Significantly improved Escherichia coli tolerance and accumulation of Cd2+, Zn2+ and Cu2+ expressing Streptococcus thermophilus StGCS-GS with high glutathione content

Streptococcus thermophilus γ-glutamylcysteine synthetase-glutathione synthetase (StGCS-GS) which synthesized glutathione (GSH) without limit feedback inhibition was over-expressed as a fusion protein of TrxA-StGCS-GS to analyze its possibly functional role in heavy metal tolerance of Escherichia coli (BL21). For comparative analyses, Arabidopsis γ-glutamylcysteine synthetase (AtGCS) and glutathione synthetase (AtGS) were introduced into Escherichia coli (E. coli) in the same manner, respectively. The results showed that the growth and survivability of E. coli over-expressing TrxA-StGCS-GS were slightly influenced by 1 mM Cd²⁺, Zn²⁺ and Cu²⁺ toxicity, and it could withstand duration of these heavy metal stresses competently. In contrast, the two strains over-expressing TrxA-AtGCS and TrxA-AtGS were impacted apparently; the BL21 empty strain was even almost suppressed. Meanwhile, a much higher bioaccumulation of Cd²⁺, Zn²⁺, Cu²⁺ ions and glutathione content were observed in the strain over-expressing TrxA-StGCS-GS than in the other comparison strains. It could be concluded that over-expression of StGCS-GS offered a more significant enhancement of heavy metal tolerance to E. coli with superior GSH content to accumulate considerable heavy metal.     

Development of nutritious rice with high zinc/selenium and low cadmium in grains through QTL pyramiding

Enriching zinc (Zn) and selenium (Se) levels, while reducing cadmium (Cd) concentration in rice grains is of great benefit for human diet and health. Large natural variations in grain Zn, Se, and Cd concentrations in different rice accessions enable Zn/Se‐biofortification and Cd‐minimization through molecular breeding. Here, we report the development of new elite varieties by pyramiding major quantitative trait loci (QTLs) that significantly contribute to high Zn/Se and low Cd accumulation in grains. A chromosome segment substitution line CSSL^GCC7 with the PA64s‐derived GCC7 allele in the 93‐11 background, exhibited steadily higher Mn and lower Cd concentrations in grains than those of 93‐11. This elite chromosome segment substitution line (CSSL) was used as the core breeding material to cross with CSSLs harboring other major QTLs for essential mineral elements, especially CSSL^GZC6 for grain Zn concentration and CSSL^GSC5 for grain Se concentration. The CSSL^GCC7+GZC6 and CSSL^GCC7+GSC5 exhibited lower Cd concentration with higher Zn and Se concentrations in grains, respectively. Our study thus provides elite materials for rice breeding targeting high Zn/Se and low Cd concentrations in grains.     

Map-based cloning proves qGC-6, a major QTL for gel consistency of japonica/indica cross, responds by Waxy in rice (Oryza sativa L.)

In this study, one major QTL affecting gel consistency (GC) of japonica/indica cross was identified on chromosome 6 using a DH population. To understand the molecular mechanism that regulates GC in rice grains, the major QTL (qGC-6) was isolated through a map-based cloning approach utilizing chromosome segment substitution lines (CSSLs). Using 64 plants with extremely soft GC that were selected on recombinant break points between two SSR markers, RM540 and RM8200 in a BC4F2 population, qGC-6 was mapped to a 60-kb DNA region between two STS markers, S26 and S27. These two markers were then used to further identify recombination break points. Finally, qGC-6 was delimited in an interval of a 11-kb region. Gene prediction analysis of the 11-kb DNA sequence containing qGC-6 identified only one putative ORF, which encodes granule-bound starch synthesis protein (Wx protein). Results of sequencing analysis and complementation experiment confirmed that this candidate ORF is responsible for rice GC. Genetic evidences revealed that Wx might contribute equally to the grain amylose content-controlling gene as well as gel consistency. This new information is important to breed rice varieties with improved grain quality.     

EARLY SENESCENCE1 Encodes a SCAR-LIKE PROTEIN2 That Affects Water Loss in Rice

The global problem of drought threatens agricultural production and constrains the development of sustainable agricultural practices. In plants, excessive water loss causes drought stress and induces early senescence. In this study, we isolated a rice (Oryza sativa) mutant, designated as early senescence1 (es1), which exhibits early leaf senescence. The es1-1 leaves undergo water loss at the seedling stage (as reflected by whitening of the leaf margin and wilting) and display early senescence at the three-leaf stage. We used map-based cloning to identify ES1, which encodes a SCAR-LIKE PROTEIN2, a component of the suppressor of cAMP receptor/Wiskott-Aldrich syndrome protein family verprolin-homologous complex involved in actin polymerization and function. The es1-1 mutants exhibited significantly higher stomatal density. This resulted in excessive water loss and accelerated water flow in es1-1, also enhancing the water absorption capacity of the roots and the water transport capacity of the stems as well as promoting the in vivo enrichment of metal ions cotransported with water. The expression of ES1 is higher in the leaves and leaf sheaths than in other tissues, consistent with its role in controlling water loss from leaves. GREEN FLUORESCENT PROTEIN-ES1 fusion proteins were ubiquitously distributed in the cytoplasm of plant cells. Collectively, our data suggest that ES1 is important for regulating water loss in rice.Rice (Oryza sativa) is a major worldwide food crop, but it consumes more water than most crops (Linquist et al., 2015), with water consumption for rice cultivation accounting for approximately 65% of agricultural water usage. Rice provides a staple food for about 3 billion people while using an estimated 24% to 30% of the world’s developed freshwater resources (Bouman et al., 2007). Severe water shortages restrict the expansion of rice production and hinder the irrigation of existing paddy fields (Zhu and Xiong, 2013). One effective way to overcome water shortages is to reduce water loss in rice plants, thus allowing the cultivation of this key crop in environments with less water (Nguyen et al., 1997).In plants, the stomata on the leaf surface work as the main channels for the discharge of water and the entry of carbon dioxide, thus strongly affecting physiological processes such as transpiration and photosynthesis. Previous studies showed that mutations in some genes could affect stomatal density or differentiation, such as the Arabidopsis (Arabidopsis thaliana) genes TOO MANY MOUTHS (AtTMM; Yang and Sack, 1995), SCREAM2 (SCRM2; Kanaoka et al., 2008), STOMATA DENSITY AND DISTRIBUTION1 (AtSDD1; Von Groll et al., 2002), and AtYODA2, a mitogen-activated protein kinase kinase kinase (Bergmann et al., 2004). Stomata show a regular distribution on rice leaves (Huang et al., 2009) during plant growth and development, and various environmental factors affect the density and size of stomata as well as the chlorophyll contents of rice leaves. For example, rice leaves that develop under water stress show substantially fewer stomata compared with leaves that develop under well-watered conditions (Huang et al., 2009). Changes in stomatal density and morphology affect water loss (Boonrueng et al., 2013). In rice, SIMILAR TO RADICAL-INDUCED CELL DEATH1 enhances drought tolerance by regulating stomatal closure (You et al., 2013), while the zinc finger protein DROUGHT AND SALT TOLERANCE functions in drought and salt tolerance by adjusting stomatal aperture (Huang et al., 2009). In Arabidopsis, overexpression of the magnesium chelatase H subunit in guard cells confers drought tolerance by promoting stomatal closure (Tsuzuki et al., 2013). Thus, stomatal closure and low stomatal density enhance drought tolerance by reducing water loss in plants.The epicuticular wax layer in plants acts as the first barrier to environmental conditions by reducing water loss due to transpiration and preventing plant damage due to excessively strong sunlight (Riederer and Schreiber, 2001). Leaf transpiration involves both stomatal and cuticular transpiration. Stomatal conductance controls stomatal transpiration, but the physicochemical properties of the leaf surface mainly control cuticular transpiration. For example, the composition, thickness, and microstructure of the cuticular wax affect water permeability and transport (Svenningsson, 1988; Xu et al., 1995; Buschhaus and Jetter, 2012). Rice DROUGHT-INDUCED WAX ACCUMULATION1, GLOSSY1, and WAX SYNTHESIS REGULATORY GENE1 affect drought tolerance by regulating the deposition or biosynthesis of cuticular wax (Islam et al., 2009; Wang et al., 2012; Zhou et al., 2013; Zhu and Xiong, 2013).Besides, leaf trichomes can also affect water loss (Konrad et al., 2015) and leaf trichomes closely linked with the actin cytoskeleton. The involvement of the actin cytoskeleton in controlling directional cell expansion in trichomes has received much attention (Zhang et al., 2005). Generally, genes that affect cytoplasmic organization can be studied by screening leaf trichome mutants (Qiu et al., 2002). In Arabidopsis, a reproducible morphogenetic program directs the polarized development of trichome branches (Mathur et al., 1999; Szymanski et al., 1999; Le et al., 2006). Some of these genes affect the cytoskeleton and also affect the morphology of normal plant cells, especially epidermal cells. For example, mutation of SPIKE1 in Arabidopsis causes epidermal cells to show simple arrangements and morphologies (i.e. all cells dividing along a single axis; Qiu et al., 2002).To study the molecular mechanisms underlying water loss in rice, we isolated and characterized the early senescence1-1 (es1-1) rice mutant, which showed excessive water loss and early senescence phenotypes. Map-based cloning data showed that ES1 encodes a SCAR-LIKE PROTEIN2, and its Arabidopsis homolog affects the polymerization of actin. The es1-1 mutants showed obvious changes in leaf trichomes, similar to Arabidopsis. However, few studies have reported a connection between the actin cytoskeleton and water loss in Arabidopsis. Our results demonstrated a critical role of the actin cytoskeleton in regulating water loss in rice.     

The pleiotropic ABNORMAL FLOWER AND DWARF1 affects plant height,floral development and grain yield in rice

Moderate plant height and successful establishment of reproductive organs play pivotal roles in rice grain production. The molecular mechanism that controls the two aspects remains unclear in rice. In the present study, we characterized a rice gene, ABNORMAL FLOWER AND DWARF1 (AFD1) that determined plant height, floral development and grain yield. The afd1 mutant showed variable defects including the dwarfism, long panicle, low seed setting and reduced grain yield. In addition, abnormal floral organs were also observed in the afd1 mutant including slender and thick hulls, and hull‐like lodicules. AFD1 encoded a DUF640 domain protein and was expressed in all tested tissues and organs. Subcellular localization showed AFD1‐green fluorescent fusion protein (GFP) was localized in the nucleus. Meantime, our results suggested that AFD1 regulated the expression of cell division and expansion related genes.     

温度与聚群对三种仔兽热能代谢的影响

仔兽出生以前,是在相对稳定而安全的母兽子宫内生活的,出生以后,仔兽的营养条件与环境温度即起了根本的变化。新生仔兽是如何适应新环境的?仔兽在新环境中的生活能力怎样?环境温度与食物条件对新生仔兽的存活率、生长与发育的影响如何?环境温度和聚群行为与能量代谢的关系怎样?这是一系列的基础理论问题,尤其是毛皮动物饲养业所关心的实际问题。