Jung-Sung Chung

Molecular and Physiological Characterization of the Arabidopsis thaliana Oxidation-Related Zinc Finger 2, a Plasma Membrane Protein Involved in ABA and Salt Stress Response Through the ABI2-Mediated Signaling Pathway

CCCH-type zinc finger proteins are important for developmental and environmental responses. However, the precise roles of these proteins in plant stress tolerance are poorly understood. Arabidopsis thaliana Oxidation-related Zinc Finger 2 (AtOZF2) (At4g29190) is an AtOZF1 homolog previously isolated from Arabidopsis, which confers oxidative stress tolerance on plants. The AtOZF2 protein is localized in the plasma membrane, as is AtOZF1. Disruption expression of AtOZF2 led to reduced root length and leaf size. AtOZF2 was implicated to be involved in the ABA and salinity responses. atozf2 antisense lines were more sensitive to ABA and salt stress during the seed germination and cotyledon greening processes. In contrast, AtOZF2-overexpressing plants were more insensitive to ABA and salt stress than the wild type. Interestingly, in the presence of ABA and salt stress, the transcript level of ABA insensitive 2 (ABI2), but not that of ABI1, in AtOZF2-overexpressing plants was lower than that in the wild type, whereas the expression of ABI2 in atozf2 was significantly enhanced. Thus, AtOZF2 is involved in the ABA and salt stress response through the ABI2-mediated signaling pathway. Taken together, these findings provide compelling evidence that AtOZF2 is an important regulator for plant tolerance to abiotic stress.

The CONSTANS-like 4 transcription factor, AtCOL4, positively regulates abiotic stress tolerance through an abscisic acid-dependent manner in Arabidopsis

The precise roles of the B-box zinc finger family of transcription factors in plant stress are poorly understood. Functional analysis was performed on AtCOL4, an Arabidopsis thaliana L. CONSTANS-like 4 protein that is a putative novel transcription factor, and which contains a predicted transcriptional activation domain. Analyses of an AtCOL4 promoter-β-glucuronidase (GUS) construct revealed substantial GUS activity in whole seedlings. The expression of AtCOL4 was strongly induced by abscisic acid (ABA), salt, and osmotic stress. Mutation in atcol4 resulted in increased sensitivity to ABA and salt stress during seed germination and the cotyledon greening process. In contrast, AtCOL4-overexpressing plants were less sensitive to ABA and salt stress compared to the wild type. Interestingly, in the presence of ABA or salt stress, the transcript levels of other ABA biosynthesis and stress-related genes were enhanced induction in AtCOL4-overexpressing and WT plants, rather than in the atcol4 mutant. Thus, AtCOL4 is involved in ABA and salt stress response through the ABA-dependent signaling pathway. Taken together, these findings provide compelling evidence that AtCOL4 is an important regulator for plant tolerance to abiotic stress.

AtSKIP functions as a mediator between cytokinin and light signaling pathway in Arabidopsis thaliana

Key messageAtSKIP participated in cytokinin-regulated leaf initiation. Putative phosphorylated AtSKIP (AtSKIPDD) displayed the opposite function in the leaf development from AtSKIP transgenic seedlings.AbstractAtSKIP, as a multiple protein, is involved in many physiological processes, such as flowering, cell cycle regulator, photomorphogenesis and stress tolerance. However, the mechanism of AtSKIP in these processes is unclear. Here, we identify one gene, AtSKIP, which is associated with cytokinin-regulated leaf growth process in Arabidopsis. The expression of AtSKIP was regulated by cytokinin. Leaf development in AtSKIP overproduced seedlings was independent of light, but promoted by cytokinin, and phosphorylation of AtSKIP (AtSKIPDD) partially interfered with AtSKIP function as a positive regulator in cytokinin signaling, indicative of true leaf formation, and the defects of AtSKIPDD in the true leaf formation could be recovered to some extent by the addition of cytokinin. Moreover, different cytokinin-responsive gene AuthenticResponseRegulator7 (ARR7) promoter-GUS activity further proved that expression of AtSKIP or AtSKIPDD altered endogenous cytokinin signaling in plants. Together, these data indicate that AtSKIP participates in cytokinin-regulated promotion of leaf growth in photomorphogenesis, and that phosphorylation interferes with AtSKIP normal function.

Functional identification of AtSKIP as a regulator of the cell cycle signaling pathway in Arabidopsis thaliana

Light is a key environmental cue controlling plant development, which involves meristemic activation by cell proliferation and differentiation. Here, we identify one gene, AtSKIP, associated with cell cycle-regulated root and leaf growth processes in Arabidopsis. The spatial pattern of β-glucuronidase (GUS) activity indicated that AtSKIP is expressed in the leaf primodia, root meristem region and root vascular system, and can be activated by light. Ectopic expression of AtSKIP resulted in enhanced leaf development but suppressed root elongation in Arabidopsis, whereas AtSKIPDD seedlings displayed retarded leaf growth and normal root growth. Moreover, AtSKIP cells displayed enhanced sensitivity to a cytokinin in a callus induction assay, further demonstrated that AtSKIP expression altered endogenous cell cycle-regulated signaling in plants. Together, these data indicate that AtSKIP participates in cell cycle-mediated growth of leaf and root.

The Arabidopsis thaliana adenosine 5’-phosphosulfate reductase 2 (AtAPR2) participates in flowering time and glucose response

Sugars such as sucrose or glucose function both as building materials for biosynthesis, and as signaling molecules that modulate gene expression. Compared to studies of sugar signaling in bacteria, yeast and animals, knowledge of the signaling pathways in plants is still poorly understood. Here, we investigated the effect of the disruption and overexpression of an Arabidopsis thaliana adenosine 5’-phosphosulfate reductase 2, AtAPR2, on plant responses to glucose stresses. AtAPR2 encodes an enzyme of the sulfate assimilation pathway and it is a member of a three gene family that also includes AtAPR1 and AtAPR3. Expression of AtAPR1, AtAPR2 and AtAPR3 were strongly induced by glucose treatment. Overexpression of AtAPR2 resulted in enhanced cotyledon greening and fresh weight increase when plants were treated with high glucose. By contrast, a T-DNA insertion mutant (atapr2-2) line showed delayed greening and fresh weight growth inhibition in response to glucose and also the non-metabolizable analog 2-deoxyglucose. The expression of three glucose responsive genes, Hexokinase 1 (HXK1), Phenylalanine ammonia lyase 1 (PAL1) and Pathogenesis related gene 5 (PR5), was elevated in AtAPR2-overexpressing and WT plants in response to glucose treatment, but in the atapr2-2 mutant line the transcript level for these genes decreased. Furthermore, AtAPR2-overexpressing plants displayed delayed flowering under long day condition. The data implicates AtAPR2 as a component controlling flowering time and glucose response in Arabidopsis thaliana, although the exact function of AtAPR2 is not clear.

Heterologous expression of the gourd E3 ubiquitin ligase gene LsRZF1 compromises the drought stress tolerance in Arabidopsis thaliana.

Protein ubiquitination is one of the major regulatory processes used by eukaryotic cells. The ubiquitin E3 ligase acts as a main determinant of substrate specificity. However, the precise roles of E3 ligase in plants to drought stress are poorly understood. In this study, a gourd family (Lagenaria siceraria) ortholog of Arabidopsis thaliana RING Zinc Finger 1 (AtRZF1) gene, designated LsRZF1, was identified and characterized. LsRZF1 was reduced by abscisic acid (ABA), osmotic stress, and drought conditions. Compared to wild type, transgenic Arabidopsis plants ectopic expressing LsRZF1 were hypersensitive to ABA and osmotic stress during early seedling development, indicating that LsRZF1 negatively regulates drought-mediated control of early seedling development. Moreover, the ectopic expression of the LsRZF1 gene was very influential in drought sensitive parameters including proline content, water loss, and the expression of dehydration stress-related genes. Furthermore, ubiquitin E3 ligase activity and genetic data indicate that AtRZF1 and LsRZF1 function in similar pathway to control proline metabolism in Arabidopsis under drought condition. Together, these results suggest that the E3 ligase LsRZF1 is an important regulator of water deficit stress during early seedling development.

Reduced Expression of Gongdae Ring Zinc Finger 1 (GdRZF1) Enhances Drought Stress Tolerance in Watermelon (Citrullus lanatus)

Watermelon is a major fruit vegetable around the world. Drought is an abiotic stress factor that affects the productivity and growth of crop plants. To improve the tolerance of watermelon to drought stress, it is important to isolate stress tolerance-related genes. Recently, we characterized the gene for a ubiquitin E3 ligase protein named Lagenaria siceraria RING Zinc Finger 1 (LsRZF1) . In Arabidopsis , LsRZF1 is involved in the drought response through the proline metabolism-mediated pathway. In this study, we identified and characterized a watermelon (Citrullus lanatus cv. Gongdae) homolog of LsRZF1, designated GdRZF1. LsRZF1 antisense (lsrzf1) transgenic watermelon lines showed reduced GdRZF1 expression, and were less sensitive to drought stress than the wild type. Reduced expression of GdRZF1 was also significantly influential in changes in drought-sensitive parameters including relative water content, ion leakage, chlorophyll content, malondialdehyde levels, proline content, and the expression of drought stress-associated genes. Taken together, these findings suggest that GdRZF1 is important for water deficit tolerance in watermelon. OPEN ACCESS Received: