Draft genome analysis provides insights into the fiber yield, crude protein biosynthesis, and vegetative growth of domesticated ramie (Boehmeria nivea L. Gaud).

Plentiful bast fiber, a high crude protein content, and vigorous vegetative growth make ramie a popular fiber and forage crop. Here, we report the draft genome of ramie, along with a genomic comparison and evolutionary analysis. The draft genome contained a sequence of approximately 335.6 Mb with 42,463 predicted genes. A high-density genetic map with 4,338 single nucleotide polymorphisms (SNPs) was developed and used to anchor the genome sequence, thus, creating an integrated genetic and physical map containing a 58.2-Mb genome sequence and 4,304 molecular markers. A genomic comparison identified 1,075 unique gene families in ramie, containing 4,082 genes. Among these unique genes, five were cellulose synthase genes that were specifically expressed in stem bark, and 3 encoded a WAT1-related protein, suggesting that they are probably related to high bast fiber yield. An evolutionary analysis detected 106 positively selected genes, 22 of which were related to nitrogen metabolism, indicating that they are probably responsible for the crude protein content and vegetative growth of domesticated varieties. This study is the first to characterize the genome and develop a high-density genetic map of ramie and provides a basis for the genetic and molecular study of this crop.

Characterization and thermal inactivation kinetics of highly thermostable ramie leaf ß-amylase.

We characterized ramie leaf ß-amylase, and determined its thermostability and kinetic parameters. The enzyme was purified 53-fold using ammonium sulfate fractionation (40-60% saturation), anion exchange chromatography on DEAE-cellulose and gel permeation chromatography on Superdex-200. The purified enzyme was identified as ß-amylase with molecular mass of 42kD. The enzyme displayed Km and kcat values for soluble potato starch of 1.1mg/mL and 7.8s-1, respectively. The enzyme had a temperature optimum of 65°C, and its activity at 70°C was 92% of that at the optimal temperature after a 15-min incubation. Furthermore, enzyme activity was stable during treatment at 55°C for 60min but was inactivated rapidly at >75°C. This thermal behavior indicates that ramie leaf ß-amylase has excellent intermediate temperature-stable enzyme properties for the baking and bio-industries. Inactivation of the enzyme followed first-order kinetics in the range of 55-80°C. The enthalpy change of thermal inactivation (ΔH‡), ΔG‡, and ΔS‡ were 237.2kJ/mol, 107.7kJ/mol, and 0.39kJ/molK at 333K, respectively. The D-value at 65°C (=110min) and the z-value (=9.4°C) are given for food processing.

Effects of concentrations of sodium chloride on photosynthesis, antioxidative enzymes, growth and fiber yield of hybrid ramie.

Ramie (Boehmeria nivea L.) is one of the oldest and most important fiber crops in China due to the comfortable textile of its fine fiber. Increased ramie fiber demand brings ramie cultivation to salt-affected regions. The aim of this research was to determine morphological, physiological and biochemical responses of ramie by subjecting plants to varying concentrations of NaCl (0, 2, 4, 6 and 8 g NaCl/kg dry soil) at vigorous growth stage for 10 and 20 days. Results indicated that salinity stress substantially inhibited the growth of hybrid ramie plants and led to remarkable decline in fiber yield. However, when grown at 2 g NaCl/kg growth and fiber yield were similar to non-saline control. In addition, chlorophyll fluorescence and gas exchange parameters were correlated with growth and yield response. Salt treatments promoted a subsequent decrease in maximum quantum efficiency of PSII photochemistry (Fv/Fm), quantum efficiency of open PSII reaction centers (Fv'/Fm') and quantum yield of PSII (φPSII) while non-photochemical quenching (NPQ) changed conversely. Photochemical quenching (qP) and electron transport rate of PSII (ETR) increased at 2 and 4 g NaCl/kg then decreased at 6 and 8 g NaCl/kg. Substantial decline in the PSII activity at high salinity was associated with the loss of chlorophyll contents. Moreover, marked decrease in net photosynthetic rate (A), transpiration rate (E), stomatal conductance (gs) was also recorded. Nonetheless, intercellular CO2 (Ci) decreased at low salt stress, subsequently increased at high salt stress while water use efficiency (WUE) and instantaneous water use efficiency (WUEi) altered in opposite direction. Substantial decrease of photosynthesis at high salinity was due to non-stomatal factors. Furthermore, salinity stress led to decrease of proteins and accumulation of proline and malondialdehyde (MDA), as well as enhanced activities of superoxide dismutase (SOD, EC 1.15.1.1) and peroxidase (POD, EC 1.11.1.6), whereas, catalase (CAT, EC 1.11.1.7) enhanced at low salinity, decreased at high salinity. Nonetheless, these changes were closely related with the severity and duration of the salinity stress and their interaction. The results suggested a certain tolerance to salinity stress for hybrid ramie. This meets the essential condition for utilization in salinity-prone environments.