Structure and Evolution of the Actin Gene Family in Arabidopsis thaliana

Abstract

Higher plants contain families of actin-encoding genes that are divergent and differentially expressed. Progress in understanding the functions and evolution of plant actins has been hindered by the large size of the actin gene families. In this study, we characterized the structure and evolution of the actin gene family in Arabidopsis thaliana. DNA blot analyses with gene-specific probes suggested that all 10 of the Arabidopsis actin gene family members have been isolated and established that Arabidopsis has a much simpler actin gene family than other plants that have been examined. Phylogenetic analyses suggested that the Arabidopsis gene family contains at least two ancient classes of genes that diverged early in land plant evolution and may have separated vegetative from reproductive actins. Subsequent divergence produced a total of six distinct subclasses of actin, and five showed a distinct pattern of tissue specific expression. The concordance of expression patterns with the phylogenetic structure is discussed. These subclasses appear to be evolving independently, as no evidence of gene conversion was found. The Arabidopsis actin proteins have an unusually large number of nonconservative amino acid substitutions, which mapped to the surface of the actin molecule, and should effect protein-protein interactions.

Microtubule Dynamics Plays a Vital Role in Plant Adaptation and Tolerance to Salt Stress

“…Actin cytoskeletons are composed of two classes, which are vegetative (ACT2, ACT7, and ACT8) and reproductive (ACT1, ACT3, ACT4, ACT11, and ACT12). ACT7 transcription is high in vegetative organs and induced by auxin [ 51 ]. The act11 mutant decreases pollen germination and increases pollen tube growth by increasing the actin turnover rate [ 52 ].…”

Cytoskeleton and plant organogenesis

“…Two possible explanations, which are not mutually exclusive, have been proposed for the observation that groups of highly similar cytoskeleton-related genes with partially overlapping expression pattern have been maintained in plants during evolution. First, multiple genes with similar coding sequences but different expression signals may allow enhanced flexibility in expression in response to developmental cues and environmental signals (McDowell et al 1996). Second, it is conceivable that coexpression of non-identical but highly similar proteins can increase the functionality, the responsiveness and the stability of a system, a concept that has been termed 'isovariant dynamics' (Meagher et al 1999a).…”

Actin Isovariant ACT7 Modulates Root Thermomorphogenesis by Altering Intracellular Auxin Homeostasis

“…Although ACT7 and ACT8 have high homology (7% difference at amino acid level), here we demonstrate that root thermomorphogenesis is linked to ACT7 but not ACT8 . This is possibly due to the subclass variance, and subtle changes in biochemical properties between ACT7 and ACT8 [ 59 ]. Arabidopsis vegetative actin subclass II is in a sister group of the subclass I clade in the phylogenetic tree.…”

“…Subclass I differs by 7% amino acid from subclass II, and these classes of Arabidopsis actin are more closely related to the genes from other plant species than they are to each other. ACT2/8 clade is closer to actin genes from maize and rice compared to ACT7 , while ACT7 is more similar to the genes from pea, carrot, potato, and pine than ACT8 , suggesting that they originated from different lineages [ 59 ]. The differences between these two subclasses are also evident in their amino acid compositions.…”

“…His41 and ser170 of subclass I are also replaced with Thr41 and Ala170 in subclass II. These subtle changes in amino acid compositions have the potential to alter actin–actin or actin–actin binding protein interactions [ 59 ]. Differential biochemical properties of ACT2 and ACT7 had already been reported in terms of polymerization and phosphate release rates.…”