MfbHLH38, a Myrothamnus flabellifolia bHLH transcription factor, confers tolerance to drought and salinity stresses in Arabidopsis.

BACKGROUND: The basic helix-loop-helix (bHLH) proteins, a large transcription factors family, are involved in plant growth and development, and defensive response to various environmental stresses. The resurrection plant Myrothamnus flabellifolia is known for its extremely strong drought tolerance, but few bHLHs taking part in abiotic stress response have been unveiled in M. flabellifolia. RESULTS: In the present research, we cloned and characterized a dehydration-inducible gene, MfbHLH38, from M. flabellifolia. The MfbHLH38 protein is localized in the nucleus, where it may act as a transcription factor. Heterologous expression of MfbHLH38 in Arabidopsis improved the tolerance to drought and salinity stresses, as determined by the studies on physiological indexes, such as contents of chlorophyll, malondialdehyde (MDA), proline (Pro), soluble protein, and soluble sugar, water loss rate of detached leaves, reactive oxygen species (ROS) accumulation, as well as antioxidant enzyme activities. Besides, MfbHLH38 overexpression increased the sensitivity of stomatal closure to mannitol and abscisic acid (ABA), improved ABA level under drought stress, and elevated the expression of genes associated with ABA biosynthesis and ABA responding, sucha as NCED3, P5CS, and RD29A. CONCLUSIONS: Our results presented evidence that MfbHLH38 enhanced tolerance to drought and salinity stresses in Arabidopsis through increasing water retention ability, regulating osmotic balance, decreasing stress-induced oxidation damage, and possibly participated in ABA-dependent stress-responding pathway.

MfPIF1 of Resurrection Plant Myrothamnus flabellifolia Plays a Positive Regulatory Role in Responding to Drought and Salinity Stresses in Arabidopsis.

Phytochrome-interacting factors (PIFs), a subfamily of basic helix-loop-helix (bHLH) transcription factors (TFs), play critical roles in regulating plant growth and development. The resurrection plant Myrothamnus flabellifolia possesses a noteworthy tolerance to desiccation, but no PIFs related to the response to abiotic stress have been functionally studied. In this study, a dehydration-inducible PIF gene, MfPIF1, was cloned and characterized. Subcellular localization assay revealed that MfPIF1 is localized predominantly in the nucleus. Overexpression of MfPIF1 in Arabidopsis thaliana led to enhanced drought and salinity tolerance, which was attributed to higher contents of chlorophyll, proline (Pro), soluble protein, and soluble sugar, activities of antioxidant enzymes as well as lower water loss rate, malondialdehyde (MDA) content, and reactive oxygen species (ROS) accumulation in transgenic lines compared with control plants. Moreover, MfPIF1 decreased stomatal aperture after drought and abscisic acid (ABA) treatment, and increased expression of both ABA biosynthesis and ABA-responsive genes including NCED3, P5CS, and RD29A. Overall, these results indicated that MfPIF1 may act as a positive regulator to drought and salinity responses, and therefore could be considered as a potential gene for plant genetic improvement of drought and salinity tolerance.

Comparative genomics analysis reveals gene family expansion and changes of expression patterns associated with natural adaptations of flowering time and secondary metabolism in yellow Camellia.

Yellow-flowering species are unique in the genus Camellia not only for their bright yellow pigments but also the health-improving substances in petals. However, little is known regarding the biosynthesis pathways of pigments and secondary metabolites. Here, we performed comparative genomics studies in two yellow-flowered species of the genus Camellia with distinctive flowering periods. We obtained 112,190 and 89,609 unigenes from Camellia nitidissima and Camellia chuongtsoensis, respectively, and identified 9547 gene family clusters shared with various plant species and 3414 single-copy gene families. Global gene expression analysis revealed six comparisons of differentially expressed gene sets in different developmental stages of floral bud. Through the identification of orthologous pairs, conserved and specific differentially expressed genes (DEGs) between species were compared. Functional enrichment analysis suggested that the gibberellin (GA) biosynthesis pathway might be related to the alteration of flowering responses. Furthermore, the expression patterns of secondary metabolism pathway genes were analyzed between yellow- and red-flowered Camellias. We showed that the key enzymes involved in glycosylation of flavonoids displayed differential expression patterns, indicating that the direct glycosylation of flavonols rather than anthocyanins was pivotal to coloration and health-improving metabolites in the yellow Camellia petals. Finally, the gene family analysis of UDP-glycosyltransferases revealed an expansion of group C members in C. nitidissima. Through comparative genomics analysis, we demonstrate that changes of gene expression and gene family members are critical to the variation of natural traits. This work provides valuable insights into the molecular regulation of trait adaptations of floral pigmentation and flowering timing.

Assessment of the contribution of chiral odorants to aroma property of baked green teas using an efficient sequential stir bar sorptive extraction approach.

Chiral volatile compounds are known to be distributed in teas at various enantiomeric ratios. However, the performance of each enantiomer, including aroma characteristics, aroma intensities, and contribution to the overall flavor of tea, is still unclear. In this study, aroma characteristics and intensities of 38 volatile enantiomers in standards and baked green teas with chestnut-like aroma and clean aroma were evaluated by an efficient sequential headspace-stir bar sorptive extraction (seq-HS-SBSE) approach combined with the enantioselective gas chromatography-olfactometry/mass spectrometry (Es-GC-O/MS) technique. Moreover, aroma recombination results for the two types of baked green teas using 14 chiral odorants and four achiral odorants indicated that the combinations of the detected odorants mainly contributed to the "floral", "sweet", and "chestnut-like" aromas. R-Linalool simultaneously enhanced the "floral", "sweet", and "chestnut-like" aromas; R-limonene mainly contributed to the "sweet" and "clean" aromas; and S-α-terpineol promoted the "sweet" and "floral" aromas of baked green tea.

Dehydration-Induced WRKY Transcriptional Factor MfWRKY70 of Myrothamnus flabellifolia Enhanced Drought and Salinity Tolerance in Arabidopsis.

The resurrection plants Myrothamnus flabellifolia can survive long term severe drought and desiccation conditions and soon recover after rewatering. However, few genes related to such excellent drought tolerance and underlying molecular mechanism have been excavated. WRKY transcription factors play critical roles in biotic and abiotic stress signaling, in which WRKY70 functions as a positive regulator in biotic stress response but a negative regulator in abiotic stress signaling in Arabidopsis and some other plant species. In the present study, the functions of a dehydration-induced MfWRKY70 of M. flabellifolia participating was investigated in the model plant Arabidopsis. Our results indicated that MfWRKY70 was localized in the nucleus and could significantly increase tolerance to drought, osmotic, and salinity stresses by promoting root growth and water retention, as well as enhancing the antioxidant enzyme system and maintaining reactive oxygen species (ROS) homeostasis and membrane-lipid stability under stressful conditions. Moreover, the expression of stress-associated genes (P5CS, NCED3 and RD29A) was positively regulated in the overexpression of MfWRKY70 Arabidopsis. We proposed that MfWRKY70 may function as a positive regulator for abiotic stress responses and can be considered as a potential gene for improvement of drought and salinity tolerance in plants.

[Preparation of polyclonal and monoclonal antibodies against CRF and change of CRF in the sleep-deprived rat brain].

AIM: To produce polyclonal and monoclonal antibodies against corticotropin-releasing factor (CRF) and to study the changes of CRF in sleep-deprived rat brain with the antibodies acquired. METHODS: Commercial CRF was linked to bovine throglobulin (BTG) and bovine serum albumin (BSA) respectively to produce immunogen and embedding antigen. New Zealand rabbits and BALB/c mice were immunized with the BTG-CRF immunogen to produce polyclonal and monoclonal antibodies, respectively. The acquired antibodies were appraised with ELISA and immnohistochemical staining. The characterized antibodies were used to observe the changes of CRF in the rat brain 48 h after sleep deprivation. RESULTS: CRF polyclonal antibody and 9 clones of monoclonal antibodies were obtained with high titer, affinity and specificity. Among them, the polyclonal antibody and 2 monoclonal antibodies (1D10, 2F4) were excellent in immunocytochemical staining. The CRF-like immunoreactive substances were found more strongly expressed in the neurons of paraverticular hypothalamic nucleus (PVN), central subnucleus of amygdala (CeA), oval subnucleus of bed nucleus of stria terminalis (BNSTov), and nucleus of solitary tract (NTS) in sleep-deprived rat brain. While they were much weaker and even absent in the control. CONCLUSION: The polyclonal and monoclonal antibodies against CRF were successfully produced for immunocytochemical studies. The results indicate that CRF may play an important role in stress-responsive modulation during sleep deprivation. PVN, CeA and BNSTov are integral part of brain circuit related to the stress modulation.

[Effects of simulated high altitude hypoxia on cognitive performance].

AIM: To investigate the effects of mild and moderate hypoxia on human cognitive performance. METHODS: Eighteen healthy young male volunteers performed a set of tests of human ergonomics at sea level (300 m in Xi'an) and simulated high altitude of 2 800 m, 3 600 m and 4 400 m for 1 h in hypobaric chamber, respectively. RESULTS: The performance of continuous recognition memory tests compared with the controls' was deteriorated significantly (P < 0.01) after exposure to 2 800 m for 1 h. After exposure to 3 600 m for 1 h, in all test, the reaction time was much longer, the accurate rates were lower and the performance was worse than that of control (P < 0.05). All the parameters were deteriorated with the increment of altitude and the performance of all tests were much worse at 4 300 m for 1 h (P < 0.01). CONCLUSION: Different parameters of human cognitive performance may have different susceptible thresholds to hypoxia according to the results from our studies. The cognitive performance after exposure to 3 600 m for 1 h was not sufficiently effective for the demands of human ergonomics due to its significant deteriorating changes. However, the performance can be effectively restored after exposure to enough oxygen supply for 1 h.