A Single Nasal Dose Vaccination with a Brucella abortus Mutant Potently Protects against Pulmonary Infection.

The Brucella abortus double-mutant (ΔznuA ΔnorD Brucella abortus-lacZ [znBAZ]) was assessed for its protective efficacy after vaccination with a single nasal dose. Superior protection was achieved in znBAZ-vaccinated mice against pulmonary, wild-type B. abortus 2308 challenge when compared with conventional livestock Brucella abortus vaccines, the smooth S19 (smooth B. abortus strain 19 vaccine) and rough RB51 (rough mutant vaccine strain of B. abortus) strains. Nasal znBAZ vaccination reduced splenic and lung colonization by wild-type brucellae by >3-4 logs. In contrast, S19 reduced lung colonization by only 32-fold, and RB51 failed to reduce colonization. One profound attribute of znBAZ vaccination was the >3-fold increase in pulmonary CD8+ T cells when compared with other vaccinated groups. S19 vaccination increased only CD4+ T cells. All vaccines induced IFN-γ and TNF-α production by CD4+ T cells, but only znBAZ vaccination enhanced the recruitment of polyfunctional CD8+ T cells, by >100-fold. IL-17 by both CD4+ and CD8+ T cells was also induced by subsequent znBAZ vaccination. These results demonstrate that, in addition to achieving protective immunity by CD4+ T cells, CD8+ T cells, specifically resident memory T cells, also confer protection against brucellosis. The protection obtained by znBAZ vaccination was attributed to IFN-γ-producing CD8+ T cells, because depletion of CD8+ T cells throughout vaccination and challenge phases abrogated protection. The stimulation of only CD4+ T cells by RB51- and S19-vaccinated mice proved insufficient in protecting against pulmonary B. abortus 2308 challenge. Thus, nasal znBAZ vaccination offers an alternative means to elicit protection against brucellosis.

StICE1 enhances plant cold tolerance by directly upregulating StLTI6A expression.

KEY MESSAGE: Under cold conditions, StICE1 enhances plant cold tolerance by upregulating StLTI6A expression to maintain the cell membrane stability. Cold stress affects potato plants growth and development, crop productivity and quality. The ICE-CBF-COR regulatory cascade is the well-known pathway in response to cold stress in plants. ICE1, as a MYC-like bHLH transcription factor, can regulate the expressions of CBFs. However, whether ICE1 could regulate other genes still need to be explored. Our results showed that overexpressing ICE1 from potato in Arabidopsis thaliana could enhance plant cold tolerance. Under cold stress, overexpressed StICE1 in plants improved the stability of cell membrane, enhanced scavenging capacity of reactive oxygen species and increased expression levels of CBFs and COR genes. Furthermore, StICE1 could bind to the promoter of StLTI6A gene, which could maintain the stability of the cell membrane, to upregulate StLTI6A expression under cold conditions. Our findings revealed that StICE1 could directly regulate StLTI6A, CBF and COR genes expression to response to cold stress.

The network centered on ICEs play roles in plant cold tolerance, growth and development.

MAIN CONCLUSION: ICEs are key transcription factors in response to cold in plant, they also balance plant growth and stress tolerance. Thus, we systematize the information about ICEs published to date. Low temperature is an important factor affecting plant growth and development. Exposing to cold condition results in a suit of effects on plants including reduction of plant growth and reproduction, and decrease in crop yield and quality. Plants have evolved a series of strategies to deal with cold stress such as reprogramming of the expression of genes and transcription factors. ICEs (Inducer of CBF Expression), as transcription factors regulating CBFs (C-repeat binding factor), play key roles in balancing plant growth and stress tolerance. Studies on ICEs focused on the function of ICEs on cold tolerance, growth and development; post-translational modifications of ICEs and crosstalk between the ICEs and phytohormones. In this review, we focus on systematizing the information published to date. We summarized the main advances of the functions of ICEs on the cold tolerance, growth and development. And we also elaborated the regulation of ICEs protein stability including phosphorylation, ubiquitination and SUMOylation of ICE. Finally, we described the function of ICEs in the crosstalk among different phytohormone signaling pathway and cold stress. This review provides perspectives for ongoing research about cold tolerance, growth and development in plant.

Targeting resident memory T cell immunity culminates in pulmonary and systemic protection against Brucella infection.

Brucellosis remains the most common zoonotic disease globally. Currently no vaccines for humans exist, and conventional brucellosis vaccines for livestock fail to confer complete protection; hence, an improved vaccine is needed. Although Brucella infections primarily occur following a mucosal exposure, vaccines are administered parenterally. Few studies have considered mucosal vaccinations, or even targeting of tissue-resident memory T (TRM) cells. TRM cells protect against viral infections, but less is known of their role in bacterial infections, and even less for brucellosis. Oral prime, nasal boost with a newly developed Brucella abortus double mutant (znBAZ) confers nearly complete protection against pulmonary challenge with wild-type (wt) B. abortus 2308, and its protective efficacy is >2800-fold better than the RB51 vaccine. Vaccination with znBAZ potently stimulated CD8+ T cells, whereas mucosal vaccination with RB51 induced mostly CD4+ T cells. Subsequent analysis revealed these pulmonary CD44+ CD69+ CD8+ T cells to be either CD103+ or CD103- TRM cells, and these sequestered to the lung parenchyma as CXCR3lo and to the airways as CXCR3hi. Both CD8+ TRM subsets contained single-positive IFN-γ and TNF-α, as well as, polyfunctional cells. IL-17-producing CD8+ TRM cells were also induced by znBAZ vaccination, but in vivo IL-17 neutralization had no impact upon protection. In vivo depletion of CD4+ T cells had no impact upon protection in znBAZ-vaccinated mice. In contrast, CD4+ T cell depletion reduced RB51's protective efficacy in spleens and lungs by two- and three-logs, respectively. Although anti-CD8 mAb-treated znBAZ-vaccinated mice showed a significantly reduced pulmonary efficacy, this treatment failed to completely deplete the lung CD8+ T cells, leaving the CD103+ and CD103- CD8+ TRM cell ratios intact. Only znBAZ-vaccinated CD8-/- mice were fully sensitive to pulmonary challenge with virulent wt B. abortus 2308 since CD8+ TRM cells could not be induced. Collectively, these data demonstrate the key role of mucosal vaccination for the generation of CD8+ TRM cells in protecting against pulmonary challenge with virulent B. abortus.

Diversity of responses to nitrogen deficiency in distinct wheat genotypes reveals the role of alternative electron flows in photoprotection.

Nitrogen (N) deficiency represents an important limiting factor affecting photosynthetic productivity and the yields of crop plants. Significant reported differences in N use efficiency between the crop species and genotypes provide a good background for the studies of diversity of photosynthetic and photoprotective responses associated with nitrogen deficiency. Using distinct wheat (Triticum aestivum L.) genotypes with previously observed contrasting responses to nitrogen nutrition (cv. Enola and cv. Slomer), we performed advanced analyses of CO2 assimilation, PSII, and PSI photochemistry, also focusing on the heterogeneity of the stress responses in the different leaf levels. Our results confirmed the loss of photosynthetic capacity and enhanced more in lower positions. Non-stomatal limitation of photosynthesis was well reflected by the changes in PSII and PSI photochemistry, including the parameters derived from the fast-fluorescence kinetics. Low photosynthesis in N-deprived leaves, especially in lower positions, was associated with a significant decrease in the activity of alternative electron flows. The exception was the cyclic electron flow around PSI that was enhanced in most of the samples with a low photosynthetic rate. We observed significant genotype-specific responses. An old genotype Slomer with a lower CO2 assimilation rate demonstrated enhanced alternative electron flow and photorespiration capacity. In contrast, a modern, highly productive genotype Enola responded to decreased photosynthesis by a significant increase in nonphotochemical dissipation and cyclic electron flow. Our results illustrate the importance of alternative electron flows for eliminating the excitation pressure at the PSII acceptor side. The decrease in capacity of electron acceptors was balanced by the structural and functional changes of the components of the electron transport chain, leading to a decline of linear electron transport to prevent the overreduction of the PSI acceptor side and related photooxidative damage of photosynthetic structures in leaves exposed to nitrogen deficiency.

StATL2-like could affect growth and cold tolerance of plant by interacting with StCBFs.

KEY MESSAGE: Our results confirmed that StATL2-like could interact with StCBFs and regulate plant growth. Meanwhile, StATL2-like acted as a negative regulator on low-temperature tolerance in plants. As important transcription factors for resisting many kinds of stresses, C-repeat-binding factors (CBF) play a key role in plant low-temperature tolerance by increasing COR genes expressions. Here, we report that StATL2-like, a RING-H2 E3 ubiquitin in Solanum tuberosum L., interacted with StCBF1 and StCBF4, respectively. AtATL2 is a highly homologous gene of StATL2-like in Arabidopsis thaliana. Under normal conditions, atl2 Arabidopsis mutant showed a growth inhibition phenotype while overexpressed StATL2-like in wild type Arabidopsis and atl2 mutant promoted plant growth. Besides, atl2 mutant had better low-temperature tolerance compared with wild type and StATL2-like transgenic lines which demonstrated that StATL2-like acted as a negatively regulator on low-temperature tolerance in plant. Moreover, atl2 mutant improved the scavenging capacity of reactive oxygen species (ROS) and alleviate the damage of photosynthetic system II (PSII) compared with StATL2-like transgenic lines under cold conditions. These results suggested a new component in CBF-dependent pathway to regulate plant growth and response to low-temperature stress in potato plants.

Glycinebetaine mitigates tomato chilling stress by maintaining high-cyclic electron flow rate of photosystem I and stability of photosystem II.

KEY MESSAGE: Glycinebetaine alleviates chilling stress by protecting photosystems I and II in BADH-transgenic and GB-treated tomato plants, which can be an effective strategy for improving crop chilling tolerance. Tomato (Solanum lycopersicum) is one of the most cultivated vegetables in the world, but is highly susceptible to chilling stress and does not naturally accumulate glycinebetaine (GB), one of the most effective stress protectants. The protective mechanisms of GB on photosystem I (PSI) and photosystem II (PSII) against chilling stress, however, remain poorly understood. Here, we address this problem through exogenous GB application and generation of transgenic tomatoes (Moneymaker) with a gene encoding betaine aldehyde dehydrogenase (BADH), which is the key enzyme in the synthesis of GB, from spinach. Our results demonstrated that GB can protect chloroplast ultramicrostructure, alleviate PSII photoinhibition and maintain PSII stability under chilling stress. More importantly, GB increased the electron transfer between QA and QB and the redox potential of QB and maintained a high rate of cyclic electron flow around PSI, contributing to reduced production of reactive oxygen species, thereby mitigating PSI photodamage under chilling stress. Our results highlight the novel roles of GB in enhancing chilling tolerance via the protection of PSI and PSII in BADH transgenic and GB-treated tomato plants under chilling stress. Thus, introducing GB-biosynthetic pathway into tomato and exogenous GB application are effective strategies for improving chilling tolerance.

Electron and proton transport in wheat exposed to salt stress: is the increase of the thylakoid membrane proton conductivity responsible for decreasing the photosynthetic activity in sensitive genotypes?

Effects of salinity caused by 150 mM NaCl on primary photochemical reactions and some physiological and biochemical parameters (K+/Na+ ratio, soluble sugars, proline, MDA) have been studied in five Triticum aestivum L. genotypes with contrasting salt tolerance. It was found that 150 mM NaCl significantly decreased the photosynthetic efficiency of two sensitive genotypes. The K+/Na+ ratio decreased in all genotypes exposed to salinity stress when compared with the control. Salinity stress also caused lipid peroxidation and accumulation of soluble sugars and proline. The amounts of soluble sugars and proline were higher in tolerant genotypes than sensitive ones, and lipid peroxidation was higher in sensitive genotypes. The noninvasive measurements of photosynthesis-related parameters indicated the genotype-dependent effects of salinity stress on the photosynthetic apparatus. The significant decrease of chlorophyll content (SPAD values) or adverse effects on photosynthetic functions at the PSII level (measured by the chlorophyll fluorescence parameters) were observed in the two sensitive genotypes only. Although the information obtained by different fast noninvasive techniques were consistent, the correlation analyses identified the highest correlation of the noninvasive records with MDA, K+/Na+ ratio, and free proline content. The lower correlation levels were found for chlorophyll content (SPAD) and Fv/Fm values derived from chlorophyll fluorescence. Performance index (PIabs) derived from fast fluorescence kinetics, and F735/F685 ratio correlated well with MDA and Na+ content. The most promising were the results of linear electron flow measured by MultispeQ sensor, in which we found a highly significant correlation with all parameters assessed. Moreover, the noninvasive simultaneous measurements of chlorophyll fluorescence and electrochromic band shift using this sensor indicated the apparent proton leakage at the thylakoid membranes resulting in a high proton conductivity (gH+), present in sensitive genotypes only. The possible consequences for the photosynthetic functions and the photoprotection are discussed.

Glycinebetaine mitigated the photoinhibition of photosystem II at high temperature in transgenic tomato plants.

Photosystem II (PSII), especially the D1 protein, is highly sensitive to the detrimental impact of heat stress. Photoinhibition always occurs when the rate of photodamage exceeds the rate of D1 protein repair. Here, genetically engineered codA-tomato with the capability to accumulate glycinebetaine (GB) was established. After photoinhibition treatment at high temperature, the transgenic lines displayed more thermotolerance to heat-induced photoinhibition than the control line. GB maintained high expression of LeFtsHs and LeDegs and degraded the damaged D1 protein in time. Meanwhile, the increased transcription of synthesis-related genes accelerated the de novo synthesis of D1 protein. Low ROS accumulation reduced the inhibition of D1 protein translation in the transgenic plants, thereby reducing protein damage. The increased D1 protein content and decreased phosphorylated D1 protein (pD1) in the transgenic plants compared with control plants imply that GB may minimize photodamage and maximize D1 protein stability. As D1 protein exhibits a high turnover, PSII maybe repaired rapidly and efficiently in transgenic plants under photoinhibition treatment at high temperature, with the resultant mitigation of photoinhibition of PSII.

Photosynthesis research under climate change.

Increasing global population and climate change uncertainties have compelled increased photosynthetic efficiency and yields to ensure food security over the coming decades. Potentially, genetic manipulation and minimization of carbon or energy losses can be ideal to boost photosynthetic efficiency or crop productivity. Despite significant efforts, limited success has been achieved. There is a need for thorough improvement in key photosynthetic limiting factors, such as stomatal conductance, mesophyll conductance, biochemical capacity combined with Rubisco, the Calvin-Benson cycle, thylakoid membrane electron transport, nonphotochemical quenching, and carbon metabolism or fixation pathways. In addition, the mechanistic basis for the enhancement in photosynthetic adaptation to environmental variables such as light intensity, temperature and elevated CO2 requires further investigation. This review sheds light on strategies to improve plant photosynthesis by targeting these intrinsic photosynthetic limitations and external environmental factors.

Overexpression of ZmDHN11 could enhance transgenic yeast and tobacco tolerance to osmotic stress.

KEY MESSAGE: Maize group II LEA protein ZmDHN11 could protect protein activity and confer resistance to osmotic stress on transgenic yeast and tobacco. Late embryogenesis abundant (LEA) proteins are widely assumed to play crucial roles in environmental stress tolerance, but their function has remained obscure. Dehydrins are group II LEA proteins, which are highly hydrophilic plant stress proteins. In the present study, a novel group II LEA protein, ZmDHN11, was cloned and identified from maize. The expression of ZmDHN11 was induced by high osmotic stress, low temperature, salinity, and ABA (abscisic acid). The ZmDHN11 protein specifically accumulated in the nuclei and cytosol. Further study indicated that ZmDHN11 is phosphorylated by the casein kinase CKII. ZmDHN11 protected the activity of LDH under water-deficit stress. The overexpression of ZmDHN11 endows transgenic yeast and tobacco with tolerance to osmotic stress.

Glycinebetaine: a versatile protectant to improve rice performance against aluminium stress by regulating aluminium uptake and translocation.

KEY MESSAGE: Glycinebetaine alleviates the detrimental effects of aluminium stress by regulating aluminium uptake and translocation, maintaining PSII activity, and activating the oxidative defence, thereby maintaining the growth and development of rice. Aluminium (Al) toxicity is one of the primary growth-limiting factors that limits plant growth and crop productivity in acidic soils. Rice (Oryza sativa L.) plants are susceptible to Al stress and do not naturally accumulate glycinebetaine (GB), one of the most effective protectants. Therefore, the objective of this study was to investigate whether exogenous GB can ameliorate the detrimental effects of Al stress on rice plants. Our results showed that the growth, development and biomass of rice were clearly inhibited under Al stress. However, exogenous GB application increased rice shoot growth and photosynthetic pigments contents, maintained photosystem II (PSII) activity, and activated the antioxidant defence system under Al stress. More importantly, GB may mediate the expression of Al uptake- and translocation-related genes, including OsALS1, OsNrat1, OsSTAR1 and OsSTAR2, and the galacturonic acid contents in rice roots under Al stress. Therefore, our findings highlight exogenous GB application is a valid approach to effectively combat Al toxicity by regulating physiological and biochemical processes in crops.

Comparative effects of glycinebetaine on the thermotolerance in codA- and BADH-transgenic tomato plants under high temperature stress.

KEY MESSAGE: We propose that codA tomato plants exhibited higher degrees of enhanced thermotolerance than BADH tomato plants, and H2O2 as a signaling molecule also plays an important role in heat resistance. Betaine aldehyde dehydrogenase (BADH) and choline oxidase (COD) are key enzymes in glycinebetaine (GB) synthesis. In this study, two kinds of transgenic tomato plants, which were transformed with BADH gene and codA gene, respectively, were used to explore their thermotolerance. Our results showed that the levels of GB in leaves of the fourteen independent transgenic lines ranged from 1.9 µmol g-1 fresh weight to 3.4 µmol g-1 fresh weight, while GB was almost undetectable in leaves of WT plants. CO2 assimilation and photosystem II (PSII) photochemical activity in transgenic plants were more thermotolerant than WT plants, especially the codA-transgenic plants showed the most. Significant accumulation of hydrogen peroxide (H2O2), superoxide anion radical (O2·-), and malondialdehyde (MDA) were more in WT plants than transgenic plants, while this accumulation in codA-transgenic plant was the least. Furthermore, the expression of the heat response genes and the accumulation of heat shock protein 70 (HSP70) were found to be more in transgenic plants than that in WT plants during heat stress, as well as showing the most expression and accumulation of HSP70 in the codA-transgenic plants. Taken together, our results suggest that the enhanced thermotolerance in transgenic plants is due to the positive role of GB in response to heat stress. And interestingly, in addition to the major role of GB in codA-transgenic plants, H2O2 as a signaling molecule may also play an important role in heat resistance, leading to higher thermotolerance compared to BADH-transgenic plants.

Roles of YABBY transcription factors in the modulation of morphogenesis, development, and phytohormone and stress responses in plants.

The YABBY family is a class of plant-specific transcription factors comprising a typical N-terminal C2C2-type zinc finger domain and a C-terminal helix-loop-helix YABBY domain. YABBY transcription factors play important roles in multiple biological processes, including polarity establishment in plant leaves, the formation and development of reproductive organs, the response to plant hormone signals, resistance to stress, crop breeding and agricultural production. The aim of this review is to summarize our current understanding of the roles, functions and value of the YABBY family in plants, with particular emphasis on new insights into the molecular and physiological mechanisms involved in the YABBY-mediated modulation of polarity establishment, morphogenesis and development, and phytohormone and stress responses in plants. In addition, we propose that this transcription factor family presents great value and potential for research, application and development in crop breeding and agricultural production in the future.

Correction to: Accumulation of glycine betaine in transplastomic potato plants expressing choline oxidase confers improved drought tolerance.

Unfortunately, one of the author names has been misspelled in the original publication. The correct spelling is Qiping Song.

Accumulation of glycine betaine in transplastomic potato plants expressing choline oxidase confers improved drought tolerance.

MAIN CONCLUSION: Plastid genome engineering is an effective method to generate drought-resistant potato plants accumulating glycine betaine in plastids. Glycine betaine (GB) plays an important role under abiotic stress, and its accumulation in chloroplasts is more effective on stress tolerance than that in cytosol of transgenic plants. Here, we report that the codA gene from Arthrobacter globiformis, which encoded choline oxidase to catalyze the conversion of choline to GB, was successfully introduced into potato (Solanum tuberosum) plastid genome by plastid genetic engineering. Two independent plastid-transformed lines were isolated and confirmed as homoplasmic via Southern-blot analysis, in which the mRNA level of codA was much higher in leaves than in tubers. GB accumulated in similar levels in both leaves and tubers of codA-transplastomic potato plants (referred to as PC plants). The GB content was moderately increased in PC plants, and compartmentation of GB in plastids conferred considerably higher tolerance to drought stress compared to wild-type (WT) plants. Higher levels of relative water content and chlorophyll content under drought stress were detected in the leaves of PC plants compared to WT plants. Moreover, PC plants presented a significantly higher photosynthetic performance as well as antioxidant enzyme activities during drought stress. These results suggested that biosynthesis of GB by chloroplast engineering was an effective method to increase drought tolerance.

Wheat plant selection for high yields entailed improvement of leaf anatomical and biochemical traits including tolerance to non-optimal temperature conditions.

Assessment of photosynthetic traits and temperature tolerance was performed on field-grown modern genotype (MG), and the local landrace (LR) of wheat (Triticum aestivum L.) as well as the wild relative species (Aegilops cylindrica Host.). The comparison was based on measurements of the gas exchange (A/ci, light and temperature response curves), slow and fast chlorophyll fluorescence kinetics, and some growth and leaf parameters. In MG, we observed the highest CO2 assimilation rate [Formula: see text] electron transport rate (Jmax) and maximum carboxylation rate [Formula: see text]. The Aegilops leaves had substantially lower values of all photosynthetic parameters; this fact correlated with its lower biomass production. The mesophyll conductance was almost the same in Aegilops and MG, despite the significant differences in leaf phenotype. In contrary, in LR with a higher dry mass per leaf area, the half mesophyll conductance (gm) values indicated more limited CO2 diffusion. In Aegilops, we found much lower carboxylation capacity; this can be attributed mainly to thin leaves and lower Rubisco activity. The difference in CO2 assimilation rate between MG and others was diminished because of its higher mitochondrial respiration activity indicating more intense metabolism. Assessment of temperature response showed lower temperature optimum and a narrow ecological valence (i.e., the range determining the tolerance limits of a species to an environmental factor) in Aegilops. In addition, analysis of photosynthetic thermostability identified the LR as the most sensitive. Our results support the idea that the selection for high yields was accompanied by the increase of photosynthetic productivity through unintentional improvement of leaf anatomical and biochemical traits including tolerance to non-optimal temperature conditions.

Nasal vaccination stimulates CD8(+) T cells for potent protection against mucosal Brucella melitensis challenge.

Brucellosis remains a significant zoonotic threat worldwide. Humans and animals acquire infection via their oropharynx and upper respiratory tract following oral or aerosol exposure. After mucosal infection, brucellosis develops into a systemic disease. Mucosal vaccination could offer a viable alternative to conventional injection practices to deter disease. Using a nasal vaccination approach, the ΔznuA B. melitensis was found to confer potent protection against pulmonary Brucella challenge, and reduce colonization of spleens and lungs by more than 2500-fold, with >50% of vaccinated mice showing no detectable brucellae. Furthermore, 10-fold more brucellae-specific, interferon-γ (IFN-γ)-producing CD8(+) T cells than CD4(+) T cells were induced in the spleen and respiratory lymph nodes. Evaluation of pulmonary and splenic CD8(+) T cells from mice vaccinated with ΔznuA B. melitensis revealed that these expressed an activated effector memory (CD44(hi)CD62L(lo)CCR7(lo)) T cells producing elevated levels of IFN-γ, tumor necrosis factor-α, perforin and granzyme B. To assess the relative importance of these increased numbers of CD8(+) T cells, CD8(-/-) mice were challenged with virulent B. melitensis, and they showed markedly increased bacterial loads in organs in contrast to similarly challenged CD4(-/-) mice. Only ΔznuA B. melitensis- and Rev-1-vaccinated CD4(-/-) and wild-type mice, not CD8(-/-) mice, were completely protected against Brucella challenge. Determination of cytokines responsible for conferring protection showed the relative importance of IFN-γ, but not interleukin-17 (IL-17). Unlike wild-type (wt) mice, IL-17 was greatly induced in IFN-γ(-/-) mice, but IL-17 could not substitute for IFN-γ's protection, although an increase in brucellae dissemination was observed upon in vivo IL-17 neutralization. These results show that nasal ΔznuA B. melitensis vaccination represents an attractive means to stimulate systemic and mucosal immune protection via CD8(+) T-cell engagement.