In silico identification and characterization of N-Terminal acetyltransferase genes of poplar (Populus trichocarpa).

N-terminal acetyltransferase (Nats) complex is responsible for protein N-terminal acetylation (Nα-acetylation), which is one of the most common covalent modifications of eukaryotic proteins. Although genome-wide investigation and characterization of Nat catalytic subunits (CS) and auxiliary subunits (AS) have been conducted in yeast and humans they remain unexplored in plants. Here we report on the identification of eleven genes encoding eleven putative Nat CS polypeptides, and five genes encoding five putative Nat AS polypeptides in Populus. We document that the expansion of Nat CS genes occurs as duplicated blocks distributed across 10 of the 19 poplar chromosomes, likely only as a result of segmental duplication events. Based on phylogenetic analysis, poplar Nat CS were assigned to six subgroups, which corresponded well to the Nat CS types (CS of Nat A-F), being consistent with previous reports in humans and yeast. In silico analysis of microarray data showed that in the process of normal development of the poplar, their Nat CS and AS genes are commonly expressed at one relatively low level but share distinct tissue-specific expression patterns. This exhaustive survey of Nat genes in poplar provides important information to assist future studies on their functional role in poplar.

PagWOX11/12a from hybrid poplar enhances drought tolerance by modulating reactive oxygen species.

WOX11/12 is a homeobox gene of WOX11 and WOX12 in Arabidopsis that plays important roles in crown root development and growth. It has been reported that WOX11/12 participates in adventitious root (AR) formation and different abiotic stress responses, but the downstream regulatory network of WOX11/12 in poplar remains to be further investigated. In this study, we found that PagWOX11/12a is strongly induced by PEG-simulated drought stress. PagWOX11/12a-overexpressing poplar plantlets showed lower oxidative damage levels, greater antioxidant enzyme activities and reactive oxygen species (ROS) scavenging capacity than non-transgenic poplar plants, whereas PagWOX11/12a dominant repression weakened root biomass accumulation and drought tolerance in poplar. RNA-seq analysis revealed that several differentially expressed genes (DEGs) regulated by PagWOX11/12a are involved in redox metabolism and drought stress response. We used RT-qPCR and yeast one-hybrid (Y1H) assays to validate the downstream target genes of PagWOX11/12a. These results provide new insights into the biological function and molecular regulatory mechanism of WOX11/12 in the abiotic resistance processes of poplar.

Soil C, N and P stoichiometry in different forest stand types in the middle and lower reaches of the Beijiang River, China.

We examined the vertical distribution characteristics of soil organic carbon (C), total nitrogen (N), total phosphorus (P) and their ecological stoichiometric ratios in 0-80 cm soil profile under three forest stand types in the middle and lower reaches of the Beijiang River, including broad-leaved forest, coniferous forest, and mixed coniferous and broad-leaved forest. The results showed that soil C, N and P contents of the three forest stand types were 12.17-14.25, 1.14-1.31, and 0.27-0.30 g·kg-1, respectively. The contents of C and N decreased with the increases of soil depth. The content of C and N in each soil layer showed that coniferous and broad-leaved mixed forest > coniferous forest > broad-leaved forest. There was no significant difference in P content among the three stand types, and there was no obvious variation in the vertical profile. The soil C/N, C/P, and N/P of the three forest types were 11.2-11.3, 49.0-60.3, and 4.5-5.7, respectively. There was no significant difference in soil C/N among the three stand types. The highest soil C/P and N/P were found in the mixed forest. There was no interaction between soil depth and stand type in affecting soil C, N, P contents and their stoichiometric ratios. There was significant positive correlation between C and N, and between N and C/P in each stand type and soil layer. Soil C/P and N/P had stronger ecological indicating effects on stand types. The coniferous and broad-leaved mixed forest was strongly limited by P availability.

Prediction models and the extrapolation effects for water content of surface dead fuels in the typical stand of the Great Xing'an Mountains of China by one-hour time step.

The water content of surface dead fuels is one of the most important indicators for forecasting fire danger and fire behaviors. We employed the timelag equilibrium water content methods (i.e. Nelson and Simard models) and the meteorological variable regression method to continuously measure the water content of surface dead fuels by one-hour time step from September to October in 2010 under Populus davidiana + Betula platyphylla, Picea koraiensis and the cutover lands (Pinus sylvestris var. mongolica + Betula platyphylla) with different canopy densities in Pangu Forestry Bureau, the Great Xing'an Mountains, Heilongjiang Province, China. We established prediction models and obtained prediction errors. The models were also used to extrapolate the water contents of surface dead fuels under other forest stands and the extrapolation accuracy was analyzed. The results showed that the mean absolute error, the mean relative error and the mean square error root of Nelson model (0.0154, 0.104 and 0.0226) were lower than those of Simard model (0.0185, 0.117 and 0.0256). In terms of extrapolation effects, the mean absolute error, the mean relative error and the mean square error root of meteorological variable regression method (0.0410, 0.0300 and 0.0740) were lower than those of Simard model (0.610, 0.492 and 0.846), but they were higher than those of Nelson model (0.034, 0.021 and 0.0660). Such results indicated that the timelag equilibrium moisture content method by one-hour time step, especially Nelson model, was sui-table for the forest stands in the Great Xing'an Mountains. Although extrapolation could not reduce the prediction errors, it could help improve the prediction accuracy and the efficiency of the present models applied to different forest stands or in a larger scale. The modeling and extrapolation errors were closely related to species identity and canopy densities, thus the appropriate timelag equilibrium moisture content methods should be selected according to different forest stands and locations.

Identification and analysis of the acetylated status of poplar proteins reveals analogous N-terminal protein processing mechanisms with other eukaryotes.

BACKGROUND: The N-terminal protein processing mechanism (NPM) including N-terminal Met excision (NME) and N-terminal acetylation (N(α)-acetylation) represents a common protein co-translational process of some eukaryotes. However, this NPM occurred in woody plants yet remains unknown. METHODOLOGY/PRINCIPAL FINDINGS: To reveal the NPM in poplar, we investigated the N(α)-acetylation status of poplar proteins during dormancy by combining tandem mass spectrometry with TiO2 enrichment of acetylated peptides. We identified 58 N-terminally acetylated (N(α)-acetylated) proteins. Most proteins (47, >81%) are subjected to N(α)-acetylation following the N-terminal removal of Met, indicating that N(α)-acetylation and NME represent a common NPM of poplar proteins. Furthermore, we confirm that poplar shares the analogous NME and N(α)-acetylation (NPM) to other eukaryotes according to analysis of N-terminal features of these acetylated proteins combined with genome-wide identification of the involving methionine aminopeptidases (MAPs) and N-terminal acetyltransferase (Nat) enzymes in poplar. The N(α)-acetylated reactions and the involving enzymes of these poplar proteins are also identified based on those of yeast and human, as well as the subcellular location information of these poplar proteins. CONCLUSIONS/SIGNIFICANCE: This study represents the first extensive investigation of N(α)-acetylation events in woody plants, the results of which will provide useful resources for future unraveling the regulatory mechanisms of N(α)-acetylation of proteins in poplar.