Physiological and proteomics responses of nitrogen assimilation and glutamine/glutamine family of amino acids metabolism in mulberry (Morus alba L.) leaves to NaCl and NaHCO3 stress

SlGAD2 is the target of SlTHM27, positively regulates cold tolerance by mediating anthocyanin biosynthesis in tomato

Cold stress significantly limits the yield and quality of tomato. Deciphering the key genes related to cold tolerance is important for selecting and breeding superior cold-tolerant varieties. γ-aminobutyric acid (GABA) responds to various types of stress by rapidly accumulating in plant. In this study, glutamic acid decarboxylase (GAD2) was a positive regulator to enhance cold stress tolerance of tomato. Overexpression of SlGAD2 decreased the extent of cytoplasmic membrane damage and increased the endogenous GABA content, antioxidant enzyme activities, and reactive oxygen species (ROS) scavenging capacity in response to cold stress, whereas Slgad2 mutant plants showed the opposite trend. In addition, SlGAD2 induced anthocyanin biosynthesis in response to cold stress by increasing the content of endogenous GABA. Further study revealed that SlGAD2 expression was negatively regulated by the transcription factor SlTHM27. However, the transcript levels of SlTHM27 were repressed under cold stress. Antioxidant enzyme activities, SlGAD2 transcript levels, GABA and anthocyanin contents were significantly increased in Slthm27 mutant plants. Further, our study demonstrated that SlTHM27 decreases SlGAD2-promoted cold resistance in tomato by repressing SlGAD2 transcription. Overall, our results showed that the SlTHM27-SlGAD2 model regulates the cold tolerance in tomato by regulating GABA and anthocyanin.

Comprehensive analysis of the aldehyde dehydrogenase gene family in Phaseolus vulgaris L. and their response to saline-alkali stress

Background

Aldehyde dehydrogenase (ALDH) scavenges toxic aldehyde molecules by catalyzing the oxidation of aldehydes to carboxylic acids. Although ALDH gene family members in various plants have been extensively studied and were found to regulate plant response to abiotic stress, reports on ALDH genes in the common bean (Phaseolus vulgaris L.) are limited. In this study, we aimed to investigate the effects of neutral (NS) and basic alkaline (AS) stresses on growth, physiological and biochemical indices, and ALDH activity, ALDH gene expression of common bean. In addition, We used bioinformatics techniques to analyze the physical and chemical properties, phylogenetic relationships, gene replication, collinearity, cis-acting elements, gene structure, motifs, and protein structural characteristics of PvALDH family members.

Results

We found that both NS and AS stresses weakened the photosynthetic performance of the leaves, induced oxidative stress, inhibited common bean growth, and enhanced the antioxidative system to scavenge reactive oxygen species. Furthermore, we our findings revealed that ALDH in the common bean actively responds to NS or AS stress by inducing the expression of PvALDH genes. In addition, using the established classification criteria and phylogenetic analysis, 27 PvALDHs were identified in the common bean genome, belonging to 10 ALDH families. The primary expansion mode of PvALDH genes was segmental duplication. Cis-acting elemental analysis showed that PvALDHs were associated with abiotic stress and phytohormonal responses. Gene expression analysis revealed that the PvALDH gene expression was tissue-specific. For instance, PvALDH3F1 and PvALDH3H1 were highly expressed in flower buds and flowers, respectively, whereas PvALDH3H2 and PvALDH2B4 were highly expressed in green mature pods and young pods, respectively. PvALDH22A1 and PvALDH11A2 were highly expressed in leaves and young trifoliates, respectively; PvALDH18B2 and PvALDH18B3 were highly expressed in stems and nodules, respectively; and PvALDH2C2 and PvALDH2C3 were highly expressed in the roots. PvALDHs expression in the roots responded positively to NS-AS stress, and PvALDH2C3, PvALDH5F1, and PvALDH10A1 were significantly (P < 0.05) upregulated in the roots.

Conclusion

These results indicate that AS stress causes higher levels of oxidative damage than NS stress, resulting in weaker photosynthetic performance and more significant inhibition of common bean growth. The influence of PvALDHs potentially modulates abiotic stress response, particularly in the context of saline-alkali stress. These findings establish a basis for future research into the potential roles of ALDHs in the common bean.

Physiological responses and molecular mechanism of Chlorella sorokiniana to surgical mask exudates in wastewater

Microalgae-based bioremediation is likely to be challenged by the microplastics (MPs) in wastewater induced by the widely use of surgical masks (SMs) during COVID-19. However, such toxic impact was generally evaluated under high exposure concentrations of MPs, which was not in agreement with the actual wastewater environments. Therefore, this study investigated the microalgal cellular responses to the surgical mask exudates (SMEs) in wastewater and explored the underlying inhibitory mechanism from the molecular perspective. Specifically, 390 items/L SMEs (including 200 items/L MPs which was the actual MP level in wastewater) significantly inhibited nutrient uptake and photosynthetic activities interrupted peroxisome biogenesis and induced oxidative stress which destroyed the structure of cell membrane. Moreover, the SMEs exposure also affected carbon fixation pathways, suppressed ABC transporters while promoted oxidative phosphorylation processes for the ATP accumulation These comprehensive processes led to an 8.5% reduced microalgae growth and variations of cellular biocomponents including lipid, carbohydrate, and protein. The increased carotenoids and consumed unsaturated fatty acid were considered to alleviate the SMEs-induced stress, and the enhanced EPS secretion facilitated the homogeneous aggregation. These findings will enhance current understandings of the SMEs effects in wastewater on microalgae and further improve the practical relevance of microalgae wastewater bioremediation technology.

Quantification of Glucose Metabolism and Nitrogen Utilization in Two Brassicaceae Species under Bicarbonate and Variable Ammonium Soil Conditions

In karst habitats under drought conditions, high bicarbonate (high pH), and an abundant nitrate soil environment, bicarbonate regulates the glycolysis (EMP) and pentose phosphate pathways (PPP), which distribute ATP and NADPH, affecting nitrate (NO3-) and ammonium (NH4+) utilization in plants. However, the relationship between EMP PPP and NO3-, and NH4+ utilization and their responses to bicarbonate and variable ammonium still remains elusive. In this study, we used Brassica napus (Bn, a non-karst-adaptable plant) and Orychophragmus violaceus (Ov, a karst-adaptable plant) as plant materials, employed a bidirectional nitrogen-isotope-tracing method, and performed the quantification of the contribution of EMP and PPP. We found that bicarbonate and ammonium inhibited glucose metabolism and nitrogen utilization in Bn under simulated karst habitats. On the other hand, it resulted in a shift from EMP to PPP to promote ammonium utilization in Ov under high ammonium stress in karst habitats. Compared with Bn, bicarbonate promoted glucose metabolism and nitrogen utilization in Ov at low ammonium levels, leading to an increase in photosynthesis, the PPP, carbon and nitrogen metabolizing enzyme activities, nitrate/ammonium utilization, and total inorganic nitrogen assimilation capacity. Moreover, bicarbonate significantly reduced the growth inhibition of Ov by high ammonium, resulting in an improved PPP, RCRUBP, and ammonium utilization to maintain growth. Quantifying the relationships between EMP, PPP, NO3-, and NH4+ utilization can aid the accurate analysis of carbon and nitrogen use efficiency changes in plant species. Therefore, it provides a new prospect to optimize the nitrate/ammonium utilization in plants and further reveals the differential responses of inorganic carbon and nitrogen (C-N) metabolism to bicarbonate and variable ammonium in karst habitats.

Mechanistic investigation of enhanced bacterial soft rot resistance in lettuce (Lactuca sativa L.) with elemental sulfur nanomaterials

Crop diseases significantly threaten global food security and will worsen with a changing climate. Elemental sulfur nanomaterials (S NMs) were used to suppress bacterial pathogen Pectobacterium carotovorum on lettuce (Lactuca sativa L.). Foliar application with S NMs at 10-100 mg/L statistically decreased the occurrence of bacterial soft rot, where 100 mg/L exhibited the best performance with alleviating disease severity by 94.1 % as relative to infected controls. The disease suppression efficiency of S based materials (100 mg/L) and a conventional pesticide (thiophanate-methyl) followed the order of S NMs ≈ pesticide > S bulk particles (BPs) > sulfate. The disease control efficiency of S NMs was 1.33- and 3.20-fold that of S BPs and sulfate, respectively, and the shoot and root biomass with S NMs was 1.25- and 1.17-fold that of the pesticide treated plants. Mechanistically, S NMs (1) triggered jasmonic acid (JA) and salicylic acid (SA) mediated systematic induced resistance and systemic acquired resistance, thereby upregulating pathogenesis-related gene expression (enhanced by 29.3-259.7 %); (2) enhanced antioxidative enzyme activity and antioxidative gene expression (improved by 67.5-326.6 %), thereby alleviating the oxidative stress; and (3) exhibited direct in vivo antibacterial activity. Metabolomics analysis demonstrated that S NMs also promoted the tricarboxylic acid cycle and increased SA and JA metabolite biosynthesis. Moreover, S NMs application increased nutritive quality of lettuce by 20.8-191.7 %. These findings demonstrate that S NMs have potential to manage crop disease, thereby reducing the environmental burden due to decreasing use of conventional pesticides.

Sustaining nitrogen dynamics: A critical aspect for improving salt tolerance in plants

In the current changing environment, salt stress has become a major concern for plant growth and food production worldwide. Understanding the mechanisms of how plants function in saline environments is critical for initiating efforts to mitigate the detrimental effects of salt stress. Agricultural productivity is linked to nutrient availability, and it is expected that the judicious metabolism of mineral nutrients has a positive impact on alleviating salt-induced losses in crop plants. Nitrogen (N) is a macronutrient that contributes significantly to sustainable agriculture by maintaining productivity and plant growth in both optimal and stressful environments. Significant progress has been made in comprehending the fundamental physiological and molecular mechanisms associated with N-mediated plant responses to salt stress. This review provided an (a) overview of N-sensing, transportation, and assimilation in plants; (b) assess the salt stress-mediated regulation of N dynamics and nitrogen use- efficiency; (c) critically appraise the role of N in plants exposed to salt stress. Furthermore, the existing but less explored crosstalk between N and phytohormones has been discussed that may be utilized to gain a better understanding of plant adaptive responses to salt stress. In addition, the shade of a small beam of light on the manipulation of N dynamics through genetic engineering with an aim of developing salt-tolerant plants is also highlighted.

The Δ1-pyrroline-5-carboxylate synthetase family performs diverse physiological functions in stress responses in pear (Pyrus betulifolia)

Δ1-Pyrroline-5-carboxylate synthetase (P5CS) acts as the rate-limiting enzyme in the biosynthesis of proline in plants. Although P5CS plays an essential role in plant responses to environmental stresses, its biological functions remain largely unclear in pear (Pyrus betulifolia). In the present study, 11 putative pear P5CSs (PbP5CSs) were identified by comprehensive bioinformatics analysis and classified into five subfamilies. Segmental and tandem duplications contributed to the expansion and evolution of the PbP5CS gene family. Various cis-acting elements associated with plant development, hormone responses, and/or stress responses were identified in the promoters of PbP5CS genes. To investigate the regulatory roles of PbP5CS genes in response to abiotic and biotic stresses, gene expression patterns in publicly available data were explored. The tissue-specific expressional dynamics of PbP5CS genes indicate potentially important roles in pear growth and development. Their spatiotemporal expression patterns suggest key functions in multiple environmental stress responses. Transcriptome and real-time quantitative PCR analyses revealed that most PbP5CS genes exhibited distinct expression patterns in response to drought, waterlogging, salinity-alkalinity, heat, cold, and infection by Alternaria alternate and Gymnosporangium haraeanum. The results provide insight into the versatile functions of the PbP5CS gene family in stress responses. The findings may assist further exploration of the physiological functions of PbP5CS genes for the development and enhancement of stress tolerance in pear and other fruits.

The source, level, and balance of nitrogen during the somatic embryogenesis process drive cellular differentiation

Since the discovery of somatic embryogenesis (SE), it has been evident that nitrogen (N) metabolism is essential during morphogenesis and cell differentiation. Usually, N is supplied to cultures in vitro in three forms, ammonium (NH₄⁺), nitrate (NO₃^-), and amino N from amino acids (AAs). Although most plants prefer NO₃^- to NH₄⁺, NH₄⁺ is the primary form route to be assimilated. The balance of NO₃^- and NH₄⁺ determines if the morphological differentiation process will produce embryos. That the N reduction of NO₃^- is needed for both embryo initiation and maturation is well-established in several models, such as carrot, tobacco, and rose. It is clear that N is indispensable for SE, but the mechanism that triggers the signal for embryo formation remains unknown. Here, we discuss recent studies that suggest an optimal endogenous concentration of auxin and cytokinin is closely related to N supply to plant tissue. From a molecular and biochemical perspective, we explain N's role in embryo formation, hypothesizing possible mechanisms that allow cellular differentiation by changing the nitrogen source.

Biotinylated subunit of 3-methylcrotonyl-CoA carboxylase encoding gene (AtMCCA) participating in Arabidopsis resistance to carbonate Stress by transcriptome analysis

Soil salinization is a major factor impacting modern agricultural production, and alkaline soils contain large amounts of NaHCO₃. Therefore, understanding plant tolerance to high levels of NaHCO₃ is essential. In this study, a transcriptome analysis of shoot and root tissues of wild-type Arabidopsis thaliana was conducted at 0, 4, 12, 24 and 48 h after exposure to a 3 mM NaHCO₃ stress. We focused on differentially expressed genes (DEGs) in roots identified in the early stages (4 h and 12 h) of the NaHCO₃ stress response that were enriched in GO term, carboxylic acid metabolic process, and utilize HCO₃^-. Six genes were identified that exhibited similar expression patterns in both the RNA-seq and qRT-PCR data. We also characterized the phenotypic response of AtMCCA-overexpressing plants to carbonate stress, and found that the ability of AtMCCA-overexpressing plants to tolerate carbonate stress was enhanced by the addition of biotin to the growth medium.

Comparative Proteomics of Mulberry Leaves at Different Developmental Stages Identify Novel Proteins Function Related to Photosynthesis

Mulberry leaves at different positions are different in photosynthetic rate, nutrient substance and feeding impact to silkworms. Here, we investigated the proteomic differences of the first (L1), sixth (L6), and twentieth (L20) mulberry leaves at different stem positions (from top to the base) using a label-free quantitative proteomics approach. L1 contained less developed photosynthetic apparatus but was more active in protein synthesis. L20 has more channel proteins and oxidoreductases relative to L6. Proteins that detected in all measured leaves were classified into three groups according to their expression patterns in L1, L6, and L20. The protein group that displayed the maximum amount in L6 has the highest possibility that function related to photosynthesis. Nine function unknown proteins belong to this group were further analyzed in the light responsive expression, evolutionary tree and sub-cellular localization analysis. Based on the results, five proteins were suggested to be involved in photosynthesis. Taken together, these results reveal the molecular details of different roles of mulberry leaves at different developmental stages and contribute to the identification of five proteins that might function related to photosynthesis.

Physiological and comparative transcriptome analysis of leaf response and physiological adaption to saline alkali stress across pH values in alfalfa (Medicago sativa)

Soil salinization is a critical factor limiting growth and causing physiological dysfunction in plants. The damage from alkaline salt in most plants is significantly greater than that from neutral salt. However, there is still a lack of research on the action mechanism by which saline alkali stress on plants under the same salt concentration across different pH values. The present study examined the effects of different pH values (7.0, 8.0, 9.0, and 10.0) under the same salt concentration (200 mmolL^-1) on photosynthetic function, photoprotective mechanism, nitrogen metabolism, and osmotic regulation in alfalfa (Medicago sativa) leaves, including a transcriptomic analysis of changes in gene expression related to the above metabolic processes. The results showed that low pH saline alkali stress (pH 7.0 and 8.0) promoted chlorophyll synthesis in alfalfa leaves, and non-photochemical quenching (NPQ) and cyclic electron transfer (CEF) were promoted. There was no significant effect on plant growth or photochemical activity. The soluble sugar, proline, and soluble protein contents did not change significantly, and there was no obvious oxidative damage in alfalfa leaves. However, when pH increased to 9.0 and 10.0, KEGG enrichment analysis showed that photosynthesis (map00195) and nitrogen metabolism (map00910) were significantly enriched (P < 0.05), and PSII antenna protein coding genes were down-regulated under pH 9.0 and 10.0 treatments. The activities of PSII and PSI were decreased under high pH saline alkali stress, and the expression levels of the photosynthetic electron transporter-related genes PetA, PetB, petE, and petF were also significantly down-regulated. PSII was more sensitive to high pH saline alkali stress than PSI, and the PSII receptor side was more sensitive to high pH saline alkali stress than the PSII donor side. The activities of the oxygen-evolving complex (OEC) and PSI were significantly damaged only at pH 10.0. The activities of nitrate reductase (NR) and nitrite reductase (NiR), the expression levels of their genes, and the content of soluble protein were also decreased under pH 9.0 and 10.0 treatments. The inhibition of plant growth and oxidative damage to alfalfa leaves caused by high pH saline alkali stress were mainly related to the inhibition of photosynthesis (light energy absorption, electron transfer) and nitrogen metabolism (NO₃^- reduction). Under high pH saline alkali stress (pH 10.0), the photoprotection mechanisms such as CEF and NPQ were inhibited, which was also one of the important reasons for photoinhibition in alfalfa leaves. The accumulation of osmotic adjustment substances, such as soluble sugar and proline, was an important mechanism by which alfalfa physiologically adapted to high pH alkaline salt stress.