Efficient auto-excision of a selectable marker gene from transgenic citrus by combining the Cre/loxP system and ipt selection

Key message

A highly efficient Cre-mediated deletion system, offering a good alternative for producing marker-free transgenic plants that will relieve public concerns regarding GMOs, was first developed in citrus.

Abstract

The presence of marker genes in genetically modified crops raises public concerns regarding their safety. The removal of marker genes can prevent the risk of their flow into the environment and hasten the public’s acceptance of transgenic products. In this study, a new construct based on the Cre/loxP site-recombination system was designed to delete marker genes from transgenic citrus. In the construct, the selectable marker gene isopentenyltransferase gene (ipt) from Agrobacterium tumefaciens and the Cre recombinase gene were flanked by two loxP recognition sites in the direct orientation. The green fluorescent protein (gfp) reporter gene for monitoring the transformation of foreign genes was located outside of the loxP sequences. Transformation and deletion efficiencies of the vector were investigated using nopaline synthase gene (NosP) and CaMV 35S promoters to drive expression of Cre. Analysis of GFP activity showed that 28.1 and 13.6 % transformation efficiencies could be obtained by NosP- and CaMV 35S-driven deletions, respectively. Molecular analysis demonstrated that 100 % deletion efficiency was observed in the transgenic plants. The complete excision of the marker gene was found in all deletion events driven by NosP and in 81.8 % of deletion events driven by CaMV 35S. The results showed that Cre/loxP-mediated excision was highly efficient and precise in citrus. This approach provides a reliable strategy for auto-deletion of selectable marker genes from transgenic citrus to produce marker-free transgenic plants.     

2‐(Undecyloxy)‐ethanol is a major component of the male‐produced aggregation pheromone of Monochamus sutor

The small white‐marmorated longicorn beetle, Monochamus sutor (L.) (Coleoptera: Cerambycidae), is widely distributed throughout Europe and Asia. It is a potential vector of the pine wood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, the causal agent of the devastating pine wilt disease. Volatiles were collected from both male and female beetles after maturation feeding. In analyses of these collections using gas chromatography (GC) coupled to mass spectrometry, a single male‐specific compound was detected and identified as 2‐(undecyloxy)‐ethanol. In analyses by GC coupled to electroantennography the only consistent responses from both female and male antennae were to this compound. Trapping tests were carried out in Spain, Sweden, and China. 2‐(Undecyloxy)‐ethanol was attractive to both male and female M. sutor beetles. A blend of the bark beetle pheromones ipsenol, ipsdienol, and 2‐methyl‐3‐buten‐2‐ol was also attractive to both sexes in Spain and Sweden, and further increased the attractiveness of the 2‐(undecyloxy)‐ethanol. The host plant volatiles α‐pinene, 3‐carene, and ethanol were weakly attractive, if at all, in all three countries and did not significantly increase the attractiveness of the blend of 2‐(undecyloxy)‐ethanol and bark beetle pheromones. 2‐(Undecyloxy)‐ethanol is thus proposed to be the major, if not only, component of the male‐produced aggregation pheromone of M. sutor, and its role is discussed. This compound has been reported as a pheromone of several other Monochamus species and is another example of the parsimony that seems to exist among the pheromones of many of the Cerambycidae. Traps baited with 2‐(undecyloxy)‐ethanol and bark beetle pheromones should be useful for monitoring and control of pine wilt disease, should M. sutor be proven to be a vector of the nematode.     

Improved protocol for the transformation of adult Citrus sinensis Osbeck ‘Tarocco’ blood orange tissues

The production of transgenic citrus plants from adult tissues is difficult because of low regeneration and transformation rates. To increase the transformation efficiency of adult citrus tissues, an improved protocol involving adult Citrus sinensis Osbeck ‘Tarocco’ blood orange tissues was developed. Explants were pre-incubated in a liquid medium prior to infection by Agrobacterium tumefaciens. Plant materials were also incubated on callus-induction medium supplemented with various combinations of cytokinin (Cyt) and kanamycin (Kan). An appropriate pre-incubation of the explants increased the transformation efficiency of adult tissues. During the callus-induction period, the Cyt type and Kan concentration had the largest and smallest effects on the transformation efficiency, respectively. The most effective combination of plant growth regulator and Kan for the transformation of ‘Tarocco’ blood orange tissues was 2 mg L⁻¹ 2-isopentenyl adenine and 50 mg L⁻¹ Kan. The transformation efficiency under the optimized conditions was 11.7%. A Southern blot analysis confirmed the integration of the transgene. These results indicated that the transformation efficiency of adult citrus tissues can be enhanced by optimizing the transformation conditions.

     

CXCL10/IP-10 in infectious diseases pathogenesis and potential therapeutic implications

C–X–C motif chemokine 10 (CXCL10) also known as interferon γ-induced protein 10 kDa (IP-10) or small-inducible cytokine B10 is a cytokine belonging to the CXC chemokine family. CXCL10 binds CXCR3 receptor to induce chemotaxis, apoptosis, cell growth and angiostasis. Alterations in CXCL10 expression levels have been associated with inflammatory diseases including infectious diseases, immune dysfunction and tumor development. CXCL10 is also recognized as a biomarker that predicts severity of various diseases. A review of the emerging role of CXCL10 in pathogenesis of infectious diseases revealed diverse roles of CXCL10 in disease initiation and progression. The potential utilization of CXCL10 as a therapeutic target for infectious diseases is discussed.     

鉴别无色素性恶性黑色素瘤方法的探讨

无色素及少色素性恶黑鉴别诊断时,（１）组织化学铁反应,褪色素和黑色素银染对证实瘤细胞中黑色素是有帮助的,但不能从无色素性恶黑中检出黑色素。因此对无黑色素恶黑的诊断和鉴别诊断帮助不大。网状纤维染色良性病均有增加,而恶黑几乎没有增加或仅极少增加。因此网状纤维染色有助于良恶性的鉴别。（２）免疫组化Ｓ－１００１８例恶黑及６例良性痣均显示阳性,这对无色素恶黑的诊断是有价值的,但对色素痣的恶变帮助不大。１６例恶黑中１４例色素性与１０例无色素性恶黑ＨＭＢ４５均显示阳性,证明两者有共同抗原,总阳性率８７．５％,６例良性痣均为阴性,证明无ＨＭＢ４５抗原。结果提示ＨＭＢ４５免疫组化检测不仅对无色素及少色素性恶黑的诊断与鉴别诊断实用性大,还可以用于对恶黑与良性痣、良性痣恶变的鉴别。（３）本组４例无色素性恶黑电镜下均找到前黑色素小体。因此在其他方法诊断困难时,应用电镜检查对确诊具有决定性作用。     

Maternal cigarette smoking, metabolic gene polymorphisms, and preterm delivery: new insights on G×E interactions and pathogenic pathways

Preterm delivery (PTD, <37 weeks of gestation) is a significant clinical and public health problem. Previously, we reported that maternal smoking and metabolic gene polymorphisms of CYP1A1 MspI and GSTT1 synergistically increase the risk of low birth weight. This study investigates the relationship between maternal smoking and metabolic gene polymorphisms of CYP1A1 MspI and GSTT1 with preterm delivery (PTD) as a whole and preterm subgroups. This case–control study included 1,749 multi-ethnic mothers (571 with PTD and 1,178 controls) enrolled at Boston Medical Center. After adjusting covariates, regression analyses were performed to identify individual and joint associations of maternal smoking, two functional variants of CYP1A1 and GSTT1 with PTD. We observed a moderate effect of maternal smoking on PTD (OR = 1.6; 95% CI: 1.1–2.2). We found that compared to non-smoking mothers with low-risk genotypes, there was a significant joint association of maternal smoking, CYP1A1 (Aa/aa) and GSTT1 (absent) genotypes with gestational age (β = −3.37; SE = 0.86; P = 9 × 10⁻⁵) and with PTD (OR = 5.8; 95% CI: 2.0–21.1), respectively. Such joint association was particularly strong in certain preterm subgroups, including spontaneous PTD (OR = 8.3; 95% CI: 2.7–30.6), PTD < 32 weeks (OR = 11.1; 95% CI: 2.9–47.7), and PTD accompanied by histologic chorioamnionitis (OR = 15.6; 95% CI: 4.1–76.7). Similar patterns were observed across ethnic groups. Taken together, maternal smoking significantly increased the risk of PTD among women with high-risk CYP1A1 and GSTT1 genotypes. Such joint associations were strongest among PTD accompanied by histologic chorioamnionitis. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Occupational Electromagnetic Field Exposures Associated with Sleep Quality: A Cross-Sectional Study

Background

Exposure to electromagnetic field (EMF) emitted by mobile phone and other machineries concerns half the world’s population and raises the problem of their impact on human health. The present study aims to explore the effects of electromagnetic field exposures on sleep quality and sleep duration among workers from electric power plant.

Methods

A cross-sectional study was conducted in an electric power plant of Zhejiang Province, China. A total of 854 participants were included in the final analysis. The detailed information of participants was obtained by trained investigators using a structured questionnaire, which including socio-demographic characteristics, lifestyle variables, sleep variables and electromagnetic exposures. Physical examination and venous blood collection were also carried out for every study subject.

Results

After grouping daily occupational electromagnetic exposure into three categories, subjects with long daily exposure time had a significantly higher risk of poor sleep quality in comparison to those with short daily exposure time. The adjusted odds ratios were 1.68 (95%CI: 1.18, 2.39) and 1.57 (95%CI: 1.10, 2.24) across tertiles. Additionally, among the subjects with long-term occupational exposure, the longer daily occupational exposure time apparently increased the risk of poor sleep quality (OR (95%CI): 2.12 (1.23∼3.66) in the second tertile; 1.83 (1.07∼3.15) in the third tertile). There was no significant association of long-term occupational exposure duration, monthly electric fee or years of mobile-phone use with sleep quality or sleep duration.

Conclusions

The findings showed that daily occupational EMF exposure was positively associated with poor sleep quality. It implies EMF exposure may damage human sleep quality rather than sleep duration.