Comprehensive study of the genes involved in chlorophyll synthesis and degradation pathways in some monocot and dicot plant species

Differential Gene Expression Responses to Salt and Drought Stress in Tall Fescue (Festuca arundinacea Schreb.)

Understanding gene expression kinetics and the underlying physiological mechanisms in stress combinations is a challenge for the purpose of stress resistance breeding. The novelty of this study is correlating the physiological mechanisms with the expression of key target genes in tall fescue under a combination of various salinity and osmotic stress treatments. Four drought- and salt-responsive genes belonging to different crucial pathways evaluated included one transcription factor FabZIP69, one for the cytosolic polyamine synthetase FaADC1, one for ABA signaling FaCYP707A1, and another one for the specific Na+/H+ plasma membrane antiporter FaSOS1 involve in osmotic homeostasis. FaSOS1, FaCYP707A1, and FabZIP69 were induced early at 6 h after NaCl treatment, while FaSOS1 and FaCYP707A1 were transcribed gradually after exposure to PEG. However, stress interactions showed a significantly increased expression in all genes. Expression of these genes was positively correlated to Pro, SSs, IL, DPPH, and antioxidant enzyme activity and negatively correlated with RWC, total Chl, and MSI. Chemical analyses showed that tall fescue plants exposed to the combination of stresses exhibited increased quantity of reactive oxygen species (H2O2), EL and DPPH, and higher levels of antioxidant enzyme activities (CAT, and SOD), Pro, and SSs content, compared with control seedlings. Under dual-stress conditions, the expression of FabZIP69 was effective in controlling the expression of FaSOS1 and FaADC1 genes differently.

Comprehensive Analysis of the Yield and Leaf Quality of Fresh Tea (Camellia sinensis cv. Jin Xuan) under Different Nitrogen Fertilization Levels

Reasonable application of nitrogen fertilizer can improve the yield and quality of tea. This study used Jin Xuan as the tested variety and applied nitrogen fertilizer at rates of 0 kg/ha (N0), 150 kg/ha (N150), 300 kg/ha (N300), and 450 kg/ha (N450) in the summer and autumn seasons to analyze the effects of nitrogen application on the quality components and gene expression of tea leaves. The results showed that the N150 treatment significantly increased total polyphenols (TP), total catechins (TC), and caffeine contents, with the most significant increase observed in the content of six monomers of catechins (EGCG, ECG, EGC, GCG, GC, and EC) in the summer. The N300 treatment significantly increased TP and AA contents in the autumn while decreasing TC content. Additionally, the N300 treatment significantly increased caffeine and theanine contents in the autumn. Notably, the N300 treatment significantly increased both summer and autumn tea yields. Multivariate statistical analysis showed that TPs, AAs, TCs, EGC, and caffeine were key factors affecting the quality of Jin Xuan. Furthermore, the N150 treatment upregulated the expression of the phenylalanine ammonia-lyase (PAL) gene, which may increase the accumulation of catechins. In conclusion, it is recommended to apply 150 kg/ha of nitrogen fertilizer in the summer and 300 kg/ha of nitrogen fertilizer in the autumn. This recommendation provides a theoretical basis for improving the quality and yield of tea leaves in summer and autumn.

Comparative Physiology and Transcriptome Analysis Provides Insights into the Regulatory Mechanism of Albinotic Bambusa oldhamii

Albinism is a unique problem encountered in tissue culture experiments, but the underlying mechanism remains unclear in most bamboo species. In this study, we identified the putative regulatory genes in an albino mutant of Bambusa oldhamii using comparative physiology and transcriptome analysis. The degeneration of chloroplasts, low chlorophyll (Chl) content and reduced photosynthetic capacity were observed in albinotic B. oldhamii compared to normal lines. A total of 6191 unigenes were identified that were clearly differentially expressed between albino and normal lines by transcriptome sequencing. Most genes related to chloroplast development (such as Psa, Psb) and pigment biosynthesis (such as LHC, GUN4, ZEP) were downregulated significantly in albinotic lines, which might be responsible for the albino phenotype. Moreover, some transcription factors (TFs) such as PIF and GLK1 were identified to be involved in chloroplast development and Chl synthesis, indicating the involvement of putative regulatory pathways PIF-LHC and GLK1-LHC/Psa/Psb in albinotic B. oldhamii. Finally, the downregulation of some stress responsive TFs (like ICE1 and EREB1) suggested a reduction in stress resistance of albinotic B. oldhamii. The above findings provided new insights into the molecular mechanism of albinism in bamboo.

Morphological and physiological adaptation characteristics of lithophytic bryophytes to karst high calcium environment

BACKGROUND

Lithophytic bryophytes grow on the rock surface, change the habitat on the rock surface through biological karstification, and provide a material basis for the growth of other plants. However, the surface calcium content of bare rock is high. The lithophytic bryophytes may have a special mechanism to adapt to the karst high calcium environment. The present study aimed to explore the physiological regulation process of karst lithophytic bryophytes under high calcium environment, and to provide scientific basis for revealing the maintenance mechanism of karst biodiversity.

RESULTS

With the increase of Ca²⁺ concentration, the contents of Pro, SP and MDA of lithophytic bryophytes showed a downward-upward-downward trend. However, when Ca²⁺ ≥ 400 mmol/L, the contents of Pro and SP changed significantly at 1d, 2d, 3d, 5d and 7d with the extension of culture time, and lithophytic bryophytes died after 2 months of culture. Under different Ca²⁺ concentrations, the maximum SOD activity of lithophytic bryophytes is 1758.00 (U/g FW), the minimum is 92.60 (U/g FW), the maximum POD activity is 120.88 (U/g FW), and the minimum is 4.80 (U/g FW). The antioxidative activity of of Hyophila involuta are higher than that of Didymodon constrictus and Eurohypnum leptothallum, and its enzyme activity changed significantly with the increase of calcium concentration and time.At the same time, the contents of TChl, Chla, and Chlb in lithophytic bryophytes decreased with the increase of Ca²⁺ concentration. When Ca²⁺ = 400 mmol/L, the contents of TChl and Chla were the lowest, but when Ca²⁺ > 400 mmol/L, they began to increase. In addition, ABA is negatively correlated with TChl and Chla, and positively correlated with ROS. It shows that ABA has a certain role in regulating the adaptation of lithophytic bryophytes to high calcium environment.

CONCLUSIONS

Lithophytic bryophytes have strong calcium tolerance, and their physiological response to high calcium stress is different from vascular bundle plants. The general stress principle is not applicable to lithophytic bryophytes. The response of lithophytic bryophytes to the change of Ca²⁺concentration is slow, showing passive response or inert response.

Endophytic bacteria perform better than endophytic fungi in improving plant growth under drought stress: A meta-comparison spanning 12 years (2010-2021)

Drought stress is a serious issue that affects agricultural productivity all around the world. Several researchers have reported using plant growth-promoting endophytic bacteria to enhance the drought resistance of crops. However, how endophytic bacteria and endophytic fungi are effectively stimulating plant growth under drought stress is still largely unknown. In this article, a global meta-analysis was undertaken to compare the plant growth-promoting effects of bacterial and fungal endophytes and to identify the processes by which both types of endophytes stimulate plant growth under drought stress. Moreover, this meta-analysis enlightens how plant growth promotion varies across crop types (C3 vs. C4 and monocot vs. dicot), experiment types (in vitro vs. pots vs. field), and the inoculation methods (seed vs. seedling). Specifically, this research included 75 peer-reviewed publications, 170 experiments, 20 distinct bacterial genera, and eight fungal classes. On average, both endophytic bacterial and fungal inoculation increased plant dry and fresh biomass under drought stress. The effect of endophytic bacterial inoculation on plant dry biomass, shoot dry biomass, root length, photosynthetic rate, leaf area, and gibberellins productions were at least two times greater than that of fungal inoculation. In addition, under drought stress, bacterial inoculation increased the proline content of C4 plants. Overall, the findings of this meta-analysis indicate that both endophytic bacterial and fungal inoculation of plants is beneficial under drought conditions, but the extent of benefit is higher with endophytic bacteria inoculation but it varies across crop type, experiment type, and inoculation method.

Virtual screening and docking analysis of novel ligands for selective enhancement of tea (Camellia sinensis) flavonoids

•

Tea-specific flavonoid biosynthetic pathway (FBP) was retrieved from KEGG.

•

Putative ligands were predicted to enhance enzymes-substrate binding affinity.

•

FBP genes showed moderately higher expression & relatively strong codon adaptation.

•

Most of the genes were AT-rich and biased to A/U-ending synonymous codons.

•

Mutational selection was determining the selective constraints on codon bias.

Flavour of tea is mainly contributed by a group of polyphenols – flavonoids. However, the content of flavonoid fluctuates seasonally and is found to be higher in the first flush of tea, when compared to the second flush. This disparity in the flavonoid content, and hence taste, incurs heavy economic losses to the tea plantation industry each harvest season. For our present study, four key product-specific enzymes (PAL, FNS, FLS and ANS) of the tea-specific flavonoid pathway were selected to perform molecular docking studies with specific virtually screened allosteric modulators. Results of docking analyses showed Naringenin, 2-Morpholin-4-ium-4-ylethanesulfonate, 6-C-Glucosylquercetin, 2-Oxoglutaric acid, 3,5,7,3′,4′-pentahydroxyflavone to be capable of improving the spontaneity of the enzyme-substrate reactions in terms of docking score, RMSD values, and non-covalent interactions (H-bond,hydrophobic interaction, Π-stacking, salt bridge, etc.). Further, the evolutionary relationship of tea flavonoid pathway enzymes was constructed and compared with related taxa. The codon usage-based of tea flavonoid biosynthetic genes indicated the non-biasness of their nucleotide composition. Overall this study will provide a direction towards putative ligand-dependent enhancement of flavonoid content, irrespective of seasonal variation.

Effects of Long-Term Nitrogen Fertilization on the Formation of Metabolites Related to Tea Quality in Subtropical China

As a main agronomic intervention in tea cultivation, nitrogen (N) application is useful to improve tea yield and quality. However, the effects of N application on the formation of tea quality-related metabolites have not been fully studied, especially in long-term field trials. In this study, a 10-year field experiment was conducted to investigate the effect of long-term N application treatments on tea quality-related metabolites, their precursors, and related gene expression. Long-term N application up-regulated the expression of key genes for chlorophyll synthesis and promoted its synthesis, thus increasing tea yield. It also significantly increased the contents of total free amino acids, especially l-theanine, in fresh tea leaves, while decreasing the catechin content, which is conducive to enhancing tea liquor freshness. However, long-term N application significantly reduced the contents of benzyl alcohol and 2-phenylethanol in fresh tea leaves, and also reduced (E)-nerolidol and indole in withered leaves, which were not conducive to the formation of floral and fruity aroma compounds. In general, an appropriate amount of N fertilizer (225 kg/hm²) balanced tea yield and quality. These results not only provide essential information on how N application affects tea quality, but also provide detailed experimental data for field fertilization.