yucca6, a dominant mutation in Arabidopsis, affects auxin accumulation and auxin-related phenotypes

Auxin plays critical roles in many aspects of plant growth and development. Although a number of auxin biosynthetic pathways have been identified, their overlapping nature has prevented a clear elucidation of auxin biosynthesis. Recently, Arabidopsis (Arabidopsis thaliana) mutants with supernormal auxin phenotypes have been reported. These mutants exhibit hyperactivation of genes belonging to the YUCCA family, encoding putative flavin monooxygenase enzymes that result in increased endogenous auxin levels. Here, we report the discovery of fertile dominant Arabidopsis hypertall1-1D and hypertall1-2D (yucca6-1D, -2D) mutants that exhibit typical auxin overproduction phenotypic alterations, such as epinastic cotyledons, increased apical dominance, and curled leaves. However, unlike other auxin overproduction mutants, yucca6 plants do not display short or hairy root phenotypes and lack morphological changes under dark conditions. In addition, yucca6-1D and yucca6-2D have extremely tall (>1 m) inflorescences with extreme apical dominance and twisted cauline leaves. Microarray analyses revealed that expression of several indole-3-acetic acid-inducible genes, including Aux/IAA, SMALL AUXIN-UP RNA, and GH3, is severalfold higher in yucca6 mutants than in the wild type. Tryptophan (Trp) analog feeding experiments and catalytic activity assays with recombinant YUCCA6 indicate that YUCCA6 is involved in a Trp-dependent auxin biosynthesis pathway. YUCCA6:GREEN FLUORESCENT PROTEIN fusion protein indicates YUCCA6 protein exhibits a nonplastidial subcellular localization in an unidentified intracellular compartment. Taken together, our results identify YUCCA6 as a functional member of the YUCCA family with unique roles in growth and development.     

AtHKT1 facilitates Na+ homeostasis and K+ nutrition in planta

Genetic and physiological data establish that Arabidopsis AtHKT1 facilitates Na(+) homeostasis in planta and by this function modulates K(+) nutrient status. Mutations that disrupt AtHKT1 function suppress NaCl sensitivity of sos1-1 and sos2-2, as well as of sos3-1 seedlings grown in vitro and plants grown in controlled environmental conditions. hkt1 suppression of sos3-1 NaCl sensitivity is linked to higher Na(+) content in the shoot and lower content of the ion in the root, reducing the Na(+) imbalance between these organs that is caused by sos3-1. AtHKT1 transgene expression, driven by its innate promoter, increases NaCl but not LiCl or KCl sensitivity of wild-type (Col-0 gl1) or of sos3-1 seedlings. NaCl sensitivity induced by AtHKT1 transgene expression is linked to a lower K(+) to Na(+) ratio in the root. However, hkt1 mutations increase NaCl sensitivity of both seedlings in vitro and plants grown in controlled environmental conditions, which is correlated with a lower K(+) to Na(+) ratio in the shoot. These results establish that AtHKT1 is a focal determinant of Na(+) homeostasis in planta, as either positive or negative modulation of its function disturbs ion status that is manifested as salt sensitivity. K(+)-deficient growth of sos1-1, sos2-2, and sos3-1 seedlings is suppressed completely by hkt1-1. AtHKT1 transgene expression exacerbates K(+) deficiency of sos3-1 or wild-type seedlings. Together, these results indicate that AtHKT1 controls Na(+) homeostasis in planta and through this function regulates K(+) nutrient status.     

The helminth fauna of wild and domestic ruminants in Mongolia—a review

The helminth fauna of eight species of wild ruminants and five species of domestic ruminants sharing common grassland in Mongolia was reviewed. A total of 108 species of helminths, belonging to 40 genera, 23 families, 11 superfamilies, 6 orders and 3 classes were reported in wild and domestic ruminants in Mongolia. Several new host–helminth associations have been recorded. Twenty seven helminth species have been found in certain host species for the first time in Mongolia. These included 2 species of trematodes, 2 species of cestodes and 23 species of nematodes. Helminths that are specific for some of the examined ruminant species were determined. However, wild animals may serve as a reservoir of helminth infections for domestic animals when sharing grassland in Mongolia. The helminth fauna of the ruminants with respect to occurrence, distribution, prevalence and intensity of infection was considered for six geographic regions of Mongolia.     

Effects of open-top passive warming chambers on soil respiration in the semi-arid steppe to taiga forest transition zone in Northern Mongolia

The response of soil respiration to warming has been poorly studied in regions at higher latitude with low precipitation. We manipulated air temperature, soil temperature and soil moisture using passive, open-top chambers (OTCs) in three different ecosystem settings in close proximity (boreal forest, riparian area, and semi-arid steppe) to investigate how environmental factors would affect soil respiration in these different ecosystems, anticipating that soil respiration would increase in response to the chamber treatment. The results indicated that OTCs significantly increased air and soil temperature in areas with open canopy and short-statured vegetation (i.e., steppe areas) but not in forest. OTCs also affected soil moisture, but the direction of change depended on the ecosystem, and the magnitude of change was highly variable. Generally, OTCs did not affect soil respiration in steppe and riparian areas. Although soil respiration was slightly greater in OTCs placed in the forest, the difference was not statistically significant. Analyses of relationships between soil respiration and environmental variables suggested that different factors controlled soil respiration in the different ecosystems. Competing effects analysis using a model selection approach and regression analyses (e.g., Q₁₀) demonstrated that soil respiration in the forest was more sensitive to warming, while soil respiration in the steppe was more sensitive to soil moisture. The differing responses and controlling factors among these neighboring forest, riparian and steppe ecosystems in Northern Mongolia highlight the importance of taking into account potential biome shifts in C cycling modeling to generate more accurate predictions of landscape-scale responses to anticipated climate change.