Plant Actin-Depolymerizing Factors Possess Opposing Biochemical Properties Arising from Key Amino Acid Changes throughout Evolution

Abstract

ORCID IDs: 0000-0002-6213-9791 (D.Q.); 0000-0002-5178-0700 (Y.X.)Functional divergence in paralogs is an important genetic source of evolutionary innovation. Actin-depolymerizing factors (ADFs) are among the most important actin binding proteins and are involved in generating and remodeling actin cytoskeletal architecture via their conserved F-actin severing or depolymerizing activity. In plants, ADFs coevolved with actin, but their biochemical properties are diverse. Unfortunately, the biochemical function of most plant ADFs and the potential mechanisms of their functional divergence remain unclear. Here, in vitro biochemical analyses demonstrated that all 11 ADF genes in Arabidopsis thaliana exhibit opposing biochemical properties. Subclass III ADFs evolved F-actin bundling (B-type) function from conserved F-actin depolymerizing (D-type) function, and subclass I ADFs have enhanced D-type function. By tracking historical mutation sites on ancestral proteins, several fundamental amino acid residues affecting the biochemical functions of these proteins were identified in Arabidopsis and various plants, suggesting that the biochemical divergence of ADFs has been conserved during the evolution of angiosperm plants. Importantly, N-terminal extensions on subclass III ADFs that arose from intron-sliding events are indispensable for the alteration of D-type to B-type function. We conclude that the evolution of these N-terminal extensions and several conserved mutations produced the diverse biochemical functions of plant ADFs from a putative ancestor.

Arabidopsis ACTIN-DEPOLYMERIZING FACTOR3 Is Required for Controlling Aphid Feeding from the Phloem

“…As shown in Figure 2B, GPA population size was comparable on the wild type and the adf3-1 35Spro:ADF4 plants, and significantly lower than that on the adf3-1 mutant, thus confirming the ability of ADF4 overexpression to overcome the adf3-1 defect in limiting GPA infestation. Collectively, the above results in conjunction with the studies of Nan et al (2017) lead us to conclude that the impact of ADF3 on controlling GPA population size is linked to ADF3's function in actin cytoskeleton reorganization.…”

“…Actin Cytoskeleton Destabilizers Restore Resistance to the adf3 Mutant ADF3 is an actin-binding protein that was recently shown to possess F-actin-severing/depolymerizing activity (Nan et al, 2017). F-actin depolymerization assays conducted by us confirm the ability of ADF3 to depolymerize F-actin (Supplemental Fig.…”

“…Both possess actin-severing/depolymerizing activity (HentyRidilla et al, 2014;Nan et al, 2017). However, while ADF3, not ADF4, is essential for defense against the GPA, ADF4, but not ADF3, is required for AvrPphB -triggered immunity against the bacterial pathogen P. syringae (Tian et al, 2009).…”

“…To further test the involvement of ADF3's actindepolymerizing function in controlling GPA infestation, we tested if the adf3-1 defect could be compensated by overexpression of another actin depolymerizing factor, ADF4 Henty-Ridilla et al, 2014;Nan et al, 2017), which exhibits 83% identity and 91% similarity to ADF3 (Supplemental Fig. S4).…”

“…ADF6, which is the lone member of subclass IV, is expressed in all tissues including pollen. Biochemical characterization of Arabidopsis ADFs indicated that all class I, II, and IV ADFs possess F-actin-severing/ depolymerizing activity, with class I ADFs possessing the strongest activities (Nan et al, 2017). In comparison, the class III ADFs lacked F-actin-severing/depolymerizing activity, and instead possessed F-actin bundling activity (Nan et al, 2017).…”