Wild-type Arabidopsis seedlings are capable of following two developmental programs: photomorphogenesis in the light and skotomorphogenesis in darkness. Screening of Arabidopsis mutants for constitutive photomorphogenic development in darkness resulted in the identification of three new loci designated COP8, COP10, and COP11. Detailed examination of the temporal morphological and cellular differentiation patterns of wild-type and mutant seedlings revealed that in darkness, seedlings homozygous for recessive mutations in COP8, COP10, and COP11 failed to suppress the photomorphogenic developmental pathway and were unable to initiate skotomorphogenesis. As a consequence, the mutant seedlings grown in the dark had short hypocotyls and open and expanded cotyledons, with characteristic photomorphogenic cellular differentiation patterns and elevated levels of light-inducible gene expression. In addition, plastids of dark-grown mutants were defective in etioplast differentiation. Similar to cop1 and cop9, and in contrast to det1 (deetiolated), these new mutants lacked dark-adaptive change of light-regulated gene expression and retained normal phytochrome control of seed germination. Epistatic analyses with the long hypocotyl hy1, hy2, hy3, hy4, and hy5 mutations suggested that these three loci, similar to COP1 and COP9, act downstream of both phytochromes and a blue light receptor, and probably HY5 as well. Further, cop8-1, cop10-1, and cop11-1 mutants accumulated higher levels of COP1, a feature similar to the cop9-1 mutant. These results suggested that COP8, COP10, and COP11, together with COP1, COP9, and DET1, function to suppress the photomorphogenic developmental program and to promote skotomorphogenesis in darkness. The identical phenotypes resulting from mutations in COP8, COP9, COP10, and COP11 imply that their encoded products function in close proximity, possibly with some of them as a complex, in the same signal transduction pathway. 相似文献
DNA at the FMR-1 locus was analyzed by Southern blot using probe StB12.3 in an unusual fragile X family with six brothers, three of whom are affected with fragile X to varying degrees, two of whom are nonpenetrant carriers, and one of whom is unaffected. Fragile X chromosome studies, detailed physical examinations, and psychological testing were completed on all six. Two of the affected brothers and the two nonpenetrant brothers were found to be methylation mosaics. The three affected males spanned the phenotypic and cognitive spectrum of the fragile X syndrome. A correlation was seen between the degree of methylation and the phenotypic expression identified in the three affected males. The two males initially classified as nonpenetrant were found to have mild phenotypic expression which consisted of minor cognitive deficits and a partial physical phenotype. These two, who were negative on fragile X chromosome studies, were found on DNA analysis to have large broad smears, with approximately 97% of the DNA unmethylated. The results described here indicate that some "nonpenetrant" carrier males may have varying amounts of methylation of the FMR-1 region, which can result in mild expression of the fragile X syndrome. The apparently mild phenotypic and cognitive expression of the fragile X syndrome in the two males, initially classified as nonpenetrant, who are mosaic for hypermethylation of an expansion of the CGG repeat in the premutation range, indicates that expression of the syndrome is not confined to males with large, hypermethylated expansions (full mutation) but has instead a gradient effect with a threshold for the full expression of the phenotype. 相似文献
Gating of associations of mechanosensitive Ca2+-selective cation co-channels in the plasmalemma of onion epidermis has a strong and unusual temperature dependence. Tension-dependent activity rises steeply as temperature is lowered from 25°C to about 6°C, but drops to a low level at about 5°C. Under the conditions tested (with Mg2+ and K+ at the cytosolic face of outside-out membrane patches), promotion results both from more bursting at all observed linkage levels and from longer duration of bursts of co-channels linked as quadruplets and quintuplets. Co-channel conductance decreases linearly, but only modestly, with declining temperature. It is proposed that these and related mechanosensitive channels may participate in a variety of responses to temperature, including thermonasty, thermotropism, hydrotropism, and both cold damage and cold acclimation. 相似文献
Mature leaves of a transgenic tobacco plant ( Nicotiana tabacum L var. Samsun, line A41-10) that constitutively express a yeast-derived acid invertase gene develop symptoms which are characterized by the presence of greenish-yellow and green sectors in the same leaf, and onset of early, leaf senescence. Previous studies indicated that invertase activity was two- to threefold higher in the greenish-yellow sectors than in the green sectors. Our structural analyses revealed that development of secondary plasmodesmata, via modification of existing primary plasmodesmata, between mesophyll cells was inhibited severely in the greenish-yellow sectors, but only marginally in the green sectors. In contrast, the structure and function of primary plasmodesmata in the same symptomatic sectors remained unaltered as determined by structural and dye coupling studies. It is hypothesized that secondary plasmodesmata differ from primary plasmodesmata in having special abilities to traffic information molecules to coordinate leaf development and physiological function(s). Arrest of secondary plasmodesmal development by high invertase activity in the transgenic tobacco leaf may have prevented this type of trafficking and hence resulted in early leaf senescence. The results also indicate that the yeast acid invertase-expressing tobacco may provide an effective experimental system for the molecular characterization of cellular mechanisms that regulate the development, function, and possible turnover of secondary plasmodesmata. 相似文献
Polyethylene terephthalate (PET) hydrolase enzymes show promise for enzymatic PET degradation and green recycling of single-use PET vessels representing a major source of global pollution. Their full potential can be unlocked with enzyme engineering to render activities on recalcitrant PET substrates commensurate with cost-effective recycling at scale. Thermostability is a highly desirable property in industrial enzymes, often imparting increased robustness and significantly reducing quantities required. To date, most engineered PET hydrolases show improved thermostability over their parental enzymes. Here, we report engineered thermostable variants of Ideonella sakaiensis PET hydrolase enzyme (IsPETase) developed using two scaffolding strategies. The first employed SpyCatcher-SpyTag technology to covalently cyclize IsPETase, resulting in increased thermostability that was concomitant with reduced turnover of PET substrates compared to native IsPETase. The second approach using a GFP-nanobody fusion protein (vGFP) as a scaffold yielded a construct with a melting temperature of 80°C. This was further increased to 85°C when a thermostable PETase variant (FAST PETase) was scaffolded into vGFP, the highest reported so far for an engineered PET hydrolase derived from IsPETase. Thermostability enhancement using the vGFP scaffold did not compromise activity on PET compared to IsPETase. These contrasting results highlight potential topological and dynamic constraints imposed by scaffold choice as determinants of enzyme activity. 相似文献
Low-temperature and high humidity are typical environmental factors in the plastic tunnel and solar greenhouse during the cold season that restricts plant growth and development. Herein, we investigated the impact of different combinations of low-temperature and high humidity (day/night: T1 15/10 °C?+?95%, T2 12/8 °C?+?95%, and T3 9/5 °C?+?95%) along with a control (CK 25/18 °C?+?80%) on cucumber cultivars viz: Zhongnong37 (ZN37: resistant) and Shuyanbailv (SYB: sensitive). The low-temperature and high humidity stresses increased electrolyte leakage (EL), malondialdehyde (MDA), hydrogen peroxide (H2O2) and intercellular concentration of carbon dioxide (Ci), and reduced morphological indices, relative water content (RWC), net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (E) and leaf pigments in both cultivars as compared to control (CK). Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were decreased in cv. SYB under stress conditions as compared to cv. ZN37. Low-temperature and high humidity treatments showed an increase in proline and soluble protein content in cv. ZN37 as compared to cv. SYB. Abscisic acid (ABA) and jasmonic acid (JA) were augmented while indole-3-acetic acid (IAA), zeatin (ZT), zeatin riboside (ZR), and gibberellic acid (GA) were decreased in both cultivars. Under T3 (9/5 °C?+?95%), Pn, protoporphyrin, and ZT were extremely decreased by 71.3%, 74.3%, and 82.4%, respectively, in cv. SYB compared to control. Moreover, principal component analysis (PCA) based on physiochemical traits confirmed that cv. ZN37 had the strongest correlation with antioxidant enzymes, proline, and soluble protein content than cv. SYB under low-temperature and high humidity treatments. Our results suggest that a stress-tolerant cultivar mitigates stress damage in cucumber transplants by regulating photosynthetic efficiency, antioxidant capacity and hormonal profile when compared to a stress-sensitive cultivar.