Hydrogen Sulfide Disturbs Actin Polymerization via <i>S</i>-Sulfhydration Resulting in Stunted Root Hair Growth

Abstract

Hydrogen sulfide (H₂S) is an important signaling molecule in plants. Our previous report suggested that H₂S signaling affects the actin cytoskeleton and root hair growth. However, the underlying mechanisms of its effects are not understood. <i>S</i>-Sulfhydration of proteins is regulated directly by H₂S, which converts the thiol groups of cysteine (Cys) residues to persulfides and alters protein function. In this work, we studied the effects of <i>S</i>-sulfhydration on actin dynamics in Arabidopsis (<i>Arabidopsis thaliana</i>). We generated transgenic plants overexpressing the H₂S biosynthesis-related genes <i>l-CYSTEINE DESULFHYDRASE</i> (<i>LCD</i>) and <i>d-CYSTEINE DESULFHYDRASE</i> in the <i>O-acetylserine(thiol)lyase isoform a1</i> (<i>oasa1</i>) mutant and Columbia-0 backgrounds. The H₂S content increased significantly in overexpressing <i>LCD</i>/<i>oasa1</i> plants. The density of filamentous actin (F-actin) bundles and the F-actin/globular actin ratio decreased in overexpressing <i>LCD</i>/<i>oasa1</i> plants. <i>S</i>-Sulfhydration also was enhanced in overexpressing <i>LCD</i>/<i>oasa1</i> plants. An analysis of actin dynamics suggested that <i>S</i>-sulfhydration inhibited actin polymerization. We also found that ACTIN2 (ACT2) was <i>S</i>-sulfhydrated at Cys-287. Cys-287 is adjacent to the D-loop, which acts as a central region for hydrophobic and electrostatic interactions and stabilizes F-actin filaments. Overaccumulation of H₂S caused the depolymerization of F-actin bundles and inhibited root hair growth. Introduction of <i>ACT2</i> carrying a Cys-287-to-Ser mutation into an <i>act2-1</i> mutant partially suppressed H₂S-dependent inhibition of root hair growth. We conclude that H₂S regulates actin dynamics and affects root hair growth.