Qiang Wei

Ectopic expression of an Ammopiptanthus mongolicus H+-pyrophosphatase gene enhances drought and salt tolerance in Arabidopsis

An orthologue of the vacuolar H+-pyrophosphatase (H+-PPase) gene, AmVP1, was isolated from a desert plant, Ammopiptanthus mongolicus (Leguminosae), by RACE-PCR. AmVP1 has a total length of 2,875xa0bp, with an open reading frame of 2,316xa0bp, which encodes a predicted polypeptide of 771 amino acids. Sequence analysis revealed that it has high similarity with the VP1 proteins from other plants. AmVP1 was strongly induced by drought stress, but only responded initially to a salt stress. In addition, a 1.8xa0kb upstream sequence of AmVP1 was isolated from the genomic DNA of A. mongolicus by TAIL-PCR. Cis-element as well as promoter prediction analysis indicated that it contained three promoter sequences and more than 50 cis-elements. Heterologous expression of AmVP1 in the yeast mutant ena1 could partially suppress its hypersensitivity to NaCl. Over-expressing AmVP1 resulted in enhanced tolerances to both drought and salt stresses in transgenic Arabidopsis plants. The transgenic plants accumulated more sodium and potassium in their leaves after salt stress, and retained more water while producing less malondialdehyde during drought stress. A comparative study of salt tolerance between AtVP1 (an H+-PPase from Arabidopsis) and AmVP1 transgenic Arabidopsis suggested that the efficiency of AmVP1 is more than threefold higher than AtVP1. Our work suggested that AmVP1 functioned as a typical VP1 gene, but might be a more efficient orthologue than AtVP1 and therefore a valuable gene for improving plant salt and drought tolerances.

Exploring key cellular processes and candidate genes regulating the primary thickening growth of Moso underground shoots.

The primary thickening growth of Moso (Phyllostachys edulis) underground shoots largely determines the culm circumference. However, its developmental mechanisms remain largely unknown. Using an integrated anatomy, mathematics and genomics approach, we systematically studied cellular and molecular mechanisms underlying the growth of Moso underground shoots. We discovered that the growth displayed a spiral pattern and pith played an important role in promoting the primary thickening process of Moso underground shoots and driving the evolution of culms with different sizes among different bamboo species. Different with model plants, the shoot apical meristem (SAM) of Moso is composed of six layers of cells. Comparative transcriptome analysis identified a large number of genes related to the vascular tissue formation that were significantly upregulated in a thick wall variant with narrow pith cavity, mildly spiral growth, and flat and enlarged SAM, including those related to plant hormones and those involved in cell wall development. These results provide a systematic perspective on the primary thickening growth of Moso underground shoots, and support a plausible mechanism resulting in the narrow pith cavity, weak spiral growth but increased vascular bundle of the thick wall Moso.

Establishment of an efficient micropropagation and callus regeneration system from the axillary buds of Bambusa ventricosa

Based on the screening of various hormone combinations, we have established an efficient micropropagation and callus regeneration system from the axillary buds of B. ventricosa. We found that 6-benzyladenine (6-BA) had a dominant role in promoting bud sprouting, multiple bud induction and proliferation in B. ventricosa. Meanwhile α-naphthaleneacetic acid (NAA) was found to be an effective factor of inducing rooting in proliferated buds. The Murashige and Skoog medium containing 22.2xa0µM 6-BA was optimal for bud initiation, and the MS medium containing 26.6xa0µM 6-BA provided a good result for multiple bud induction. However, for buds proliferation MS medium containing 22.2xa0µM 6-BA, 0.23xa0µM Thidiazuron (TDZ: N-phenyl-N-[(1, 2, 3-thidiazol-5-yl) urea]) and 0.27xa0µM NAA was found to be very effective. The optimal medium for rooting of proliferated bud was MS medium containing 2.7xa0µM NAA, 4.9xa0µM indole butyric acid and 4.4xa0µM 6-BA. Based on the establishment of an efficient micropropagation system, we investigated the frequencies of callus formation from buds of in virto raised plantlets under different culture conditions. We showed that media containing 27xa0µM 2, 4-dichlorophenoxyacetic acid (2, 4-D), 2.7xa0µM NAA and 0.0045xa0µM TDZ effectively produced callus. The callus induction rate varied between it to 60 percent. TDZ was found to be a main factor influencing the callogenesis of B. ventricosa. Medium containing 22.6xa0µM 2, 4-D, 2.2xa0µM 6-BA and 5.4xa0µM NAA was preferred for callus amplification among the four tested subculture media. Plants were successfully regenerated on a MS medium containing 13.3xa0µM 6-BA and 2.7xa0µM NAA, subsequently acclimatized and transplanted to an experimental pod.

Ectopic-overexpression of an HD-Zip IV transcription factor from Ammopiptanthus mongolicus (Leguminosae) promoted upward leaf curvature and non-dehiscent anthers in Arabidopsis thaliana

Several HD-ZIP IV transcription factors have been reported to play important roles in plant growth and development. However, the functions of most members remain unknown. In this study, an HD-ZIP IV transcription factor, AmHDG1, was identified from desert shrub Ammopiptanthus mongolicus (Leguminosae) by RACE PCR. AmHDG1 consists of 2,508xa0bp, has an open reading frame of 2,292xa0bp, and encodes a predicted polypeptide of 763 amino acids. Phylogenic analysis with the HD-ZIP IV transcription factor family of Arabidopsis showed that it is clustered with the subfamily of AtHDG1 and AtANL2. AmHDG1 is localized in the nucleus and is able to activate transcription in yeast. In A. mongolicus, AmHDG1 is preferentially expressed in young leaves. Constitutive overexpression of AmHDG1 results in upcurved leaves and non-dehiscent anthers in Arabidopsis thaliana. In the flowers of AmHDG1 overexpressors, the expression levels of two positive regulators of anther dehiscence, AtNST1 and AtNST2, are down-regulated. On the other hand, the transcript level of another positive regulator, AtMYB26 is not influenced. Taken together, our data demonstrate that AmHDG1 plays a negative role in the regulation of anther dehiscence.

Identification of an AtCRN1-like chloroplast protein BeCRN1 and its distinctive role in chlorophyll breakdown during leaf senescence in bamboo ( Bambusa emeiensis ‘ Viridiflavus ’)

CRN1/PPH/NYC3 is one of the key genes responsible for chlorophyll degradation during senescence in both Arabidopsis and rice. In this study, BeCRN1 and its promoter, BeCRN1p, were isolated from, Bambusa emeiensis ‘Viridiflavus’, a bamboo variety, for the first time. BeCRN1 consists of 1,646xa0bp, with an open reading frame of 1,473xa0bp, encoding a predicted polypeptide of 490 amino acids. Besides, BeCRN1 contained 5 exons and 4 introns, and harbored a distinctive microsatellite in the fourth intron. Differences in BeCRN1p are observed primarily in the AtCRN1 promoter, while sharing similar cis element composition with the rice CRN1 promoter. BeCRN1 is localized within the chloroplast, and it is strongly induced by senescence signals. Although constitutive overexpression of BeCRN1 in crn1 has reversed the stay-green phenotype of crn1 to the wild type phenotype, its promoter has failed to do so with AtCRN1 following dark treatment. The efficiency of BeCRN1p is only about one-third of that of the AtCRN1 promoter.

Why Does Not the Leaf Weight-Area Allometry of Bamboos Follow the 3/2-Power Law?

The principle of similarity (Thompson, 1917) states that the weight of an organism follows the 3/2-power law of its surface area and is proportional to its volume on the condition that the density is constant. However, the allometric relationship between leaf weight and leaf area has been reported to greatly deviate from the 3/2-power law, with the irregularity of leaf density largely ignored for explaining this deviation. Here, we choose 11 bamboo species to explore the allometric relationships among leaf area (A), density (ρ), length (L), thickness (T), and weight (W). Because the edge of a bamboo leaf follows a simplified two-parameter Gielis equation, we could show that A ∝ L2 and that A ∝ T2. This then allowed us to derive the density-thickness allometry ρ ∝ Tb and the weight-area allometry W ∝ A(b+3)/2 ≈ A9/8, where b approximates −3/4. Leaf density is strikingly negatively associated with leaf thickness, and it is this inverse relationship that results in the weight-area allometry to deviate from the 3/2-power law. In conclusion, although plants are prone to invest less dry mass and thus produce thinner leaves when the leaf area is sufficient for photosynthesis, such leaf thinning needs to be accompanied with elevated density to ensure structural stability. The findings provide the insights on the evolutionary clue about the biomass investment and output of photosynthetic organs of plants. Because of the importance of leaves, plants could have enhanced the ratio of dry material per unit area of leaf in order to increase the efficiency of photosynthesis, relative the other parts of plants. Although the conclusion is drawn only based on 11 bamboo species, it should also be applicable to the other plants, especially considering previous works on the exponent of the weight-area relationship being less than 3/2 in plants.

Cellular and molecular characterizations of a slow-growth variant provide insights into the fast growth of bamboo.

Few studies about bamboo naturally occurring mutants have been reported so far. Using an integrated anatomy, mathematics and genomics approach, we systematically characterized the cellular and molecular basis underlying the abnormal internode development of Pseudosasa japonica var. tsutsumiana, a stable variant with dwarf and swollen internodes that are caused by the compressed spiral growth and the swollen cells in the bottom part of the internode. P. japonica var. tsutsumiana is a slow-growth variant with disorderly cell division and cell growth during the fast growth stage. Comparative transcriptome analysis identified a number of genes related to cell growth that were significantly down-regulated in the variant, including those related to auxin, vesicle transport, cytoskeleton organization and cell wall modification, consistent with the thinner cell walls and lower contents of cellulose that were found in the variant, which together with the mechanic force composed by the extrusion pressure from the neighboring fast growth cells and the weight pressure above the growing cells might finally result in the radial and irregular growth of the variant cells. This study provides key candidate genes involved in the fast growth of bamboo from a mutant perspective, and supports a plausible mechanism underlying the dwarf and swollen internodes of P. japonica var. tsutsumiana.

Molecular cloning and characterization of a chlorophyll degradation regulatory gene from bamboo

Leaf senescence constituted the final stage of leaf development and it is always accompanied by the leaf yellowing. The non-yellowing gene (NYE1), initially identified from Arabidopsis in our laboratory, is a key regulatory gene responsible for chlorophyll degradation during senescence. In this study, an orthologue of AtNYE1 was isolated from the bamboo (Bambusa emeiensis cv. Viridiflavus) and tentatively named BeNYE1. The full length sequence of 1 386 bp contains an open reading frame of 801 bp. The protein encoded by BeNYE1 consists of 266 amino acids. Sequence analysis revealed that BeNYE1 had high similarity with other NYE/SGR proteins from various monocotyledon species. BeNYE1 was strongly induced by natural senescence and dark-induced senescence in bamboo. Driven by a 1.5 kb upstream fragment of AtNYE1, BeNYE1 could rescue the stay-green phenotype of nye1-1. The constitutive over-expression of BeNYE1 could accelerate the chlorophyll degradation. These results indicated that BeNYE1 might play an important role in the regulation of chlorophyll degradation during leaf senescence in bamboo.