Jisheng Li

Hydrogen sulfide modulates actin-dependent auxin transport via regulating ABPs results in changing of root development in Arabidopsis.

Hydrogen sulfide (H2S) signaling has been considered a key regulator of plant developmental processes and defenses. In this study, we demonstrate that high levels of H2S inhibit auxin transport and lead to alterations in root system development. H2S inhibits auxin transport by altering the polar subcellular distribution of PIN proteins. The vesicle trafficking and distribution of the PIN proteins are an actin-dependent process. H2S changes the expression of several actin-binding proteins (ABPs) and decreases the occupancy percentage of F-actin bundles in the Arabidopsis roots. We observed the effects of H2S on F-actin in T-DNA insertion mutants of cpa, cpb and prf3, indicating that the effects of H2S on F-actin are partially removed in the mutant plants. Thus, these data imply that the ABPs act as downstream effectors of the H2S signal and thereby regulate the assembly and depolymerization of F-actin in root cells. Taken together, our data suggest that the existence of a tightly regulated intertwined signaling network between auxin, H2S and actin that controls root system development. In the proposed process, H2S plays an important role in modulating auxin transport by an actin-dependent method, which results in alterations in root development in Arabidopsis.

Arabidopsis CROLIN1, a novel plant actin-binding protein, functions in cross-linking and stabilizing actin filaments.

Background: Higher order actin filament structures are involved in many cellular processes. Results: Arabidopsis CROLIN1 contains a predicted actin-cross-linking domain and shows F-actin binding, cross-linking, and stabilizing activities in vitro. Conclusion: CROLIN1 functions as an actin-binding and cross-linking protein. Significance: CROLIN1 is a previously undiscovered plant actin-cross-linking protein. Higher order actin filament structures are necessary for cytoplasmic streaming, organelle movement, and other physiological processes. However, the mechanism by which the higher order cytoskeleton is formed in plants remains unknown. In this study, we identified a novel actin-cross-linking protein family (named CROLIN) that is well conserved only in the plant kingdom. There are six isovariants of CROLIN in the Arabidopsis genome, with CROLIN1 specifically expressed in pollen. In vitro biochemical analyses showed that CROLIN1 is a novel actin-cross-linking protein with binding and stabilizing activities. Remarkably, CROLIN1 can cross-link actin bundles into actin networks. CROLIN1 loss of function induces pollen germination and pollen tube growth hypersensitive to latrunculin B. All of these results demonstrate that CROLIN1 may play an important role in stabilizing and remodeling actin filaments by binding to and cross-linking actin filaments.

Nitric oxide increases mitochondrial respiration in a cGMP-dependent manner in the callus from Arabidopsis thaliana.

Nitric oxide (NO) acts as a key molecule in many physiological processes in plants. In this study, the roles of NO in mitochondrial respiration were investigated in the calli from wild-type Arabidopsis and NO associated 1 mutant (Atnoa1) which has a reduced endogenous NO level. Long-term exposure of wild-type Arabidopsis callus to sodium nitroprusside (SNP) increased mitochondrial respiration in both cytochrome and alternative pathways. In Atnoa1 callus, the capacity of both the cytochrome pathway and the alternative pathway was lower than that in wild-type callus. Further study indicated that NO enhanced the transcript abundance of genes encoding mitochondrial respiration-chain proteins as well as the protein expression of the NADH-ubiquinone reductase 75 kDa subunit and the alternative oxidase 1/2 in wild-type and Atnoa1 calli. 2-Phenyl-4,4,5,5-tetremethy-limidazolinone-1-oxyl-3-oxide (PTIO), a NO scavenger, inhibited the effects of NO in both calli. Co-incubation of callus with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor, also abolished NO effects. The membrane-permeable cGMP analog 8Br-cGMP mimicked NO effects. Moreover, the alternative pathway showed a higher sensitivity to the cellular cGMP changes than the cytochrome pathway did in gene transcription, protein expression and O(2) consumption. Taken together, NO could enhance mitochondrial respiration in both cytochrome and alternative pathways in a cGMP-dependent manner in Arabidopsis.

Hydrogen sulfide - cysteine cycle system enhances cadmium tolerance through alleviating cadmium-induced oxidative stress and ion toxicity in Arabidopsis roots

Cadmium (Cd2+) is a common toxic heavy metal ion. We investigated the roles of hydrogen sulfide (H2S) and cysteine (Cys) in plant responses to Cd2+ stress. The expression of H2S synthetic genes LCD and DES1 were induced by Cd2+ within 3 h, and endogenous H2S was then rapidly released. H2S promoted the expression of Cys synthesis-related genes SAT1 and OASA1, which led to endogenous Cys accumulation. The H2S and Cys cycle system was stimulated by Cd2+ stress, and it maintained high levels in plant cells. H2S inhibited the ROS burst by inducing alternative respiration capacity (AP) and antioxidase activity. H2S weakened Cd2+ toxicity by inducing the metallothionein (MTs) genes expression. Cys promoted GSH accumulation and inhibited the ROS burst, and GSH induced the expression of phytochelatin (PCs) genes, counteracting Cd2+ toxicity. In summary, the H2S and Cys cycle system played a key role in plant responses to Cd2+ stress. The Cd2+ tolerance was weakened when the cycle system was blocked in lcddes1-1 and oasa1 mutants. This paper is the first to describe the role of the H2S and Cys cycle system in Cd2+ stress and to explore the relevant and specificity mechanisms of H2S and Cys in mediating Cd2+ stress.

cGMP and ethylene are involved in maintaining ion homeostasis under salt stress in Arabidopsis roots

AbstractKey messagecGMP promotes ethylene production and enhances the perception of ethylene. Endogenous ethylene or cGMP accumulation maintains ion homeostasis to enhancing salt resistance.etr1-3is insensitive to cGMP under salt stress.Abstract In the present study, we presented a signaling network involving ethylene and cGMP in salt resistance pathway of Arabidopsis roots. Results showed that the ethylene-insensitive mutant etr1-3 was more sensitive to salt stress than the wild type (WT). etr1-3 displayed a greater electrolyte leakage, thiobarbituric acid reactive substances and Na+/K+ ratio, but a lower plasma membrane (PM) H+-ATPase activity compared to WT under the different NaCl contents. Application of 1-aminocyclopropane-1-carboxylic acid (ACC, an ethylene precursor) or 8-Br-cGMP (the cGMP analog) alleviated NaCl-induced injury by maintaining a lower Na+/K+ ratio and increasing PM H+-ATPase activity in WT, but not in etr1-3. Roots treated with 8-Br-cGMP could promote ethylene production and enhance the expression of ACC synthase gene in WT. In addition, the 8-Br-cGMP action in NaCl stress was inhibited by aminooxyacetic acid (an inhibitor of ethylene biosynthesis), but 6-Anilino-5,8-quinolinedione (Ly83583, a guanylate cyclase inhibitor) could not affect ACC action in WT. These results suggest that ethylene functions as a downstream signal of cGMP that stimulates the PM H+-ATPase activity, which finally results in regulating ion homeostasis in Arabidopsis tolerance to salt. Moreover, cGMP enhanced the perception of ethylene in Arabidopsis under salt stress, which reversed the salt-induced increase of ETR1 and increased ERF1 at the transcript levels in WT. In a word, cGMP modulates salt resistance pathway of ethylene through regulating biosynthesis and perception of ethylene in Arabidopsis roots.

Ethylene promotes pollen tube growth by affecting actin filament organization via the cGMP-dependent pathway in Arabidopsis thaliana

Ethylene and cGMP are key regulators of plant developmental processes. In this study, we demonstrate that ethylene or cGMP promote pollen tube growth in a dose-dependent manner. The etr1–1 mutant was found to be insensitive to ethylene with regard to pollen tube growth, while the growth-promoting effect of ethylene in etr2–2, ein4–4, or ein4–7 did not change, suggesting that ethylene signaling was mainly perceived by ETR1. However, the function of cGMP was not inhibited in etr1–1 and pollen tubes became insensitive to ethylene when the endogenous cGMP level was artificially decreased. This shows that cGMP is necessary for the control of pollen tube growth and that it might be a downstream component of ETR1 in the ethylene signaling pathway. Our study also found that ethylene or cGMP increase the actin bundles and elevated the percentage of relative amount of F-actin, while removal of cGMP decreased actin bundles abundance and altered the ratio of F-actin in the tip and base regions of pollen tubes. In conclusion, our data suggests that ethylene functions as the upstream signal of cGMP, and that both signals promote pollen germination and tube growth by regulating F-actin, which is essential for vesicular transport and cytoplasmic streaming.

Hydrogen Sulfide Disturbs Actin Polymerization via S-Sulfhydration Resulting in Stunted Root Hair Growth

Hydrogen sulfide-induced S-sulfhydration affects actin dynamics and root hair growth in Arabidopsis. 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. S-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 S-sulfhydration on actin dynamics in Arabidopsis (Arabidopsis thaliana). We generated transgenic plants overexpressing the H2S biosynthesis-related genes l-CYSTEINE DESULFHYDRASE (LCD) and d-CYSTEINE DESULFHYDRASE in the O-acetylserine(thiol)lyase isoform a1 (oasa1) mutant and Columbia-0 backgrounds. The H2S content increased significantly in overexpressing LCD/oasa1 plants. The density of filamentous actin (F-actin) bundles and the F-actin/globular actin ratio decreased in overexpressing LCD/oasa1 plants. S-Sulfhydration also was enhanced in overexpressing LCD/oasa1 plants. An analysis of actin dynamics suggested that S-sulfhydration inhibited actin polymerization. We also found that ACTIN2 (ACT2) was S-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 ACT2 carrying a Cys-287-to-Ser mutation into an act2-1 mutant partially suppressed H2S-dependent inhibition of root hair growth. We conclude that H2S regulates actin dynamics and affects root hair growth.

Ethylene-induced hydrogen sulfide negatively regulates ethylene biosynthesis by persulfidation of ACO in tomato under osmotic stress

A number of recent studies identified hydrogen sulfide (H2S) as an important signal in plant development and adaptation to environmental stress. H2S has been proven to participate in ethylene-induced stomatal closure, but how the signaling pathways of H2S and ethylene interact is still unclear. Here, we reveal how H2S controls the feedback-regulation of ethylene biosynthesis in tomato (Solanum lycopersicum) under osmotic stress. We found that ethylene induced the production of H2S in guard cells. The supply of hypotaurine (HT; a H2S scavenger) or DL-pro-pargylglycine (PAG; a synthetic inhibitor of H2S) removed the effect of ethylene or osmotic stress on stomatal closure. This suggests that ethylene-induced H2S is a downstream component of osmotic stress signaling, which is required for ethylene-induced stomatal closure under osmotic stress. We further found that H2S inhibited ethylene synthesis through inhibiting the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidases (ACOs) by persulfidation. A modified biotin-switch method (MBST) showed that H2S can induce persulfidation of LeACO1 and LeACO2 in a dose-dependent manner, and that persulfidation inhibits the activity of LeACO1 and LeACO2. We also found that LeACO1 is persulfidated at cysteine 60. These data suggested that ethylene-induced H2S negatively regulates ethylene biosynthesis by persulfidation of LeACOs. In addition, H2S was also found to inhibit the expression of LeACO genes. The results provide insight on the general mode of action of H2S and contribute to a better understanding of a plant’s response to osmotic stress.