Seedling Traits Determine Drought Tolerance of Tropical Tree Species

Water availability is the most important factor determining tree species distribution in the tropics, but the underlying mechanisms are still not clear. In this study, we compared functional traits of 38 tropical tree species from dry and moist forest, and quantified their ability to survive drought in a dry‐down experiment in which wilting and survival were monitored. We evaluated how seedling traits affect drought survival, and how drought survival determines species distribution along the rainfall gradient. Dry forest species tended to have compound leaves, high stem dry matter content (stem dry mass/fresh mass), and low leaf area ratio, suggesting that reduction of transpiration and avoidance of xylem cavitation are important for their success. Three functional groups were identified based on the seedling traits: (1) drought avoiders with a deciduous leaf habitat and taproots; (2) drought resisters with tough tissues (i.e., a high dry matter content); and (3) light‐demanding moist forest species with a large belowground foraging capacity. Dry forest species had a longer drought survival time (62 d) than moist forest species (25 d). Deciduousness explained 69 percent of interspecific variation in drought survival. Among evergreen species, stem density explained 20 percent of the drought survival. Drought survival was not related to species distribution along the rainfall gradient, because it was mainly determined by deciduousness, and species with deciduous seedlings are found in both dry and moist forests. Among evergreen species, drought survival explained 28 percent of the variation in species position along the rainfall gradient. This suggests that, apart from drought tolerance, other factors such as history, dispersal limitation, shade tolerance, and fire shape species distribution patterns along the rainfall gradient.     

Characterization of Biocontrol Traits in Heterorhabditis floridensis: A Species with Broad Temperature Tolerance

Biological characteristics of two strains of the entomopathogenic nematode, Heterorhabditis floridensis (332 isolated in Florida and K22 isolated in Georgia) were described. The identity of the nematode’s symbiotic bacteria was elucidated and found to be Photorhabdus luminescens subsp. luminescens. Beneficial traits pertinent to biocontrol (environmental tolerance and virulence) were characterized. The range of temperature tolerance in the H. floridensis strains was broad and showed a high level of heat tolerance. The H. floridensis strains caused higher mortality or infection in G. mellonella at 30°C and 35°C compared with S. riobrave (355), a strain widely known to be heat tolerant, and the H. floridensis strains were also capable of infecting at 17°C whereas S. riobrave (355) was not. However, at higher temperatures (37°C and 39°C), though H. floridensis readily infected G. mellonella, S. riobrave strains caused higher levels of mortality. Desiccation tolerance in H. floridensis was similar to Heterorhabditis indica (Hom1) and S. riobrave (355) and superior to S. feltiae (SN). H. bacteriophora (Oswego) and S. carpocapsae (All) exhibited higher desiccation tolerance than the H. floridensis strains. The virulence of H. floridensis to four insect pests (Aethina tumida, Conotrachelus nenuphar, Diaprepes abbreviatus, and Tenebrio molitor) was determined relative to seven other nematodes: H. bacteriophora (Oswego), H. indica (Hom1), S. carpocapsae (All), S. feltiae (SN), S. glaseri (4-8 and Vs strains), and S. riobrave (355). Virulence to A. tumida was similar among the H. floridensis strains and other nematodes except S. glaseri (Vs), S. feltiae, and S. riobrave failed to cause higher mortality than the control. Only H. bacteriophora, H. indica, S. feltiae, S. riobrave, and S. glaseri (4-8) caused higher mortality than the control in C. nenuphar. All nematodes were pathogenic to D. abbreviatus though S. glaseri (4-8) and S. riobrave (355) were the most virulent. S. carpocapsae was the most virulent to T. molitor. In summary, the H. floridensis strains possess a wide niche breadth in temperature tolerance and have virulence and desiccation levels that are similar to a number of other entomopathogenic nematodes. The strains may be useful for biocontrol purposes in environments where temperature extremes occur within short durations.     

Comparative Physiology and Growth of Two Perennial Tussock Grass Species in a Semi-Arid Environment

The physiology and growth ofLygeum spartumandStipa tenacissima,two perennial tussock grasses which dominate wide areas of semi-aridsouth-eastern Spain, were compared at times of high and lowavailability of water, in autumn and summer respectively, tostudy the adaptation of this growth form to arid environments.The two species differed in morphological and physiologicaltraits.Stipatussocks were larger and had opportunistic growth,andStipaleaves had a smaller specific area and lower diffusiveconductance to water vapour. The two grasses were similar inmaximum photosynthetic rate, leaf nitrogen concentration, andin the response to high light conditions but had different tissuewater relations.Stipawas better suited to cope with droughtand erratic rainfall, because of its more effective controlof water loss and its growth patterns.Lygeumseems to be adaptedto less dry conditions and more saline soils. The tussock growthform provides an adaptive advantage in these infertile environmentsby reducing radiation absorbance. leaf extension; Lygeum spartum; perennial grassland; semi-arid environments; Stipa tenacissima; tussock grass; water relations; Adaptation; growth; photosynthesis     

Differential Drought Responses in F-box Gene Expression and Grain Yield Between Two Rice Groups with Contrasting Drought Tolerance

Understanding the molecular mechanisms regulating rice’s response to drought stress is important for cereal crop development. We investigated the physiological and gene expression responses of three drought-tolerant and two drought-sensitive unrelated rice cultivars at the reproductive stage. Leaf water loss and leaf rolling tests distinguished these two groups from each other. Both 7 and 14 days of drought stress affected most of the tested agronomic traits including grain yield, and the effects were stronger in the drought-sensitive cultivars. Fourteen days of drought stress severely reduced grain yield in the sensitive cultivars. Expression levels of 50 genes previously published were examined in panicles. Of these, 25 genes were expressed in panicles and could be classified into 6 groups. LOC_Os02g51350, a Kelch domain-containing F-box gene, was selected for further studies including expression analysis in panicles during the 14-day drought stress, domain analysis, and analysis of cis-acting elements in the promoters. All three drought-resistant cultivars possessed the F-box domain, which was absent in the two drought-sensitive cultivars. In addition, drought-related ABRE and DRE/CRT cis-acting elements were more abundant in Os02g51350 promoters of cultivars with good grain yield under drought stress than in promoters of cultivars with severe yield reduction. Our results suggest that the F-box version of Os02g51350 is important for maintenance of grain yield under drought.     

Tolerance Associated Gene Expression following Allogeneic Hematopoietic Cell Transplantation

Biologic markers of immune tolerance may facilitate tailoring of immune suppression duration after allogeneic hematopoietic cell transplantation (HCT). In a cross-sectional study, peripheral blood samples were obtained from tolerant (n = 15, median 38.5 months post-HCT) and non-tolerant (n = 17, median 39.5 post-HCT) HCT recipients and healthy control subjects (n = 10) for analysis of immune cell subsets and differential gene expression. There were no significant differences in immune subsets across groups. We identified 281 probe sets unique to the tolerant (TOL) group and 122 for non-tolerant (non-TOL). These were enriched for process networks including NK cell cytotoxicity, antigen presentation, lymphocyte proliferation, and cell cycle and apoptosis. Differential gene expression was enriched for CD56, CD66, and CD14 human lineage-specific gene expression. Differential expression of 20 probe sets between groups was sufficient to develop a classifier with > 90% accuracy, correctly classifying 14/15 TOL cases and 15/17 non-TOL cases. These data suggest that differential gene expression can be utilized to accurately classify tolerant patients following HCT. Prospective investigation of immune tolerance biologic markers is warranted.     

六种园林植物耐旱性分析

为选择耐旱性较强的园林绿化植物,选择6种常见的园林植物：金银木（Lonicera maackii）、紫荆（Cercis chinensis）、紫薇（Lagerstroemia indica）、荆条（Vitex negundo var.heterophylla）、胡枝子（Lespedeza bicolor）和构树（Broussonetia papyrifera）,进行盆栽控水试验,对植株外观形态和土壤含水率、叶片叶绿素含量、超氧化物歧化酶（SOD）活性、丙二醛（MDA）含量进行比较。结果表明,随干旱胁迫时间的延长,土壤含水量均呈下降趋势,金银木、胡枝子和荆条的长势较好;紫薇、紫荆和构树出现叶片萎蔫、掉落现象,6种植物叶片的光合色素含量呈先上升后下降的趋势,除紫薇外,SOD活性总体均呈上升趋势,MDA含量持续上升。可见,金银木、胡枝子和荆条的耐旱性较强,紫薇、紫荆和构树的耐旱性较弱。     

PtrWRKY51基因的克隆及抗旱表达特性分析

为明确毛果杨WRKY家族成员PtrWRKY51基因功能,以Nisqually-1株系毛果杨为模板,克隆得到PtrWRKY51基因CDS序列。通过生物信息学分析,结合酵母自激活验证、亚细胞定位及模拟干旱胁迫下的实时荧光定量PCR(qRT-PCR)对PtrWRKY51基因功能进行初步研究。结果表明：PtrWRKY51全长579 bp,编码192 aa。生物信息学分析及亚细胞定位试验结果表明,PtrWRKY51蛋白为非跨膜碱性不稳定亲水蛋白,定位于细胞核,含有WRKY家族特有的保守结构域,是第IIc类WRKY转录因子;酵母自激活验证试验表明PtrWRKY51基因具有自激活活性;qRT-PCR分析表明,8%PEG6000模拟干旱胁迫下,该基因在胁迫12 h后茎部与叶部相对表达量达到最大值,根部则出现在24 h,研究可为PtrWRKY51抗逆及生物学功能进一步研究提供参考。     

Molecular Dissection of a Genomic Region Governing Root Traits Associated with Drought Tolerance Employing a Combinatorial Approach of QTL Mapping and RNA-seq in Rice

Drought is considered as one of the major obstacles for progressive yield enhancement and stability in rice, especially in rain-fed conditions. Being a complex trait, drought is regulated by numerous quantitative trait loci (QTL), of which, however, very few underlying genes have been cloned. In the present investigation, we made an attempt to uncover the candidate gene(s) behind a major QTL, rdw8.1 governing drought tolerance traits viz., root dry weight and root length. The targeted QTL has been delimited to 366.75 kb from 10.17 Mb by QTL mapping in BC₁F₂ population. Further, the targeted region was delineated employing next-generation sequencing based RNA-seq. Based on the QTL mapping and RNA-seq approaches, the plausible candidate gene underlying the QTL region was identified as a wound inducible protein (LOC_Os08g08090). This gene can be of potential value to enhance the drought tolerance of the elite rice varieties through molecular breeding.     

Alteration of Gene Expression Associated with Abscisic Acid-Induced Chilling Tolerance in Maize Suspension-Cultured Cells

ABA induces chilling tolerance in maize (Zea mays L., cv Black Mexican Sweet) suspension-cultured cells at 28[deg] C when ABA was added to the culture medium at least 6 h prior to chilling (4[deg] C), and this induction can be inhibited by blocking protein synthesis with cycloheximide treatment (Z. Xin, P.H. Li [1992] Plant Physiol 99: 707-711). De novo synthesis of proteins and changes in poly(A+) RNAs were investigated during the ABA induction of chilling tolerance at 28[deg] C as well as during chilling exposure. At 28[deg] C, ABA increased the net synthesis of 11 proteins. Five of these proteins, whose net synthesis was also increased by chilling (4[deg] C), were called group I ABA-induced proteins; the remaining six proteins, whose net synthesis was not altered by chilling, were called group II ABA-induced proteins. Chilling suppressed the net synthesis of three proteins. ABA treatment prior to chilling did not alleviate this suppression. ABA applied at the inception of chilling induced neither chilling tolerance nor accumulation of any of the group II proteins; however, once the group II proteins appeared, they were continually synthesized even in a chilling regimen. ABA induced seven in vitro translation products at 28[deg] C. Three of these products could also be induced by chilling; the remaining four were induced by ABA only at 28[deg] C. These results suggest that ABA-induced alteration of protein synthesis at 28[deg] C is associated with an increased chilling tolerance in maize suspension-cultured cells.     

敲除AMP1基因可以提高干旱响应基因的表达量从而增强拟南芥的抗旱能力

干旱严重影响植物的生长发育及农作物产量,因此研究植物的干旱反应机制显得至关重要.我们发现在拟南芥中一个推测的谷氨酸羧肽酶, AMP1, 其缺失突变体amp1的抗旱能力大大增强.基因芯片分析表明,amp1突变体抗旱能力的提高与许多干旱响应基因的高表达息息相关,例如,在amp1突变体中2个干旱诱导表达的转录因子基因,DREB2A和DREB1A的表达量升高;AT1G61340 (LEA 蛋白)的表达量也升高了很多,它在干旱条件下具有解毒和缓解细胞伤害的作用.而且,在amp1突变体中DREB2A 转录因子的2个下游基因RD29A 和COR47受干旱诱导的表达量和时间都比野生型中高和早. 在突变体中一些参与蛋白代谢、糖代谢和脂代谢的基因上调,一些保护和解毒相关基因表达量也升高,这些都可以给突变体在抗旱反应过程提供一定的保护作用.因此,我们认为AMP1基因在干旱胁迫反应中对干旱响应基因的表达起到一个负调控作用.实验中我们还发现, amp1突变体具有较低的水势与非常发达的根系,这也可能在抗旱反应中起到了一定作用.     

表达肌醇甲基转移酶基因载体的构建及转基因烟草的耐盐性研究

构建了肌醇甲基转移酶（Imt1）基因的植物表达载体pDH5, 通过农杆菌（Agrobacterium）介导,获得了转基因烟草(Nicotiana tabacum L. cv. SR1)植株,在附加1.2%～1.5% NaCl的生根培养基MSr(MSO 3 g/L蔗糖 7 g/L 葡萄糖)上可生根。 生化分析表明,不具有芒柄醇（D-ononitol）合成途径的烟草鲜叶片积累了100～654 nmol/g的芒柄醇, 新产生了一个代谢分支。Western杂交分析证明Imt1基因在烟草中的表达,从而为植物耐盐的基因工程育种提供了一条新途径。     

Expression of the Kale WRKY Gene BoWRKY10 in Transgenic Tobacco Confers Drought Stress Tolerance

Russian Journal of Plant Physiology - WRKYs play important roles in plant growth, defense regulation, and the stress response. However, the mechanisms through which WRKYs are involved in drought...     

表达肌醇甲基转移酶基因载体的构建及转基因烟草的耐盐性研究

构建了肌醇甲基转移酶（Imtl）基因的植物表达载体pDH5．通过农杆菌（Agrobacterium）介导,获得了转基因烟草（NicotianatabacumLev．SR1）植株,在附加1．2％－1．5％NaCl的生根培养基MSr（MSO＋3g／L蔗糖＋7g／L葡萄糖）上可生根。生化分析表明,不具有芒柄醇（D－ononitol）合成途径的烟草鲜叶片积累了100－654nmol／g的芒柄醇,新产生了一个代谢分支。Western杂交分析证明Imtl基因在烟草中的表达,从而为植物耐盐的基因工程育种提供了一条新途径。     

Atrazine Tolerance of Grass Species with Potential for Use in Vegetated Filters in Australia

The response of introduced (Pennisetum clandestinum Hochst.) and native (Stipa aristiglumis F. Muell., Themeda australis (R. Br.) Stapf, Danthonia spp. (L.) grasses to the herbicide atrazine was studied in plants with the potential for use in vegetated filters (biofilters) designed to reduce chemical loads in agricultural runoff. The response was detected by photosynthetic inhibition using leaf chlorophyll fluorescence. With continuous short-term (14 days) dosing with atrazine in sand culture, P. clandestinum showed the greatest tolerance, regardless of the dose (20–500 μg/L). In a clay vertosol soil in the glasshouse, the four species were tolerant to longer-term (84 days) application of three successive doses of simulated run-on, each dose containing 100 μg/L atrazine, a concentration which is comparable to the highest reported in runoff from agricultural land in Australia. Even with a subsequent single atrazine dose at ∼ ∼5000 μg/L, established plants of the four species showed signs of quick recovery (7–21 days) to normal photosynthetic activity. In a field experiment with simulated run-on, applied to P. clandestinum pasture in sandy loam soil, repeated doses at concentrations up to 1000 μg/L gave no significant response; only a subsequent single dose of 5000 μg/L had significant effects, from which plants soon recovered. Although damage from atrazine can be demonstrated with continuous dosing in non-adsorbing media, in soil culture the tolerance of the four selected species to repeat doses of atrazine shows they may be used confidently for biofiltering purposes. P. clandestinum was especially tolerant.