University of Georgia

About: University of Georgia is a education organization based out in Athens, Georgia, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 41934 authors who have published 93622 publications receiving 3713212 citations. The organization is also known as: UGA & Franklin College.

MYB58 and MYB63 are transcriptional activators of the lignin biosynthetic pathway during secondary cell wall formation in Arabidopsis.

Abstract: It has previously been shown that SECONDARY WALL–ASSOCIATED NAC DOMAIN PROTEIN1 (SND1) is a key transcription factor regulating secondary cell wall formation, including the biosynthesis of cellulose, xylan, and lignin. In this study, we show that two closely related SND1-regulated MYB transcription factors, MYB58 and MYB63, are transcriptional regulators specifically activating lignin biosynthetic genes during secondary wall formation in Arabidopsis thaliana. MYB58 and MYB63 are phylogenetically distinct from previously characterized MYBs shown to be associated with secondary wall formation or phenylpropanoid metabolism. Expression studies showed that MYB58 and MYB63 are specifically expressed in fibers and vessels undergoing secondary wall thickening. Dominant repression of their functions led to a reduction in secondary wall thickening and lignin content. Overexpression of MYB58 and MYB63 resulted in specific activation of lignin biosynthetic genes and concomitant ectopic deposition of lignin in cells that are normally unlignified. MYB58 was able to activate directly the expression of lignin biosynthetic genes and a secondary wall–associated laccase (LAC4) gene. Furthermore, the expression of MYB58 and MYB63 was shown to be regulated by the SND1 close homologs NST1, NST2, VND6, and VND7 and their downstream target MYB46. Together, our results indicate that MYB58 and MYB63 are specific transcriptional activators of lignin biosynthesis in the SND1-mediated transcriptional network regulating secondary wall formation.

Water-Stable Aggregates and Organic Matter Fractions in Conventional- and No-Tillage Soils

Abstract: No-tillage (NT) practices can improve soil aggregation and change the distribution and retention of soil organic matter (SOM) compared with conventional tillage (CT), but the relationships between aggregates and SOM fractions are poorly known. The effects of long-term (13-yr) CT and NT management on water-stable aggregates (WSA) and aggregate-associated SOM were investigated on a Hiwassee sandy clay loam (clayey, kaolinitie, thermic Rhodic Kanhapludult). Samples were collected at two depths in replicated CT and NT plots and separated into five aggregate size classes by wet sieving. The stability of intact WSA was measured turbidimetrically. The C and N content of total, participate (POM), and mineral-associated organic matter was determined for each size class. Whole-soil organic C was 18% higher in NT (30.7 Mg C ha-») than in CT (26.1 Mg C ha"). In CT, macroaggregates (>250 um) were fewer and less stable than those of NT. The POM C made up = 36% of whole soil C regardless of tillage, but the quantity of POM was nearly 20% higher in NT than in CT. The POM comprised a higher percentage of total aggregate N in surface soils of NT than in CT and values increased with increases in aggregate size. In NT, concentrations of total and mineral-associated C and N were higher in the 106to 250-|im WSA than in the other size classes but, in CT, the concentrations were similar among size classes. An alternative view of aggregate organization is discussed in which microaggregates are formed in association with POM at the center of macroaggregates, helping to explain relationships between SOM storage and aggregate size distributions under different management practices. C of soils results in the disruption of soil aggregates and the loss of SOM compared with native sod and pasture soils (van Veen and Paul, 1981; Tisdall and Oades, 1982; Elliott, 1986; Kay, 1990). Under CT practices, plowing, harrowing, and rotary tillage result in mixing of the soil profile and the fragmentation and burial of crop residues. These effects tend to moderate the fluctuations of temperature and water in buried residues and increase their proximity to mineral nutrients, thereby enhancing residue decomposition and organic matter transformations (Blevins et al., 1984; Beare et al., 1992). With NT management, the soil is not plowed and crop residues accumulate on the soil surface as a mulch. Several studies have shown that if residues are not removed, NT management can improve soil aggregation and reduce losses of SOM that result from cultivation (Havlinetal., 1990; Carter, 1992; Weill et al,, 1989). However, other studies report few changes in soil aggregation (Hamblin, 1980) and no effects on SOM content other than changes in the depth distribution of SOM with plowing (Angers et al., 1992; Carter and Rennie, 1982). M.H. Beare, Inst. for Crop and Food Research (Lincoln), Private Bag 4704, Christchurch, New Zealand; and P.P. Hendrix, Dep. of Agronomy and Inst. of Ecology, and D.C. Coleman, Inst. of Ecology, Univ. of Georgia, Athens, GA 30602. Received 8 Mar. 1993. Corresponding author. Published in Soil Sci. Soc. Am. J. 58:777-786 (1994). Kaolinitie soils of the southeast USA are characterized by high dispersibility, a factor that may increase the susceptibility of cultivated soils to aggregate disruption, surface crusting, reduced infiltration, and erosion (Miller and Baharuddin, 1986; Sumner, 1992). In warm humid climatic regimes, these factors can contribute to rapid losses of SOM and a decline in the productivity of agricultural soils (Giddens, 1957; Bruce et al., 1990b; Sanchez et al., 1989). Many studies have investigated relationships between whole SOM and WSA (e.g., Chaney and Swift, 1984; Kemper and Koch, 1966; Angers et al., 1992), but relatively few have attempted to isolate and characterize the SOM associated with WSA (Dormaar, 1983; Baldock et al., 1987; Monrozier et al., 1991). Knowledge of aggregate-associated SOM may be important to understanding how changes in aggregation under different tillage and residue management practices contribute to the accumulation and loss of SOM (Elliott, 1986; Gupta and Germida, 1988). These relationships are largely unknown for soils of the southeastern USA. Furthermore, understanding these relationships is crucial for evaluating the applicability of the hierarchical model of aggregate organization (Tisdall and Oades, 1982) to a broader range of soils and management conditions. Both physical and chemical methods have been used to fractionate and characterize SOM. Although the limitations of these individual techniques are well known (Elliott and Cambardella, 1991; Duxbury et al., 1989), various combinations of physical and chemical separation techniques have been used to successfully characterize the chemical composition of primary organo-mineral particle-size fractions (Turchenek and Oades, 1979; Andersonetal., 1981; Tiessen and Stewart, 1983). Cambardella and Elliott (1992) recently described a simple method combining chemical dispersion with particle-size separation to isolate and subsequently characterize particulate and mineral-associated organic matter of native sod and agricultural soils from the Great Plains. Their results suggest that whole soil POM accounts for much of the SOM lost with cultivation of native sod and that NT practices can significantly reduce these losses. In this study, we combined wet-sieving techniques for the isolation of WSA with the chemical dispersion and physical separation methods of Cambardella and Elliott (1992) to investigate relationships between soil aggregation and the location and composition of aggregateassociated SOM in CT and NT soils. Our objectives were to describe the effects of long-term CT and NT management of a double-cropped soil on (i) the size Abbreviations: NT, no-tillage; SOM, soil organic matter; CT, conventional-tillage; WSA, water-stable aggregates; POM, paniculate organic matter; HSB, Horseshoe Bend Experimental Area; FLPOM, floating particulate organic matter; ASI, aggregate stability index; ANOVA, analysis of variance. 777 Published May, 1994

The contribution of headwater streams to biodiversity in river networks

Abstract: The diversity of life in headwater streams (intermittent, first and second order) contributes to the biodiversity of a river system and its riparian network. Small streams differ widely in physical, chemical, and biotic attributes, thus providing habitats for a range of unique species. Headwater species include permanent residents as well as migrants that travel to headwaters at particular seasons or life stages. Movement by migrants links headwaters with downstream and terrestrial ecosystems, as do exports such as emerging and drifting insects.

Measuring the Demand for Environmental Quality

Abstract: Part I: Theory and Methods. Introduction (J.B. Braden, C.D. Kolstad and D. Miltz). Environmental Demand Theory (C.D. Kolstad and J.B. Braden). Household Production Functions and Environmental Benefit Estimation (V.K. Smith). Hedonic Methods (R.B. Palmquist). Constructed Markets (R.T. Carson). Part II: Methods for Valuing Classes of Environmental Effects. Environmental Health Effects (M.L. Cropper and A.M. Freeman III). Aesthetics (P.E. Graves). Recreation (N.E. Bockstael, K.E. McConnell and I. Strand). Materials Damages (R.M. Adams and T.D. Crocker). Total and Nonuse Values (A. Randall). Summary and Conclusions (J.B. Braden and C.D. Kolstad). Bibliography. Author Index. Subject Index.

A review of the global burden, novel diagnostics, therapeutics, and vaccine targets for cryptosporidium

Abstract: Summary Cryptosporidium spp are well recognised as causes of diarrhoeal disease during waterborne epidemics and in immunocompromised hosts. Studies have also drawn attention to an underestimated global burden and suggest major gaps in optimum diagnosis, treatment, and immunisation. Cryptosporidiosis is increasingly identified as an important cause of morbidity and mortality worldwide. Studies in low-resource settings and high-income countries have confirmed the importance of cryptosporidium as a cause of diarrhoea and childhood malnutrition. Diagnostic tests for cryptosporidium infection are suboptimum, necessitating specialised tests that are often insensitive. Antigen-detection and PCR improve sensitivity, and multiplexed antigen detection and molecular assays are underused. Therapy has some effect in healthy hosts and no proven efficacy in patients with AIDS. Use of cryptosporidium genomes has helped to identify promising therapeutic targets, and drugs are in development, but methods to assess the efficacy in vitro and in animals are not well standardised. Partial immunity after exposure suggests the potential for successful vaccines, and several are in development; however, surrogates of protection are not well defined. Improved methods for propagation and genetic manipulation of the organism would be significant advances.