HOS1, a genetic locus involved in cold-responsive gene expression in arabidopsis.

Low-temperature stress induces the expression of a variety of genes in plants. However, the signal transduction pathway(s) that activates gene expression under cold stress is poorly understood. Mutants defective in cold signaling should facilitate molecular analysis of plant responses to low temperature and eventually lead to the identification and cloning of a cold stress receptor(s) and intracellular signaling components. In this study, we characterize a plant mutant affected in its response to low temperatures. The Arabidopsis hos1-1 mutation identified by luciferase imaging causes superinduction of cold-responsive genes, such as RD29A, COR47, COR15A, KIN1, and ADH. Although these genes are also induced by abscisic acid, high salt, or polyethylene glycol in addition to cold, the hos1-1 mutation only enhances their expression under cold stress. Genetic analysis revealed that hos1-1 is a single recessive mutation in a nuclear gene. Our studies using the firefly luciferase reporter gene under the control of the cold-responsive RD29A promoter have indicated that cold-responsive genes can be induced by temperatures as high as 19 degrees C in hos1-1 plants. In contrast, wild-type plants do not express the luciferase reporter at 10 degrees C or higher. Compared with the wild type, hos1-1 plants are l ess cold hardy. Nonetheless, after 2 days of cold acclimation, hos1-1 plants acquired the same degree of freezing tolerance as did the wild type. The hos1-1 plants flowered earlier than did the wild-type plants and appeared constitutively vernalized. Taken together, our findings show that the HOS1 locus is an important negative regulator of cold signal transduction in plant cells and that it plays critical roles in controlling gene expression under cold stress, freezing tolerance, and flowering time.     

Overexpression of <i>IbSINA5</i> Increases Cold Tolerance through a CBF SINA-COR Mediated Module in Sweet Potato

Seven in absentia (SINA) family proteins play a central role in plant growth, development and resistance to abiotic stress. However, their biological function in plant response to cold stress is still largely unknown. In this work, a seven in absentia gene IbSINA5 was isolated from sweet potato. Quantitative real-time polymerase chain reaction (qRT-PCR) analyses demonstrated that IbSINA5 was ubiquitously expressed in various tissues and organs of sweet potato, with a predominant expression in fibrous roots, and was remarkably induced by cold, drought and salt stresses. Subcellular localization assays revealed that IbSINA5-GFP fusion protein was mainly localized in cytoplasm and nucleus. Overexpression of IbSINA5 in sweet potato led to dramatically improved resistance to cold stress in transgenic plants, which was associated with the up-regulated expression of IbCOR (cold-regulated) genes, increased proline production, and decreased malondialdehyde (MDA) and H₂O₂ accumulation in the leaves of transgenic plants. Furthermore, transient expression of IbCBF3, a C-repeat binding factor (CBF) gene, in the leaf protoplasts of wild type sweet potato plants up-regulated the expression of both IbSINA5 and IbCOR genes. Our results suggest that IbSINA5 could function as a positive regulator in the cold signaling pathway through a CBF-SINA-COR mediated module in sweet potato, and have a great potential to be used as a candidate gene for the future breeding of new plant species with improved cold resistance.     

Construction of the seed-coat cDNA microarray and screening of differentially expressed genes in barley

Proanthocyanidins are dimeric or polymeric conden-sation products of the flavonoids, including catechin,epicatechin or gallocatechin with leucocyanidin, leuco-pelargonidin or leucodelphinidin [1]. They are prominentcolorless compounds, and are found widely existed inthe bark of trees, leaves, fruits, flowers and seed coats.They have many natural functions, such as antioxidantproperties [2] and insect resistance [3]. In forage, theycan bind and precipitate dietary proteins, thus protectthe anim…     

Arabidopsis thaliana mutant that develops as a light-grown plant in the absence of light

The signal transduction pathways that lead to chloroplast biogenesis in plants are largely unknown. We describe here the identification and initial characterization of a novel genetic locus which fits the criteria of a regulatory gene located in a central pathway controlling light-mediated development. In the absence of light, these Arabidopsis thaliana mutants, designated det1 (de-etiolated 1), constitutively display many characteristics that are light-dependent in wild-type plants, including leaf and chloroplast development, anthocyanin accumulation, and accumulation of mRNAs for several light-regulated nuclear and chloroplast genes. The switch between dark and light growth modes thus appears to be a programmed step in a developmental pathway that is defined by det1. We suggest a model where the primary role of light on gene expression is mediated by the activation of leaf development. Further, the recessive nature of the det1 mutation implies that there is negative growth control on leaf development in dicotyledonous plants in the absence of light.     

Screening for cold-resistant tomato under radiation mutagenesis and observation of the submicroscopic structure

Tomato is a cold-sensitive crop that is vulnerable to chilling injury. To screen for chilling resistance in tomato mutants, seeds were irradiated with different doses of ⁶⁰Co-γ and then evaluated according to the five stages of the chilling injury index. Moreover, physiological indexes and observation of the submicroscopic structure by electron microscopy were used to examine cold resistance in the mutants. The physiological index results showed much higher cold resistance in the mutants compared to wild type. The cellular structures of the cold-resistant mutants were more complete than in wild-type plants after chilling treatment. The chloroplasts of the mutants were close to the cell periphery; the double membrane structure of the chloroplast was intact, and well-developed granal stacks were interconnected by stroma. Compared to wild-type plants, the stomatal density of cold-resistant mutants increased considerably, though the stomatal size showed no obvious changes.     

A Subset of Cytokinin Two-component Signaling System Plays a Role in Cold Temperature Stress Response in Arabidopsis

A multistep two-component signaling system is established as a key element of cytokinin signaling in Arabidopsis. Here, we provide evidence for a function of the two-component signaling system in cold stress response in Arabidopsis. Cold significantly induced the expression of a subset of A-type ARR genes and of GUS in Pro_ARR7:GUS transgenic Arabidopsis. AHK2 and AHK3 were found to be primarily involved in mediating cold to express A-type ARRs despite cytokinin deficiency. Cold neither significantly induced AHK2 and AHK3 expression nor altered the cytokinin contents of wild type within the 4 h during which the A-type ARR genes exhibited peak expression in response to cold, indicating that cold might induce ARR expression via the AHK2 and AHK3 proteins without alterations in cytokinin levels. The ahk2 ahk3 and ahk3 ahk4 mutants exhibited enhanced freezing tolerance compared with wild type. These ahk double mutants acclimated as efficiently to cold as did wild type. The overexpression of the cold-inducible ARR7 in Arabidopsis resulted in a hypersensitivity response to freezing temperatures under cold-acclimated conditions. The expression of C-repeat/dehydration-responsive element target genes was not affected by ARR7 overexpression as well as in ahk double mutants. By contrast, the arr7 mutants showed increased freezing tolerance. The ahk2 ahk3 and arr7 mutants showed hypersensitive response to abscisic acid (ABA) for germination, whereas ARR7 overexpression lines exhibited insensitive response to ABA. These results suggest that AHK2 and AHK3 and the cold-inducible A-type ARRs play a negative regulatory role in cold stress signaling via inhibition of ABA response, occurring independently of the cold acclimation pathway.     

Ectopic expression of a cold-inducible transcription factor, CBF1/DREB1b, in transgenic rice (Oryza sativa L.)

The gene encoding C-repeat/dehydration-responsive element binding factor 1 (CBF1/DREB1b) of Arabidopsis was introduced into rice (Oryza sativa L.) under the control of the maize ubiquitin promoter. Its incorporation and expression in transgenic rice plants were confirmed by DNA and RNA gel-blot analyses. Cold tolerance in the transgenics was not significantly different from that of the wild-type plants, as determined by ion leakage, chlorophyll fluorescence, and survival rates. However, the cold-responsive genes lip5, lip9, and OsDhn1 were up-regulated in the transgenic plants, suggesting that the cold signal transduction pathway involving CBF1 is partially conserved in this cold-labile plant.     

A universal role for inositol 1,4,5-trisphosphate-mediated signaling in plant gravitropism

Inositol 1,4,5-trisphosphate (InsP3) has been implicated in the early signaling events of plants linking gravity sensing to the initiation of the gravitropic response. However, at present, the contribution of the phosphoinositide signaling pathway in plant gravitropism is not well understood. To delineate the role of InsP3 in plant gravitropism, we generated Arabidopsis (Arabidopsis thaliana) plants constitutively expressing the human type I inositol polyphosphate 5-phosphatase (InsP 5-ptase), an enzyme that specifically hydrolyzes InsP3. The transgenic plants show no significant differences in growth and life cycle compared to wild-type plants, although basal InsP3 levels are reduced by greater than 90% compared to wild-type plants. With gravistimulation, InsP3 levels in inflorescence stems of transgenic plants show no detectable change, whereas in wild-type plant inflorescences, InsP3 levels increase approximately 3-fold within the first 5 to 15 min of gravistimulation, preceding visible bending. Furthermore, gravitropic bending of the roots, hypocotyls, and inflorescence stems of the InsP 5-ptase transgenic plants is reduced by approximately 30% compared with the wild type. Additionally, the cold memory response of the transgenic plants is attenuated, indicating that InsP3 contributes to gravisignaling in the cold. The transgenic roots were shown to have altered calcium sensitivity in controlling gravitropic response, a reduction in basipetal indole-3-acetic acid transport, and a delay in the asymmetric auxin-induced beta-glucuronidase expression with gravistimulation as compared to the controls. The compromised gravitropic response in all the major axes of growth in the transgenic Arabidopsis plants reveals a universal role for InsP3 in the gravity signal transduction cascade of plants.     

A novel cold-regulated gene from Phlox subulata, PsCor413im1, enhances low temperature tolerance in Arabidopsis

Low temperature stress adversely affects plant growth, development, and crop productivity. Analysis of the function of genes in the response of plants to low temperature stress is essential for understanding the mechanism of chilling and freezing tolerance. In this study, PsCor413im1, a novel cold-regulated gene isolated from Phlox subulata, was transferred to Arabidopsis to investigate its function under low temperature stress. Real-time quantitative PCR analysis revealed that PsCor413im1 expression was induced by cold and abscisic acid. Subcellular localization revealed that PsCor413im1-GFP fusion protein was localized to the periphery of the chloroplast, consistent with the localization of chloroplast inner membrane protein AtCor413im1, indicating that PsCor413im1 is a chloroplast membrane protein. Furthermore, the N-terminal of PsCor413im1 was determined to be necessary for its localization. Compared to the wild-type plants, transgenic plants showed higher germination and survival rates under cold and freezing stress. Moreover, the expression of AtCor15 in transgenic plants was higher than that in the wild-type plants under cold stress. Taken together, our results suggest that the overexpression of PsCor413im1 enhances low temperature tolerance in Arabidopsis.