Arabidopsis plants expressing only the redox-regulated Rca-α isoform have constrained photosynthesis and plant growth

Different Spatial Configurations of LED Light Sources Enhance Growth in Tomato Seedlings by Influencing Photosynthesis, CO2 Assimilation, and Endogenous Hormones

Sub-optimal light environments in controlled agricultural settings often limit the productivity of plants. While LED supplementary lighting has been widely adopted to mitigate light deficiencies, the spatial arrangement of LED light sources remains a critical but under-explored factor affecting plant physiological responses. In this study, we used the affiliation function method to comprehensively analyze the effects of four spatial LED supplementary lighting configurations-top-down lighting (T1), mid-canopy upward lighting (T2), mid-canopy downward lighting (T3), and bottom-up lighting (T4)-on the growth and photosynthetic performance of tomato plants. Our findings reveal that the T1 treatment significantly increased light absorption in the upper and middle leaves, enhanced photosynthetic efficiency, promoted the CO2 assimilation rate, and elevated the activities of key Calvin cycle enzymes, including ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), fructose-1,6-bisphosphatase (FBPase), transketolase (TK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and fructose-1,6-bisphosphate aldolase (FBA). These changes led to improved carbohydrate metabolism and biomass accumulation. Additionally, the T4 treatment markedly enhanced photosynthetic activity in the lower leaves, increasing sugar metabolism-related enzyme activities, such as sucrose synthase (SS), sucrose phosphate synthase (SPS), acid invertase (AI), and neutral invertase (NI). Consequently, compared with the CK treatment, the T4 treatment significantly increased the accumulation of glucose, fructose, and sucrose, with increases of 47.36%, 27.61%, and 87.21%, respectively. Furthermore, LED supplementation regulated endogenous hormone levels, thereby promoting overall plant growth. This study highlights the importance of the spatial arrangement of LEDs in optimizing light distribution and enhancing plant productivity, providing valuable theoretical and practical insights for improving agricultural practices in controlled environments.

Synergistic role of Rubisco inhibitor release and degradation in photosynthesis

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) exhibits catalytic promiscuity, resulting in error-prone reactions and the formation of inhibitory sugar phosphates. Specifically, Xylulose-1,5-bisphosphate (XuBP) acts as an inhibitor by binding to the active site of Rubisco, thereby impairing its catalytic function. Thermolabile Rubisco activase (Rca) facilitates the release of such inhibitors, including XuBP, by remodelling Rubisco. In Arabidopsis thaliana, the phosphatase pair CbbYA and CbbYB subsequently hydrolyses XuBP to prevent its rebinding to Rubisco. To explore the functional interplay between these components in maintaining photosynthesis, cbbya, cbbyb and cbbyab mutants were crossed with RCA knockdown (rca-2) lines. Additionally, both RCA and CBBYA were overexpressed in wild-type (WT) Arabidopsis thaliana. Phenotypic analyses revealed an exacerbation in decreased growth and photosynthetic efficiency in the cbbyab rca-2 double mutants compared with the control mutants (cbbyab and rca-2), indicating a negative genetic interaction. Furthermore, the co-overexpression of RCA and CBBYA did not improve photosynthesis under short-term heat stress, and light reactions were adversely affected relative to the WT. These findings illustrate the synergistic roles of Rca, CbbYA and CbbYB in maintaining carbon fixation and promoting plant growth in Arabidopsis thaliana. Thus, the coordinated regulation of Rca and CbbY enzymes is crucial for optimizing photosynthetic efficiency.

Rice RuBisCO activase promotes the dark-induced leaf senescence by enhancing the degradation of filamentation temperature-sensitive H

Leaf senescence is a complex process that is triggered by many developmental and environmental factors. However, the mechanisms regulating leaf senescence remain unclear. Here, we revealed that rice ribulose-1,5-bisphosphate carboxylase/oxygenase activase (RCA) promotes the onset of basal dark-induced senescence. RCA was mainly expressed in the leaves, and its expression level quickly declined under dark conditions. Furthermore, rca mutant plants presented a prolonged leaf longevity phenotype in the dark, whereas overexpression of the large isoform of RCA (RCAL), not small isoform (RCAS), in rice and Arabidopsis accelerated leaf senescence. Filamentation temperature-sensitive H (OsFtsH1), a zinc metalloprotease, interacts with RCAL and RCAS and presents a higher binding efficiency to RCAL than RCAS in darkness. Furthermore, we found that RCAL promotes 26S proteasome-mediated degradation of OsFtsH1 protein, which can be inhibited by protease inhibitor MG132. Consequently, OsFtsH1 loss-of-function mutants exhibit accelerated leaf senescence, whereas OsFtsH1-overexpressing plants display delayed senescence. Collectively, our findings highlight the significant role of RCAL isoform in regulating leaf senescence under dark conditions, particularly through enhancing the degradation of OsFtsH1.

Overexpression of the transcription factor ANAC017 results in a genomes uncoupled phenotype under lincomycin

Over-expression (OE) lines for the ER-tethered NAC transcription factor ANAC017 displayed de-repression of gun marker genes when grown on lincomycin (lin). RNA-seq revealed that ANAC017OE2 plants constitutively expressed greater than 40% of the genes induced in wild-type with lin treatment, including plastid encoded genes ycf1.2 and the gene cluster ndhH-ndhA-ndhI-ndhG-ndhE-psaC-ndhD, documented as direct RNA targets of GUN1. Genes encoding components involved in organelle translation were enriched in constitutively expressed genes in ANAC017OE2. ANAC017OE resulted in constitutive location in the nucleus and significant constitutive binding of ANAC017 was detected by ChIP-Seq to target genes. ANAC017OE2 lines maintained the ability to green on lin, were more ABA sensitive, did not show photo-oxidative damage after exposure of de-etiolated seedlings to continuous light and the transcriptome response to lin were as much as 80% unique compared to gun1-1. Both double mutants, gun1-1:ANAC017OE and bzip60:ANAC017OE (but not single bzip60), have a gun molecular gene expression pattern and result in variegated and green plants, suggesting that ANAC017OE may act through an independent pathway compared to gun1. Over-expression of ANAC013 or rcd1 did not produce a GUN phenotype or green plants on lin. Thus, constitutive ANAC017OE2 establishes an alternative transcriptional program that likely acts through a number of pathways, that is, maintains plastid gene expression, and induction of a variety of transcription factors involved in reactive oxygen species metabolism, priming plants for lin tolerance to give a gun phenotype.

Light controls mesophyll-specific post-transcriptional splicing of photoregulatory genes by AtPRMT5

Light plays a central role in plant growth and development, providing an energy source and governing various aspects of plant morphology. Previous study showed that many polyadenylated full-length RNA molecules within the nucleus contain unspliced introns (post-transcriptionally spliced introns, PTS introns), which may play a role in rapidly responding to changes in environmental signals. However, the mechanism underlying post-transcriptional regulation during initial light exposure of young, etiolated seedlings remains elusive. In this study, we used FLEP-seq2, a Nanopore-based sequencing technique, to analyze nuclear RNAs in Arabidopsis (Arabidopsis thaliana) seedlings under different light conditions and found numerous light-responsive PTS introns. We also used single-nucleus RNA sequencing (snRNA-seq) to profile transcripts in single nucleus and investigate the distribution of light-responsive PTS introns across distinct cell types. We established that light-induced PTS introns are predominant in mesophyll cells during seedling de-etiolation following exposure of etiolated seedlings to light. We further demonstrated the involvement of the splicing-related factor A. thaliana PROTEIN ARGININE METHYLTRANSFERASE 5 (AtPRMT5), working in concert with the E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a critical repressor of light signaling pathways. We showed that these two proteins orchestrate light-induced PTS events in mesophyll cells and facilitate chloroplast development, photosynthesis, and morphogenesis in response to ever-changing light conditions. These findings provide crucial insights into the intricate mechanisms underlying plant acclimation to light at the cell-type level.

Maize (Zea mays L.) planted at higher density utilizes dynamic light more efficiently

In nature, plants are exposed to a dynamic light environment. Fluctuations in light decreased the photosynthetic light utilization efficiency (PLUE) of leaves, and much more severely in C4 species than in C3 species. However, little is known about the plasticity of PLUE under dynamic light in C4 species. Present study focused on the influence of planting density to the photosynthesis under dynamic light in maize (Zea mays L.), a most important C4 crop. In addition, the molecular mechanism behind photosynthetic adaptation to planting density were also explored by quantitative proteomics analysis. Results revealed that as planting density increases, maize leaves receive less light that fluctuates more. The maize planted at high density (HD) improved the PLUE under dynamic light, especially in the middle and later growth stages. Quantitative proteomics analysis showed that the transfer of nitrogen from Rubisco to RuBP regeneration and C4 pathway related enzymes contributes to the photosynthetic adaptation to lower and more fluctuating light environment in HD maize. This study provides potential ways to further improve the light energy utilization efficiency of maize in HD.

Application of Isothermal Signal Amplification Technique in the Etiological Diagnosis of Gonorrhea and Drug Resistance Gene Detection

Background: Isothermal signal amplification technique is developed based on the rolling ring amplification mechanism of cyclic DNA molecules in nature. This technique plays an extremely beneficial role in gonorrhea pathogen identification and drug resistance gene detection. Aims: This study analyzes the isothermal signal amplification techniques in the etiological diagnosis of gonorrhea and drug resistance gene detection. Materials and Methods: Urethral, cervical secretion, or prostatic fluid samples from 322 cases of gonorrhea collected from January 2018 to December 2021 at the STD clinic of our hospital dermatology department were selected for direct smear examination and gonococcal culture examination; DNA was extracted from urethral, cervical secretion, or prostatic fluid samples and then used for pathogen identification by SAT assay and rolling loop nucleic acid amplification technique, smear examination and pathogen culture examination methods, SAT assay, and isothermal signal amplification technique for comparative sensitivity and specificity analysis. Results: The highest rate of gonorrhea positivity was for the urine rolling loop nucleic acid amplification technique, followed by the swab rolling loop nucleic acid amplification technique, and the lowest rate of gonorrhea positivity was for the urine SAT test. The difference in the positivity rate between the two urine testing methods was statistically significant (P < 0.05). The highest sensitivity of the urine rolling loop nucleic acid amplification technique method for the detection of gonorrhea pathogens and the lowest sensitivity of the urine SAT method were statistically significant (P < 0.01). The differences in sensitivity and specificity between the swab rolling loop nucleic acid amplification technique and the swab SAT method were not statistically significant (P > 0.05). ROC curves were plotted based on sensitivity and specificity, with swab SAT assay (AUC = 0.998) > rolling loop nucleic acid amplification technique (AUC = 0.981). Comparing the negative rates of urine and swab rolling loop nucleic acid amplification technique and urine SAT assay, the differences were not statistically significant (P > 0.05). Conclusion: The isothermal signal amplification technique improves the shortcomings of gonorrhea pathogen identification means and drug resistance gene detection methods, with good detection sensitivity and specificity, simple operation, low price, and easy promotion, which has obvious advantages in clinical applications and epidemiological studies.

Redox regulation of NADP-malate dehydrogenase is vital for land plants under fluctuating light environment

Many enzymes involved in photosynthesis possess highly conserved cysteine residues that serve as redox switches in chloroplasts. These redox switches function to activate or deactivate enzymes during light-dark transitions and have the function of fine-tuning their activities according to the intensity of light. Accordingly, many studies on chloroplast redox regulation have been conducted under the hypothesis that "fine regulation of the activities of these enzymes is crucial for efficient photosynthesis." However, the impact of the regulatory system on plant metabolism is still unclear. To test this hypothesis, we here studied the impact of the ablation of a redox switch in chloroplast NADP-malate dehydrogenase (MDH). By genome editing, we generated a mutant plant whose MDH lacks one of its redox switches and is active even in dark conditions. Although NADPH consumption by MDH in the dark is expected to be harmful to plant growth, the mutant line did not show any phenotypic differences under standard long-day conditions. In contrast, the mutant line showed severe growth retardation under short-day or fluctuating light conditions. These results indicate that thiol-switch redox regulation of MDH activity is crucial for maintaining NADPH homeostasis in chloroplasts under these conditions.