Ji-Hee Min

Overexpression of L-type lectin-like protein kinase 1 confers pathogen resistance and regulates salinity response in Arabidopsis thaliana

Plant receptor-like protein kinases are thought to be involved in various cellular processes mediated by signal transduction pathways. There are about 45 lectin receptor kinases in Arabidopsis, but only a few have been studied. Here, we investigated the effect of the disruption and overexpression of a plasma membrane-localized L-type lectin-like protein kinase 1, AtLPK1 (At4g02410), on plant responses to abiotic and biotic stress. Expression of AtLPK1 was strongly induced by abscisic acid, methyl jasmonate, salicylic acid and stress treatments. Overexpression of AtLPK1 in Arabidopsis resulted in enhanced seed germination and cotyledon greening under high salinity condition, while antisense transgenic lines were more sensitive to salt stress. Activity of three abiotic stress responsive genes, RD29A, RD29B and COR15A, was elevated in AtLPK1-overexpressing plants than that in wild type (WT) plants with salt treatment, whereas the transcript level of these genes in antisense plants decreased compared with WT. Furthermore, AtLPK1-overexpressing plants displayed increased resistance to infection by Botrytis cinerea and exhibited stronger expression of a group of defense-related genes than did WT. The data implicates AtLPK1 plays essential roles at both abiotic and biotic stress response in Arabidopsis thaliana.

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.

The atrzf1 mutation of the novel RING-type E3 ubiquitin ligase increases proline contents and enhances drought tolerance in Arabidopsis

The covalent attachment of ubiquitin to proteins plays a fundamental role in the regulation of cellular function through biological events involving abiotic or biotic stress responses, immune responses, and apoptosis. Here, we characterize the biological function of the Arabidopsis thaliana RING Zinc Finger 1 (AtRZF1) in dehydration response. AtRZF1 was significantly reduced by drought stress. The atrzf1 mutant was less sensitive to osmotic stress than the wild-type during early seedling development, whereas transgenic plants overexpressing AtRZF1 were hypersensitive, indicating that AtRZF1 negatively regulates drought-mediated control of early seedling development. Moreover, the ectopic expression of the AtRZF1 gene was very significantly influential in drought sensitive parameters including proline content, water loss, membrane ion leakage and the expression of dehydration stress-related genes. AtRZF1 is a functional E3 ubiquitin ligase, and its conserved C3H2C3-type RING domain is likely important for the biological function of AtRZF1 in drought response. Together, these results suggest that the E3 ligase AtRZF1 is an important regulator of water deficit stress during early seedling development.

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.

PCA22 acts as a suppressor of atrzf1 to mediate proline accumulation in response to abiotic stress in Arabidopsis

Highlight PCA22 negatively regulates the drought response through the modulation of osmolytic components and regulates pollen tube length in Arabidopsis.

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.

Arabidopsis Basic Helix-Loop-Helix 34 (bHLH34) Is Involved in Glucose Signaling through Binding to a GAGA Cis-Element

The modulation of glucose (Glc) homeostasis and signaling is crucial for plant growth and development. Nevertheless, the molecular signaling mechanism by which a plant senses a cellular Glc level and coordinates the expression of Glc-responsive genes is still incompletely understood. Previous studies have shown that Arabidopsis thaliana plasma membrane Glc-responsive regulator (AtPGR) is a component of the Glc-responsive pathway. Here, we demonstrated that a transcription factor bHLH34 binds to 5′-GAGA-3′ element of the promoter region of AtPGR in vitro, and activates beta-glucuronidase (GUS) activity upon Glc treatment in AtPGR promoter-GUS transgenic plants. Gain- and loss-of-function analyses suggested that the bHLH34 involved in the responses to not only Glc, but also abscisic acid (ABA) and salinity. These results suggest that bHLH34 functions as a transcription factor in the Glc-mediated stress responsive pathway as well as an activator of AtPGR transcription. Furthermore, genetic experiments revealed that in Glc response, the functions of bHLH34 are different from that of a bHLH104, a homolog of bHLH34. Collectively, our findings indicate that bHLH34 is a positive regulator of Glc, and may affect ABA or salinity response, whereas bHLH104 is a negative regulator and epistatic to bHLH34 in the Glc response.

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: