Jasmonate-Sensitivity-Assisted Screening and Characterization of Nicotine Synthetic Mutants from Activation-Tagged Population of Tobacco (Nicotiana tabacum L.).

Nicotine is a secondary metabolite that is important to the defense system and commercial quality of tobacco (Nicotiana tabacum L.). Jasmonate and its derivatives (JAs) are phytohormone regulators of nicotine formation; however, the underlying molecular mechanism of this process remains largely unclear. Owing to the amphitetraploid origin of N. tabacum, research on screening and identification of nicotine-synthetic mutants is relatively scarce. Here, we describe a method based on JA-sensitivity for screening nicotine mutants from an activation-tagged population of tobacco. In this approach, the mutants were first screened for abnormal JA responses in seed germination and root elongation, and then the levels of nicotine synthesis and expression of nicotine synthetic genes in the mutants with altered JA-response were measured to determine the nicotine-synthetic mutants. We successfully obtained five mutants that maintained stable nicotine contents and JA responses for three generations. This method is simple, effective and low-cost, and the finding of transcriptional changes of nicotine synthetic genes in the mutants shows potentials for identifying novel regulators involved in JA-regulated nicotine biosynthesis.

The complete chloroplast genome sequence of Schefflera octophylla.

The complete chloroplast genome sequence of Schefflera octophylla, a critical Chinese medicine was reported here. The complete chloroplast genome of Schefflera octophylla is 156 685 bp in length with 37.93% overall GC content. A pair of IRs (inverted repeats) of 25 965 bp were separated by LSC (86 609 bp) and SSC (18 146 bp). The phylogenetic analysis of 17 taxa showed a strong sister relationship with Schefflera delavayi. Furthermore the Araliaceae was separated into two major groups.

Exploring the best model for describing light-response curves in two Epimedium species.

Photosynthetic responses to light environment can be useful measurements to determine favorable habitat conditions for the conservation and cultivation of medicinal species. The nonrectangular hyperbola model, rectangular hyperbola model, modified rectangular hyperbola model, exponential model, modified exponential model are used to explore the best model for describing light-response curves in two Epimedium species. The results show that the light-response curves of E. wushanense and E. acuminatum were best described by the modified exponential model, the test MSE and MAE of the modified exponential model were smaller, and the LSP and Pmax calculated by the modified exponential model were more accurate than those calculated by other models in E. wushanense and E. acuminatum. This model may be widely applicable to light-response curves of other Epimedium species.

Seasonal dynamics of mobile carbon supply in Quercus aquifolioides at the upper elevational limit.

Many studies have tried to explain the physiological mechanisms of the alpine treeline phenomenon, but the debate on the alpine treeline formation remains controversial due to opposite results from different studies. The present study explored the carbon-physiology of an alpine shrub species (Quercus aquifolioides) grown at its upper elevational limit compared to lower elevations, to test whether the elevational limit of alpine shrubs (<3 m in height) are determined by carbon limitation or growth limitation. We studied the seasonal variations in non-structural carbohydrate (NSC) and its pool size in Q. aquifolioides grown at 3000 m, 3500 m, and at its elevational limit of 3950 m above sea level (a.s.l.) on Zheduo Mt., SW China. The tissue NSC concentrations along the elevational gradient varied significantly with season, reflecting the season-dependent carbon balance. The NSC levels in tissues were lowest at the beginning of the growing season, indicating that plants used the winter reserve storage for re-growth in the early spring. During the growing season, plants grown at the elevational limit did not show lower NSC concentrations compared to plants at lower elevations, but during the winter season, storage tissues, especially roots, had significantly lower NSC concentrations in plants at the elevational limit compared to lower elevations. The present results suggest the significance of winter reserve in storage tissues, which may determine the winter survival and early-spring re-growth of Q. aquifolioides shrubs at high elevation, leading to the formation of the uppermost distribution limit. This result is consistent with a recent hypothesis for the alpine treeline formation.

Nitrogen and carbon source-sink relationships in trees at the Himalayan treelines compared with lower elevations.

No single hypothesis or theory has been widely accepted for explaining the functional mechanism of global alpine/arctic treeline formation. The present study tested whether the alpine treeline is determined by (1) the needle nitrogen content associated with photosynthesis (carbon gain); (2) a sufficient source-sink ratio of carbon; or (3) a sufficient C-N ratio. Nitrogen does not limit the growth and development of trees studied at the Himalayan treelines. Levels of non-structural carbohydrates (NSC) in trees were species-specific and site-dependent; therefore, the treeline cases studied did not show consistent evidence of source/carbon limitation or sink/growth limitation in treeline trees. However, results of the combined three treelines showed that the treeline trees may suffer from a winter carbon shortage. The source capacity and the sink capacity of a tree influence its tissue NSC concentrations and the carbon balance; therefore, we suggest that the persistence and development of treeline trees in a harsh alpine environment may require a minimum level of the total NSC concentration, a sufficiently high sugar:starch ratio, and a balanced carbon source-sink relationship.

Mobile carbohydrates in Himalayan treeline trees I. Evidence for carbon gain limitation but not for growth limitation.

To test whether the altitudinal distribution of trees is determined by a carbon shortage or an insufficient sugar fraction (sugar:starch ratio) in treeline trees, we studied the status of nonstructural carbohydrates (NSC) and their components (total soluble sugars and starch) in Abies fabri (Mast.) Craib and Picea balfouriana var. hirtella Rehd. et Wils. trees along three elevational gradients, ranging from lower elevations to the alpine treeline, on the eastern edge of the Tibetan Plateau. For comparison, we investigated a low-altitude species (Tsuga yunnanensis (Franch.) Pritz.) which served as a warm-climate reference because it is distributed in closed montane forests below 3100 m a.s.l. in the study area. The carbon status of T. yunnanensis responded to altitude differently from that of the treeline species. At the species level, total NSC was not consistently more abundant in treeline trees than in trees of the same species growing at lower elevations. Thus there was no consistent evidence for carbon limitation of growth in treeline trees. For the three treeline species studied (P. balfouriana and A. fabri in the Kang-Ding Valley and A. fabri in the Mo-Xi Valley), winter NSC concentrations in treeline trees were significantly lower than in lower-elevation trees of the same species, suggesting that, in winter, carbon is limited in treeline trees. However, in no case was there total overwinter depletion of NSC or its components in treeline trees. Treeline and low-altitude species had similar sugar:starch ratios of about three at their upper-elevational limits in April. We conclude that survival and growth of trees at the elevational or latitudinal climate limit depend not only on NSC concentration in perennial tissues, but also on the maintenance of an overwintering sugar:starch ratio greater than three.

[Altitudinal changes in leaf mass per unit area and tissue non-structural carbohydrates content of Abies fabri on Gongga Mountain of southwest China].

Taking the northeast slope of Moxi vally and southwest slope of Kangding vally in Gongga Mountain of Southwest China as sampling sites, this paper investigated the leaf mass per unit area (LMA) and tissue non-structural carbohydrates content (NSC) of Abies fabri distributed at the positions from lower elevations to alpine treeline during the periods of dormancy and vigorous growth. The results indicated that A. fabri had higher LMA and NSC in warm-moist Moxi valley than in hot-dry Kangding valley. The LMA and NSC of treeline trees were all higher than those of the trees at lower elevations, which was more obvious during the period of vigorous growth. The overall altitudinal changing trends of LMA and NSC in Gongga Mountain of Southwest China did not support the hypothesis of 'carbon limitation could induce the formation of alpine treeline'.

Molecular cloning and characterization of a mannose-binding lectin gene from Crinum asiaticum.

Full-length cDNA of a mannose-binding lectin or agglutinin gene was cloned from a traditional Chinese medicinal herb Crinum asiaticum var. sinicum through RACE-PCR cloning. The full-length cDNA of C. asiaticum agglutinin (caa) was 820 bp and contained a 528 bp open reading frame encoding a lectin precursor (preproprotein) of 175 amino acid residues with a 22 aa signal peptide. The coding region of the caa gene was high in G/C content. The first 20 bp of the 5' UTR had a dC content of 50%, which was a typical feature of the leader sequence. By cutting away the signal peptide, the CAA proprotein was 15.79 kDa with a pl of 9.27 and contained 3 mannose-binding sites (QDNY). Random coil and extended strand constituted interlaced domination of the main part of the secondary structure. B-lectin conserved domain existed within N24 to G130. Predicted three-dimensional structure of CAA proprotein was very similar to that of GNA (Galanthus nivalis agglutinin). It is significant that besides certain homologies to known monocot mannose-binding lectins from Amaryllidaceae, Orchidaceae, Alliaceae and Liliaceae, caa also showed high similarity to gastrodianin type antifungal proteins. No intron was detected within the region of genomic sequence corresponding to the caa full-length cDNA. Southern blot analysis indicated that the caa gene belonged to a low-copy gene family. Northern blot analysis demonstrated that caa mRNA was constitutively expressed in all the tested tissue types including the root, bulb, leaf, rachise, flower and fruit tissues.

Molecular cloning of a potential Verticillium dahliae resistance gene SlVe1 with multi-site polyadenylation from Solanum licopersicoides.

Caused by Verticillium spp. pathogens, verticillium wilt is a common detrimental disease damaging yield production of many important crops. Isolation of verticillium wilt resistance genes and their transgenic application is a fundamental way to control this disease. Here we report the cloning and sequence characterization of a potential Verticillium dahliae Kleb. resistance gene (Ve) from Solanum lycopersicoides Dun. (designated as SlVe1). The nucleotide sequence of SlVe1 is 3400 bp with an ORF of 3156 bp encoding a protein precursor of 1051 amino acids (aa). Unlike tomato Ve1, SlVe1 had a short leader sequence of 22 bp. Multiple polyadenylation sites were detected, which may result from alternative cleavages directed by the common polyadenylation signal AATAAA, and nucleotide sequences of the cleavage sites for polyadenylation conform to PyPyA. Sharing high homologies to tomato verticillium wilt disease resistance genes Ve1 and Ve2, SlVe1 encoded a cell-surface glycoprotein with receptor-mediated endocytosis-like signal. The leucine rich (16.51%) putative SlVe1 protein had a calculated molecular weight of 116.97 kDa with an isoelectric point of 5.22. It possessed a hydrophobic N-terminal signal peptide of 23 aa and 28 predicted significant leucine-rich repeats (LRRs) containing 29 potential N-glycosylation sites (18 being significant). A membrane-associated hydrophobic domain resided within the C-terminal, flanked by a neutral/acidic aa rich domain and a neutral/basic aa rich domain. Forty-four predicted phosphorylation sites (28 for S, 5 for T and 11 for Y) distributed in SlVe1, and an endocytosis signal EKWLLW resided in the neutral/basic aa rich C-terminal domain. As compared with Ve1, several clues of variations have been detected in SlVe1 and their possible implications are discussed.