Genome-Wide Identification and Abiotic Stress Expression Analysis of CKX and IPT Family Genes in Cucumber (Cucumis sativus L.).

Cytokinins (CKs) are among the hormones that regulate plants' growth and development, and the CKX and IPT genes, which are CK degradation and biosynthesis genes, respectively, play important roles in fine-tuning plants' cytokinin levels. However, the current research on the function of IPT and CKX in cucumber's growth, development, and response to abiotic stress is not specific enough, and their regulatory mechanisms are still unclear. In this study, we focused on the IPT and CKX genes in cucumber, analyzed the physiological and biochemical properties of their encoded proteins, and explored their expression patterns in different tissue parts and under low light, salt stress, and drought stress. Eight CsCKX and eight CsIPT genes were identified from the cucumber genome. We constructed a phylogenetic tree from the amino acid sequences and performed prediction analyses of the cis-acting elements of the CsCKX and CsIPT promoters to determine whether CsCKXs and CsIPTs are responsive to light, abiotic stress, and different hormones. We also performed expression analysis of these genes in different tissues, and we found that CsCKXs and CsIPTs were highly expressed in roots and male flowers. Thus, they are involved in the whole growth and development process of the plant. This paper provides a reference for further research on the biological functions of CsIPT and CsCKX in regulating the growth and development of cucumber and its response to abiotic stress.

Gibberellin-mediated far-red light-induced leaf expansion in cucumber seedlings.

Our experiments explored the effects of far-red (FR) light on cucumber (Cucumis sativus L. 'Zhongnong No. 26') seedling growth. Our results indicated that FR light significantly promoted the growth of cucumber seedlings. Specifically, it promoted the accumulation of shoot biomass and the elongation of internodes and leaves (except the first leaf at the bottom). Further analysis showed that FR light had no effect on the accumulation contents of abscisic acid (ABA) and auxin (IAA) in seedling leaves. Still, it significantly caused the increase of the gibberellin (GA3, GA4, and GA7) contents and the decrease of GA1 content, which suggested that the leaf expansion progress under FR light may be primarily related to GA. Therefore, the cucumber seedling leaf expansion response to GA was evaluated under different light sources. The exogenous spraying of different GA4/7 contents significantly promoted the leaf expansion of cucumber seedlings under white light, while the GA biosynthesis inhibitor paclobutrazol (PAC) significantly promoted the expression of GA hydrolytic genes (GA2ox2 and GA2ox4) and decreased the content of endogenous active GA, which inhibited the leaf expansion induced by FR light. As expected, the combination of exogenous GA4/7 and PAC restored the growth promotion effect of FR light on cucumber seedling leaves. It increased the contents of endogenous active GA (GA1, GA3, GA4, and GA7), and the expression trend in GA synthetic/hydrolytic-related genes was the opposite of that of PAC was applied alone. All of the above results indicated that FR light regulates leaf expansion progress in cucumber seedlings through GA.

The mechanism of melatonin promotion on cucumber seedling growth at different nitrogen levels.

The supply level of exogenous nitrogen has a very important influence on the growth and development of cucumber. Insufficient or excessive nitrogen application will lead to metabolic disorders in the body and affect the formation of yield. Therefore, it is of great scientific and practical significance to explore the corresponding mitigation measures. Melatonin (MT) is a multi-regulatory molecule with pleiotropic effects on plant growth and development. A large number of studies have shown that the appropriate amount of melatonin supplementation is beneficial to plant growth and development by promoting root development, delaying leaf senescence, and improving fruit yield. However, the study of MT function combined with a detailed physiological analysis of nitrogen (N) absorption and metabolism in cucumber plants needs further strengthening. We performed hydroponic tests at different nitrogen levels to determine the metabolic processes associated with the enhanced tolerance to nitrogen in melatonin-treated cucumber (Cucucumis sativus L.) seedlings. Cucumber seedlings were sprayed with 100 µM melatonin or water and treated with different nitrogen in the growth chamber for 7 days. Nitrogen deficiency significantly inhibited seedling growth, and this growth inhibition was partially alleviated by melatonin. The expression analysis of related carbon and nitrogen genes showed that the genes whose expression was significantly altered by melatonin were mainly related to carbon (C) and nitrogen (N) metabolism. By enzyme activity and reactive oxygen content data analysis, melatonin-treated cucumber seedlings showed relatively stable carbon and nitrogen levels compared to untreated ones. In conclusion, MT can repair the impaired growth and development situation by regulating the nitrogen assimilation capacity and the balance between oxidation and oxidative metabolism and carbon metabolism in the cucumber under different nitrogen levels.

A combined proteomics and metabolomics analysis reveals the invisible regulation of plant root responses to oxybenzone (benzophenone-3) stress.

Oxybenzone, an environmental pollutant affecting both agriculture and aquatic ecological integrity, has been demonstrated to act as a physiological and metabolic inhibitor on plants, animals, and microorganisms. Research on oxybenzone in higher plants has focused on the above-ground anatomy (leaves), while research on the under-ground parts (roots) has been neglected. In this study, the changes in plant root protein expression and metabolic pathways under oxybenzone treatment were explored through a combined proteomics and metabolomics analysis. A total of 506 differential proteins and 96 differential metabolites were identified, which were mainly distributed in critical pathways such as those for carbon (C) and nitrogen (N) metabolism, lipid metabolism, and antioxidation. Bioinformatics analysis shows that oxybenzone toxicity is predominantly reflected in alterations to root respiratory homeostasis and the manifestation of damaging reactive oxygen species (ROS) and membrane lipid peroxidation, changes to disease resistance-associated proteins, changes to normal C-flow distribution, and the inhibition of cell absorption and utilization of N sources. Plants respond to oxybenzone stress mainly by reconfiguring the mitochondrial electron-transport-chain to bypass oxidative-damage components; improving the efficiency of the antioxidant system to remove excessively accumulated ROS; promoting the detoxification of harmful membrane lipid peroxides; increasing osmotic adjustment substance (such as proline and raffinose) accumulation; adjusting C flow distribution to produce more nicotinamide adenine dinucleotide phosphate (NADPH) for the glutathione cycle; and accumulating free amino acids to increase plant stress tolerant. Our results are the first to map the changes in the physiological and metabolic regulatory network of higher plant roots under oxybenzone stress.

The analysis of lysine succinylation modification reveals the mechanism of oxybenzone damaging of pakchoi (Brassica rapa L. ssp. chinensis).

Oxybenzone (OBZ), one of a broad spectrum of ultraviolet (UV) absorbents, has been proven to be harmful to both plants and animals, while omics analysis of big data at the molecular level is still lacking. Lysine succinylation (Ksuc) is an important posttranslational modification of proteins that plays a crucial role in regulating the metabolic network in organisms under stress. Here, we report the changes in intracellular Ksuc modification in plants under OBZ stress. A total of 1276 succinylated sites on 507 proteins were identified. Among these sites, 181 modified proteins were hypersulfinylated/succinylated in OBZ-stressed pakchoi leaves. Differentially succinylated proteins (DSPs) are distributed mainly in the chloroplast, cytoplasm, and mitochondria and are distributed mainly in primary metabolic pathways, such as reactive oxygen species (ROS) scavenging, stress resistance, energy generation and transfer, photosynthetic carbon fixation, glycolysis, and the tricarboxylic acid (TCA) cycle. Comprehensive analysis shows that Ksuc mainly changes the carbon flow distribution, enhances the activity of the antioxidant system, affects the biosynthesis of amino acids, and increases the modification of histones. The results of this study first showed the profiling of the Kusc map under OBZ treatment and proposed the adaptive mechanism of pakchoi in response to pollutants and other abiotic stresses at the posttranslational level, which revealed the importance of Ksuc in the regulation of various life activities and provides a reference dataset for future research on molecular function.

Effect of Nickel Ions on the Physiological and Transcriptional Responses to Carbon and Nitrogen Metabolism in Tomato Roots under Low Nitrogen Levels.

Nickel (Ni) is an essential trace element for plant growth and a component of the plant body that has many different functions in plants. Although it has been confirmed that nickel ions (Ni2+) havea certain regulatory effect on nitrogen (N) metabolism, there are not enough data to prove whether exogenous Ni2+ can increase the carbon (C) and N metabolism in the roots of tomato seedlingsunder low-nitrogen (LN) conditions. Therefore, through the present experiment, we revealed the key mechanism of Ni2+-mediated tomato root tolerance to LN levels. Tomato plants were cultured at two different N levels (7.66 and 0.383 mmol L-1) and two different Ni2+ levels (0 and 0.1 mg L-1 NiSO4 6H2O) under hydroponic conditions. After nine days, we collected roots for physiological, biochemical, and transcriptome sequencing analyses and found that the activities of N assimilation-related enzymes decreased at LN levels. In contrast, Ni2+ significantly increased the activities of N assimilation-related enzymes and increased the contents of nitrate (NO3-), ammonium (NH4+), and total amino acids. Through root transcriptomic analysis, 3738 differentially expressed genes (DEGs) were identified. DEGs related to C and N metabolism were downregulated after LN application. However, after Ni2+ treatment, PK, PDHB, GAPDH, NR, NiR, GS, GOGAT, and other DEGs related to C and N metabolism were significantly upregulated. In conclusion, our results suggest that Ni2+ can regulate the C and N metabolism pathways in tomato roots to alleviate the impact of LN levels.