Occurrence and pathogenicity of Enterobacter sp. causing sprout decay and seedling stunting of upland cotton (Gossypium hirsutum L.)

A new sprout decay and seedling stunting disease of unknown aetiology in upland cotton (Gossypium hirsutum L.) affecting nearly 5%–10% of young seedlings was noticed in vertisols of central Vidarbha (Maharashtra state, India) in July of 2017. The bacterium was consistently isolated from diseased seedlings and identified with a polyphasic method of characterization, including morphological, physiological, biochemical and 16S rRNA gene sequence analysis. The bacterium strain CICR-MGMG1 was isolated from diseased plants identified as Enterobacter sp. Inoculation of healthy cotton seed with an axenic culture of strain CICR-MGMG1 isolated from diseased young seedling reproduced disease symptoms of yellowing, stunting and deformed growth similar to the symptoms reported from infected field condition. The strain CICR-MGMG1 was consistently isolated from both diseased seedlings and stunted plants. Thus, the pathogenicity test of Koch's postulates was confirmed with the bacterium Enterobacter sp. strain CICR-MGMG1 as the causal organism of sprout decay and seedling stunting. To the best of our knowledge, this is the first record of Enterobacter sp. causing sprouts decay and seedling stunting of cotton.     

Effects of diurnal temperature range on adult size and emergence times from diapausing pupae in Papilio glaucus and P. canadensis (Papilionidae)

Abstract With recent climate warming trends, both the increase in thermal variance (i.e., diurnal temperature range; DTR) as well as increased mean temperature may impact many different organisms, especially poikilothermic invertebrates. Predictions of insect developmental rates using degree‐days (thermal unit accumulations above the developmental base threshold of the insect) are based on daily mean temperatures, regardless of DTR. However, non‐linearity and variance in the means and extremes are often ignored. The role of thermal variance (e.g., daily temperature extremes and DTR) was evaluated experimentally for two swallowtail butterfly sister species using a common day/night photoperiod of 18: 6 h photo: scoto‐phase and corresponding daytime thermophase and nighttime cryophase periods of 22: 22°C (constant 22°C), 24: 16°C, and 26: 10°C (all three treatments had the same daily mean and the same degree‐day accumulations). Although developmental rates of post‐diapause pupae were largely unaffected for both species, our results show that sizes in P. canadensis females (but not males) were smaller in the treatments with more variance (26°C: 10°C) compared to constant 22°C. Such potentially significant impacts of size reduction in P. canadensis females were not observed in P. glaucus males or females under the same series of thermo‐period treatments.     

Patterns of phylogenetic beta diversity in China's grasslands in relation to geographical and environmental distance

Patterns and determinants of beta (β-) diversity can be used to explore the underlying mechanisms regulating community assembly. Despite being the most commonly used measure of β-diversity, species turnover does not consider the evolutionary differences among species, treating all species equally. Incorporating information on phylogenetic non-independence or relatedness among species in the calculation of β-diversity may substantially advance our understanding of the ecological and evolutionary mechanisms structuring communities. Here, we investigate the relative influence of geographical distance and differences in environmental conditions (environmental distance) on the phylogenetic β-diversity between grassland communities expanding 4000 km across the Tibetan Plateau, the Inner Mongolia Plateau and the Xinjiang Autonomous Region in China. Both observed and standardized effect size of phylogenetic β-diversity were significantly correlated with geographical and environmental distance across all regions. However, the effect of geographical distance on the standardized effect size of phylogenetic β-diversity disappeared when environmental distance was controlled. We also found that within different regions, the effect of environmental distance on both observed and standardized effect size of phylogenetic β-diversity was more significant than geographical distance. Among environmental variables, climate played a more important role in shaping observed phylogenetic β-diversity across and within regions, and standardized effect size of phylogenetic β-diversity across regions. Soil properties played a more important role in shaping standardized effect size of phylogenetic β-diversity within regions. The phylogenetic β-diversity of species from dicot and monocot clades exhibited similar patterns along environmental and geographical distance. The results suggest that at the study scale, phylogeny of grassland communities in China is predominantly structured by environmental filtering, and the dominant environmental factors may be scale-dependent.     

Interactions of barley α-amylase isozymes with Ca2 + , substrates and proteinaceous inhibitors

α-Amylases are endo-acting retaining enzymes of glycoside hydrolase family 13 with a catalytic (β/α)₈-domain containing an inserted loop referred to as domain B and a C-terminal anti-parallel β-sheet termed domain C. New insights integrate the roles of Ca^2?+?, different substrates, and proteinaceous inhibitors for α-amylases. Isozyme specific effects of Ca^2?+? on the 80% sequence identical barley α-amylases AMY1 and AMY2 are not obvious from the two crystal structures, containing three superimposable Ca^2?+? with identical ligands. A fully hydrated fourth Ca^2?+? at the interface of the AMY2/barley α-amylase/subtilisin inhibitor (BASI) complex interacts with catalytic groups in AMY2, and Ca^2?+? occupies an identical position in AMY1 with thiomaltotetraose bound at two surface sites. EDTA-treatment, DSC, and activity assays indicate that AMY1 has the highest affinity for Ca^2?+?. Subsite mapping has revealed that AMY1 has ten functional subsites which can be modified by means protein engineering to modulate the substrate specificity. Other mutational analyses show that surface carbohydrate binding sites are critical for interaction with polysaccharides. The conserved Tyr380 in the newly discovered ‘sugar tongs’ site in domain C of AMY1 is thus critical for binding to starch granules. Furthermore, mutations of binding sites mostly reduced the degree of multiple attack in amylose hydrolysis. AMY1 has higher substrate affinity than AMY2, but isozyme chimeras with AMY2 domain C and other regions from AMY1 have higher substrate affinity than both parent isozymes. The latest revelations addressing various structural and functional aspects that govern the mode of action of barley α-amylases are reported in this review.