ACTIN2 Functions in Chloroplast Photorelocation Movement in Arabidopsis thaliana

Abstract

Chloroplast movement is regulated by dynamic reorganization of the actin cytoskeleton. To gain insight into the function of ACT2 in chloroplast movement, we examined the effect of the act2-3 mutation, in which a T-DNA is inserted at the second exon of the ACT2 gene, and investigated a transgenic Arabidopsis plant expressing the GFP-ACT2 fusion protein. Chloroplast movement in the act2-3 mutant was retarded, especially during the avoidance response, compared with that in the WT. We further verified the physiological response of transgenic Arabidopsis expressing the GFP-ACT2 fusion gene with a 6xGSS linker sequence, which was recently reported to enable the direct visualization of actin filaments in a transient expression system. Although the expression of GFP-ACT2 had highly detrimental effects on the growth and development of transgenic Arabidopsis plants, GFP-ACT2 was incorporated into chloroplast actin (cp-actin) filaments instead of cortical actin filaments. The analyses of the act2 mutant and GFP-ACT2 transgenic plants suggest that ACT2 functions in chloroplast movement as a component of cp-actin filaments and that cp-actin filaments are differently regulated compared to cortical actin filaments.