Analysis of the Germplasm Resources and Genetic Relationships Among Hybrid Cymbidium Cultivars and Native Species with RAPD Markers

The random amplified polymorphic DNA （RAPD） marker was assessed to detect the genetic relationships among 48 hybrid Cymbidium cultivars from Japan, Korea, China, and USA, and 2 species of native Cymbidium. Twenty primers were screened from 100 random decamer primers, and a total of 258 DNA bands were amplified, 253 of which （98.1%） were polymorphic. The average number of polymorphic DNA bands amplified by each primer was 12.6. All cultivars were distinguishable when a number of primers were considered. Genetic similarities among the cultivars and species were estimated based on the amount of band sharing ranging from 0.364-0.817 with an average of 0.581. According to the data, a dendrogram of genetic relationship, which was constructed using the UPGMA method, showed that all the tested cultivars and native species were classified into five cluster groups with the similarity coefficient of 0.592. It revealed that the genetic relationships among tested accessions were to some extent related with their origin, flower colour, branch type, and genealogy. It further indicated that the RAPD technique is a useful tool for studying the genetic relationships among hybrid Cymbidium cultivars.

First report of Protokeelia spinifera and Rhopalodia iriomotensis from China,with comments on their systematic positions

Protokeelia is described as a new and rare pennate diatom genus in China. Its valve includes two parts： ventral valve and dorsal valve. The ventral valve is more or less convex or concave. The raphe runs in a distinct elevated and thickened siliceous ridge. In the internal valve, beneath the raphe are fibulae or fibulae clusters which connect the ventral and dorsal valves. One species, P. spinifera Round ＆ Basson, is observed in the water samples from a mangrove forest in Sai Kung, Hong Kong, China. Its main morphological features are described in this paper along with electron microscope （EM） photos. Morphological comparisons are also made among several allied species. In addition, a newly recorded species for China, Rhopalodia iriomotensis Kobayasi, Nagumo ＆ Tanaka, is discussed here. Because several key features observed in this species resemble those of some Protokeelia species, we suggest that it may actually represent a Protokeelia species.

Expression pattern of GASA,downstream genes of DELLA,in Arabidopsis

Separation and functional research of related components involved in gibberellins(GAs) signaling are important to clarify the mechanism of GA functioning.Research on the downstream components of DELLA,the key factor of the GA signaling pathway,is limited at present.GASA(GA-Stimulated in Arabidopsis) family contains 15 genes usually regulated by GA in Arabidopsis thaliana.All GASA proteins have a cleavable signal peptide in N terminus and a conserved GASA domain including 12 cysteines in C terminus.RT-PCR analysis revealed that the expression of GASA4 and GASA6 were down-regulated,but GASA1 and GASA9 were up-regulated in the DELLA mutants,gai-t6 and rga-24,as well as the double mutant,consisting with the results that GASA4 and GASA6 were induced,but GASA1 and GASA9 were inhibited by exogenous GA3.In addition,the expression patterns of other GASA genes were regulated by GA and ABA,separately or cooperatively.Most of GASA genes were expressed in roots,stems,leaves,flowers and developing siliques.GUS gene driven by the promoters of GASA6,GASA7,GASA8,GASA9,GASA10,GASA11 and GASA12 were used as reporters and it was found that all GASA genes expressed in the growing and differentiating organs and abscission zones,suggesting the role of these genes in cell growth and differentiation.This study provided an important basis for functional study of the GASA gene family in the GA and ABA signaling pathway.

Ectopic Expression of FaDREB2 Enhances Osmotic Tolerance in Paper Mulberry

Dehydration-responsive element binding （DREB） proteins are a subfamily of AP2/ERF transcription factors that have been shown to improve tolerance to osmotic stresses in plants. To improve the osmotic stress tolerance of paper mulberry （Broussonetia papyrifera L. Vent）, an economically important tree, we transformed it with a plasmid carrying tall fescue （Festuca arundinacea Schreb） FaDREB2 under the control of CaMV 35S. The ectopic expression of FaDREB2 did not cause growth retardation, and the paper mulberry seedlings expressing FaDREB2 showed higher salt and drought tolerance than wild-type plants （WT）. After 13 d of withholding water, or 15 d in the presence of 250 mM NaCI, all the WT plants died, while the plants expressing FaDREB2 survived. The FaDREB2 transgenic plants had higher leaf water and chlorophyll contents, accumulated more proline and soluble sugars, and had less membrane damage than the WT plants under high salt and water-deficient conditions. Taken together, the results indicate the feasibility of improving tolerance to multiple environmental stresses in paper mulberry seedlings via genetic engineering, by introducing FaDREB2, which promotes the increased accumulation of osmolytes （soluble sugars and proline）, to counter osmotic stresses caused by abiotic factors.

Perturbation of Auxin Homeostasis Caused by Mitochondrial FtSH4 Gene-Mediated Peroxidase Accumulation Regulates Arabidopsis Architecture

Reactive oxygen species and auxin play important roles in the networks that regulate plant development and morphogenetic changes, However, the molecular mechanisms underlying the interactions between them are poorly understood. This study isolated a mas （More Axillary Shoots） mutant, which was identified as an allele of the mitochondrial AAA-protease AtFtSH4, and characterized the function of the FtSH4 gene in regulating plant development by medi- ating the peroxidase-dependent interplay between hydrogen peroxide （H2Oz） and auxin homeostasis. The phenotypes of dwarfism and increased axillary branches observed in the mas （renamed as ftsh4-4） mutant result from a decrease in the IAA concentration. The expression levels of several auxin signaling genes, including IAA1, IAA2, and IAA3, as well as several auxin binding and transport genes, decreased significantly in ftsh4-4 plants. However, the H202 and peroxidases levels, which also have IAA oxidase activity, were significantly elevated in ftsh4-4 plants. The ftsh4-4 phenotypes could be reversed by expressing the iaaM gene or by knocking down the peroxidase genes PRX34 and PRX33. Both approaches can increase auxin levels in the ftsh4-4 mutant. Taken together, these results provided direct molecular and genetic evidence for the interaction between mitochondrial ATP-dependent protease, H2O2, and auxin homeostasis to regulate plant growth and development.

A Putative Chloroplast-Localized Ca2＋/H＋ Antiporter CCHA1 Is Involved in Calcium and pH Homeostasis and Required for PSII Function in Arabidopsis

Calcium is important for chloroplast, not only in its photosynthetic but also nonphotosynthetic functions. Mul- tiple Ca2＋/H＋ transporters and channels have been described and studied in the plasma membrane and organ- elle membranes of plant cells; however, the molecular identity and physiological roles of chloroplast Ca2＋/H＋ antiporters have remained unknown. Here we report the identification and characterization of a member of the UPFO016 family, CCHA1 （a chloroplast-localized potential Ca2＋/H＋ antiporter）, in Arabidopsis thaliana. We observed that the ccha I mutant plants developed pale green leaves and showed severely stunted growth along with impaired photosystem II （PSII） function. CCHA1 localizes to the chloroplasts, and the levels of the PSII core subunits and the oxygen-evolving complex were significantly decreased in the ccha I mutants compared with the wild type. In high Ca2＋ concentrations, Arabidopsis CCHA1 partially rescued the growth defect of yeast gdtl3 null mutant, which is defective in a Ca2＋/H＋ antiporter. The cchal mutant plants also showed significant sensitivity to high concentrations of CaCI2 and MnCI2, as well as variation in pH. Taken these results together, we propose that CCHA 1 might encode a putative chloroplast-localized Ca2＋/H＋ antiporter with critical functions in the regulation of PSII and in chloroplast Ca2＋ and pH homeostasis in Arabidopsis.

SUMO E3 Ligase AtMMS21 Regulates Drought Tolerance in Arabidopsis thaliana

Post-translational modifications of proteins by small ubiquitin-like modifiers （SUMOs） play crucial roles in plant growth and development, and in stress responses. The MMS21 is a newly-identified Arabidopsis thaliana L. SUMO E3 ligase gene aside from the SIZ1, and its function requires further elucidation. Here, we show that MMS21 deficient plants display improved drought tolerance, and constitutive expression of MMS21 reduces drought tolerance. The expression of MMS21 was reduced by abscisic acid （ABA）, polyethylene glycol （PEG） or drought stress. Under drought conditions, mms21 mutants showed the highest survival rate and the slowest water loss, and accumulated a higher level of free proline compared to wild-type （WT） and MMS21 over-expression plants. Stomatal aperture, seed germination and cotyledon greening analysis indicated that mms21 was hypersensitive to ABA. Molecular genetic analysis revealed that MMS21 deficiency led to elevated expression of a series of ABA-mediated stress-responsive genes, including COR15A, RD22, and P5CS1 The ABA and drought-induced stress-responsive genes, including RAB18, RD29A and RD29B, were inhibited by constitutive expression of MMS21. Moreover, ABA-induced accumulation of SUMO-protein conjugates was blocked in the mms21 mutant. We thus conclude that MMS21 plays a role in the drought stress response, likely through regulation of gene expression in an ABA-dependent pathway.

UBC32 Mediated Oxidative Tolerance in Arabidopsis

Extreme environments such as salt stress often increase the reactive oxygen species （ROS） levels （Abogadallah, 2010; Miller et al., 2010）, which cause protein denaturation and damage （Kelsen et al., 2008）. In eukaryotic cells, the endo- plasmic reticulum （ER） lumen is highly oxidative environment, which help newly synthesized proteins form intermolecular or intramolecular disulfide bonds between their cysteine residues. However, the ROS must be regulated according to the folding load to protect the cell from the consequences of oxidative folding.