A Single Vegetative Actin Isovariant Overexpressed under the Control of Multiple Regulatory Sequences Is Sufficient for NormalArabidopsisDevelopment

Abstract

The relative significance of gene regulation and protein isovariant differences remains unexplored for most gene families, particularly those participating in multicellular development. Arabidopsis thaliana encodes three vegetative actins, ACT2, ACT7, and ACT8, in two ancient and highly divergent subclasses. Mutations in any of these differentially expressed actins revealed only mild phenotypes. However, double mutants were extremely dwarfed, with altered cell and organ morphology and an aberrant F-actin cytoskeleton (e.g., act2-1 act7-4 and act8-2 act7-4) or totally root-hairless (e.g., act2-1 act8-2). Our studies suggest that the three vegetative actin genes and protein isovariants play distinct subclass-specific roles during plant morphogenesis. For example, during root development, ACT7 was involved in root growth, epidermal cell specification, cell division, and root architecture, and ACT2 and ACT8 were essential for root hair tip growth. Also, genetic complementation revealed that the ACT2 and ACT8 isovariants, but not ACT7, fully rescued the root hair growth defects of single and double mutants. Moreover, we synthesized fully normal plants overexpressing the ACT8 isovariant from multiple actin regulatory sequences as the only vegetative actin in the act2-1 act7-4 background. In summary, it is evident that differences in vegetative actin gene regulation and the diversity in actin isovariant sequences are essential for normal plant development.

ArabidopsisVILLIN1 and VILLIN3 Have Overlapping and Distinct Activities in Actin Bundle Formation and Turnover

“…Biochemical and in planta functional differences have been demonstrated previously for isovariants of actin and the actin binding proteins, profilin and ADF (Kandasamy et al, 2002(Kandasamy et al, , 2007(Kandasamy et al, , 2009Staiger and Blanchoin, 2006). There is also genetic evidence for isovariants exhibiting similar and interchangeable functions, like the vegetative actins and the SCAR isovariants (Zhang et al, 2008;Kandasamy et al, 2009). The villins may therefore have redundant functions, work synergistically, or have unique properties altogether.…”

Class XI Myosins Are Required for Development, Cell Expansion, and F-Actin Organization in Arabidopsis

“…An unexpected role of myosins in the exclusion of F-actin bundles from the apical zone of root hairs (Figure 8) requires a distinct interpretation. It is known that the transition from root hair bulge to polarized growth involves apical F-actin rearrangement (Kandasamy et al, 2009;Szymanski and Cosgrove, 2009). A similar process governed by F-actin remodeling proteins operates during the polarized growth of moss cells (Vidali et al, 2009).…”

BENT UPPERMOST INTERNODE1Encodes the Class II Formin FH5 Crucial for Actin Organization and Rice Development

“…Simultaneous downregulation of ACTIN2 and ACTIN7 reduced cell elongation in Arabidopsis hypocotyls (Kandasamy et al, 2009). Misexpression of actin regulatory proteins, such as profilin and actin-depolymerizing factors, also perturbs cell elongation (Ramachandran et al, 2000;Dong et al, 2001;Kandasamy et al, 2009).…”

“…Simultaneous downregulation of ACTIN2 and ACTIN7 reduced cell elongation in Arabidopsis hypocotyls (Kandasamy et al, 2009). Misexpression of actin regulatory proteins, such as profilin and actin-depolymerizing factors, also perturbs cell elongation (Ramachandran et al, 2000;Dong et al, 2001;Kandasamy et al, 2009). In addition, the actin cytoskeleton plays pivotal roles in polar cell expansion and the establishment of cell division planes by governing cytoplasmic streaming, organelle movement, and vesicle transport (Martin et al, 2001;Staiger and Blanchoin, 2006).…”