis, auxin transport inhibitors like 2,3,5-triiodobenzoic acid induce bundling of actin filaments and inhibit endocytosis (15,18).…”

“…For example, the auxin IAA induces actin bundling in Arabidopsis thaliana root cells (15). Pharmacological studies suggest that the actin cytoskeleton partially affects the directional transport of auxin by modulating cycling of auxin efflux carriers (16,17). In Arabidopsis root cells, the actin inhibitor cytochalasin D inhibits brefeldin A (BFA)-mediated PIN1 internalization (11), whereas latrunculin B impairs the polar localization of PIN1 in protophloem cells (18).…”

Brassinosteroids Stimulate Plant Tropisms through Modulation of Polar Auxin Transport in Brassica and Arabidopsis

“…Recent studies revealed the important roles of the actin cytoskeleton in auxin transport and related growth (Geldner et al, 2001;Friml et al, 2002). Treatment with latrunculin B, an inhibitor of actin filament assembly, may enhance gravitropism through the alteration of auxin transport Sun et al, 2004). The formation of cortical F-actin in Arabidopsis seedlings in turn is controlled by ROP (for Rho-of-plant) GTPases , and actin-depolymerizing factor mediates RAC/ROP GTPase-regulated pollen tube growth (Chen et al, 2003).…”

Auxin Metabolism and Function in the Multicellular Brown AlgaEctocarpus siliculosus

“…Given its large size and its ease of manipulation, the Fucales zygote has been particularly amenable to cytological and pharmacological experiments (Kropf, 1997). Polarization of the zygote after fertilization involves several subcellular components (cell wall, microtubules, centrioles, and actin; for review, see Kropf, 1992) and is affected by auxin, which alters the polarity of the embryo and its developmental pattern (Basu et al, 2002;Sun et al, 2004). However, Fucus is not amenable to genetic studies, limiting its utility in further investigations of the processes controlling morphogenesis in brown algae.…”