Exogenous Ca2+ priming can improve peanut photosynthetic carbon fixation and pod yield under early sowing scenarios in the field

Harnessing cold-resilient and calcium-enriched peanut production technology are crucial for high-yielding peanut cultivation in high-latitude areas. However, there is limited field data about how exogenous calcium (Ca2+) application would improve peanut growth resilience during exposure to chilling stress at early sowing (ES). To help address this problem, a two-year field study was conducted to assess the effects of exogenous foliar Ca2+ application on photosynthetic carbon fixation and pod yield in peanuts under different sowing scenarios. We measured plant growth indexes, leaf photosynthetic gas exchange, photosystems activities, and yield in peanuts. It was indicated that ES chilling stress at the peanut seedling stage led to the reduction of Pn, gs, Tr, Ls, WUE, respectively, and the excessive accumulation of non-structural carbohydrates in leaves, which eventually induced a chilling-dependent feedback inhibition of photosynthesis due mainly to weaken growth/sink demand. While exogenous Ca2+ foliar application improved the export of nonstructural carbohydrates, and photosynthetic capacity, meanwhile activated cyclic electron flow, thereby enhancing growth and biomass accumulation in peanut seedlings undergoing ES chilling stress. Furthermore, ES combined with exogenous Ca2+ application can significantly enhance plant chilling resistance and peanut yield ultimately in the field. In summary, the above results demonstrated that exogenous foliar Ca2+ application restored the ES-linked feedback inhibition of photosynthesis, enhancing the growth/sink demand and the yield of peanuts

NaCl Pretreatment Enhances the Low Temperature Tolerance of Tomato Through Photosynthetic Acclimation

Plants often need to withstand multiple types of environmental stresses (e.g., salt and low temperature stress) because of their sessile nature. Although the physiological responses of plants to single stressor have been well-characterized, few studies have evaluated the extent to which pretreatment with non-lethal stressors can maintain the photosynthetic performance of plants in adverse environments (i.e., acclimation-induced cross-tolerance). Here, we studied the effects of sodium chloride (NaCl) pretreatment on the photosynthetic performance of tomato plants exposed to low temperature stress by measuring photosynthetic and chlorophyll fluorescence parameters, stomatal aperture, chloroplast quality, and the expression of stress signaling pathway-related genes. NaCl pretreatment significantly reduced the carbon dioxide assimilation rate, transpiration rate, and stomatal aperture of tomato leaves, but these physiological acclimations could mitigate the adverse effects of subsequent low temperatures compared with non-pretreated tomato plants. The content of photosynthetic pigments decreased and the ultra-microstructure of chloroplasts was damaged under low temperature stress, and the magnitude of these adverse effects was alleviated by NaCl pretreatment. The quantum yield of photosystem I (PSI) and photosystem II (PSII), the quantum yield of regulatory energy dissipation, and non-photochemical energy dissipation owing to donor-side limitation decreased following NaCl treatment; however, the opposite patterns were observed when NaCl-pretreated plants were exposed to low temperature stress. Similar results were obtained for the electron transfer rate of PSI, the electron transfer rate of PSII, and the estimated cyclic electron flow value (CEF). The production of reactive oxygen species induced by low temperature stress was also significantly alleviated by NaCl pretreatment. The expression of ion channel and tubulin-related genes affecting stomatal aperture, chlorophyll synthesis genes, antioxidant enzyme-related genes, and abscisic acid (ABA) and low temperature signaling-related genes was up-regulated in NaCl-pretreated plants under low temperature stress. Our findings indicated that CEF-mediated photoprotection, stomatal movement, the maintenance of chloroplast quality, and ABA and low temperature signaling pathways all play key roles in maintaining the photosynthetic capacity of NaCl-treated tomato plants under low temperature stress

Rif1 maintains telomeres and mediates DNA repair by encasing DNA ends

In yeast, Rif1 is part of the telosome, where it inhibits telomerase and checkpoint signaling at chromosome ends. In mammalian cells, Rif1 is not telomeric, but it suppresses DNA end resection at chromosomal breaks, promoting repair by nonhomologous end joining (NHEJ). Here, we describe crystal structures for the uncharacterized and conserved ∼125-kDa N-terminal domain of Rif1 from Saccharomyces cerevisiae (Rif1-NTD), revealing an α-helical fold shaped like a shepherd's crook. We identify a high-affinity DNA-binding site in the Rif1-NTD that fully encases DNA as a head-to-tail dimer. Engagement of the Rif1-NTD with telomeres proved essential for checkpoint control and telomere length regulation. Unexpectedly, Rif1-NTD also promoted NHEJ at DNA breaks in yeast, revealing a conserved role of Rif1 in DNA repair. We propose that tight associations between the Rif1-NTD and DNA gate access of processing factors to DNA ends, enabling Rif1 to mediate diverse telomere maintenance and DNA repair functions

Structural basis for Rap1-Rif1-Rif2 assembly : insights into budding yeast telomere architecture and functions

Telomeres form the ends of eukaryotic linear chromosomes and are composed of specialized nucleoprotein complexes. They have been the subject of intense investigation over several decades, as telomere dysfunction has been associated with genome instability and the development of cancer. Yeast (Saccharomyces cerevisiae) telomeric DNA is comprised of irregular TG1-3 repeats, bound in a sequence-specific manner by multiple copies of Rap1, forming Rap1 arrays. Together with its telomere binding proteins Rif1 and Rif2, arrays of Rap1, Rif1 and Rif2 form a protective proteinaceous cap that regulates telomere length, modulates Sir-mediated transcriptional silencing, and prevents unwanted DNA-repair events. As a general transcription regulator in budding yeast, about 90% of cellular Rap1 is found in promoters or silencers, whereas Rif1 and Rif2 can only be detected at telomeres. The following questions remain unresolved for the major telomere capping proteins Rap1, Rif1, and Rif2. What determines the exclusive telomeric localization of Rif1 and Rif2, and their absence elsewhere in the genome, given that the association of Rif1 and Rif2 at telomeres is solely dependent on the Rap1 C-terminal domain (Rap1RCT)? What is the molecular basis behind the competition between Rif and Sir proteins at telomeres? How do the telomere-associated proteins Rap1, Rif1, and Rif2 influence telomerase activities? And, of central importance to genome stability, what are the roles of Rif1 and Rif2 in damping DNA repair at telomeres? To address these questions, I determined the structures of Rif2, Rif2-Rap1RCT, Rif1-Rap1RCT, and the outermost Rif1 C-terminal domain, Rif1CTD, using x-ray crystallography. Structural studies, combined with in vitro reconstitution and cellular assays, demonstrated that Rif1 and Rif2 are the long-sought elements that interlink Rap1 units cooperatively. The long- and short-range protein interactions from Rif1 and Rif2, the multimerization module present in Rif1CTD, and the trans interaction between Rap1 and Rif2 provide a network of Rap1-Rif1-Rif2 complexes. This protein network allows the formation of higher-order structures at telomeres. The organizing principle that controls Rap1-Rif1-Rif2 assembly relies on the presence of arrays of Rap1-binding sites, which are exclusively found in telomeric regions. This explains why Rif1 and Rif2 are restricted to telomeric regions, and are not localized to the other ~300 single/double Rap1-binding sites at promoters or silencers within the S. cerevisiae genome. In addition, I was able to provide the molecular basis for Rif1- and Rif2-modulated silencing at telomeres and HMR. Structural studies, combined with in vivo analysis, allowed me to identify the interaction domains within Rif1 (Rif1RBM) and Rif2 (Rif2RBM), which block the transcriptional repressor Sir3 from accessing the common binding cleft on Rap1. Thus, Rif1 and Rif2 directly compete with Sir3 for the RBM binding groove on Rap1. This protein-binding groove therefore enables Rap1 to integrate opposing cues coming from the Sir3 and Rif1/Rif2 RBMs into a composite silencing response. The partially redundant assembly of Rif1 and Rif2 on Rap1 also elucidates the reported synergistic function of Rif1 and Rif2 in modulating transcriptional silencing at telomeres and HMR. In this study, I could demonstrate that the Rif2-mediated anti-checkpoint function is dependent on its telomeric localization through the protein interaction with Rap1. I further identified a novel function of Rif1 as a direct DNA-binding protein for protecting resected telomeres from being accidentally recognized as DNA double-strand breaks. Both in vivo and in vitro studies illustrate the remarkable ability of Rif1 to directly outcompete the yeast RPA complex from single-stranded DNA next to single-/double-stranded DNA junctions. The architecture of Rap1-Rif1-Rif2 assemblies favors Rif1 binding the resected telomeric DNA, once the telomere capping function is compromised. Notably, the structure-function studies of Rif1CTD and the Rif1 N-terminus (Rif1NTD) provide strong evidence for applying the principle of inhibiting checkpoint activation from yeast to human. The work presented here details how the yeast shelterin complex Rap1-Rif1-Rif2 directly influences transcriptional silencing, telomere length regulation, and telomere protection against inadvertent DNA-damage checkpoint activation

Numerical Simulation of Ventilation Performance in Mushroom Solar Greenhouse Design

Numerical simulation is an effective tool for the thermal management of propulsion systems. Moreover, it contributes to the design and performance assessment of solar greenhouses for mushroom ventilation. Because the planning and design of the clustered solar greenhouse are still undiscovered, this study has developed a 3-D mathematical model suitable for a large-scale park of mushroom solar greenhouses based on computational fluid dynamics (CFD) theory. The effects of the orientation arrangement, horizontal spacing, vertical spacing of the cultivation racks, and the building distance between adjacent greenhouses on the ventilation performance were analyzed. The numerical simulation showed good agreement with the experimental measurement. The CFD results indicated that the reasonable layout of cultivation racks in mushroom solar greenhouses is a north-south arrangement. The horizontal spacing of cultivation racks has a significant influence on the wind speed and cooling rate, and the optimal spacing is 0.8 m. The overall height of the cultivation racks has little effect on the ventilation performance. Nevertheless, the vertical spacing between cultivation rack layers has a remarkable effect, and the optimal vertical spacing is 0.29 m. Reducing the building distance between the two adjacent greenhouses within a certain range helps increase the ventilation efficiency, leading to an increase in land utilization in the greenhouse park. The optimal building distance between the adjacent greenhouses is 10 m. The research results can provide theoretical guidance for improving the production quality and land utilization of mushroom facilities

Study of a novel front-roof-back natural ventilation system for Chinese solar greenhouses

A Chinese solar greenhouse (CSG) is a highly efficient and energy-saving horticultural facility. Ventilation is significantly important for crop production in the greenhouse, and the vent configuration is the basis of the greenhouse design. Current CSG ventilation structures mostly include front bottom vents and top vents to create a suitable temperature environment for the normal development of crops. However, the ventilation capacity and efficiency are limited. In the present study, we proposed a comprehensive front bottom + top + back roof (FTB) ventilation configuration. The greenhouse ventilation was investigated during the summer season by means of field testing and simulation, and the performance of three ventilation structures—front bottom + top (FT), front bottom + back roof (FB) and FTB—was compared. The results showed that FTB stabilized the greenhouse temperature for 20 s less time than FT and FB. The cooling rate of FTB showed a 24.84% and 5.52% improvement over FT and FB, respectively, and the average temperature showed a 13.81% and 3.65% decrease, respectively. Moreover, the ventilation performance of the side walls was investigated in order to determine if they might serve as auxiliary structures for FTB ventilation. Nevertheless, the improvements of cooling rate, wind speed and average temperature were only 0.52%, 2.09% and 0.11%, respectively. The results demonstrated that the novel FTB ventilation proposed in the present study significantly improved ventilation efficiency and uniformity compared with conventional ventilation structures. The results presented herein provide theoretical support for the use and design of greenhouses suitable for China's special climate

Integrated Physiological, Transcriptomic, and Proteomic Analyses Reveal the Regulatory Role of Melatonin in Tomato Plants’ Response to Low Night Temperature

Melatonin is a direct free radical scavenger that has been demonstrated to increase plants’ resistance to a variety of stressors. Here, we sought to examine the effect of melatonin on tomato seedlings subjected to low night temperatures using an integrated physiological, transcriptomic, and proteomic approach. We found that a pretreatment with 100 μM melatonin increased photosynthetic and transpiration rates, stomatal apertures, and peroxidase activity, and reduced chloroplast damage of the tomato plant under a low night temperature. The melatonin pretreatment reduced the photoinhibition of photosystem I by regulating the balance of both donor- and acceptor-side restriction of PSI and by increasing electron transport. Furthermore, the melatonin pretreatment improved the photosynthetic performance of proton gradient regulation 5 (SlPGR5) and SlPGR5-like photosynthetic phenotype 1 (SlPGRL1)-suppressed transformants under a low night temperature stress. Transcriptomic and proteomic analyses found that the melatonin pretreatment resulted in the upregulation of genes and proteins related to transcription factors, signal transduction, environmental adaptation, and chloroplast integrity maintenance in low night temperature-stressed tomato plants. Collectively, our results suggest that melatonin can effectively improve the photosynthetic efficiency of tomato plants under a low night temperature and provide novel insights into the molecular mechanism of melatonin-mediated abiotic stress resistance

Supplementary calcium restores peanut (Arachis hypogaea) growth and photosynthetic capacity under low nocturnal temperature

Peanut (Arachis hypogaea L.) is a globally important oil crop, which often experiences poor growth and seedling necrosis under low nocturnal temperatures (LNT). This study assessed the effects of supplementary calcium (Ca2+) and a calmodulin inhibitor on peanut growth and photosynthetic characteristics of plants exposed to LNT, followed by recovery at a higher temperature. We monitored key growth and photosynthetic parameters in a climate-controlled chamber in pots containing soil. LNT reduced peanut growth and dry matter accumulation, enhanced leaf nonstructural carbohydrates concentrations and non-photochemical quenching, decreased the electron transport rate, increased the transmembrane proton gradient, and decreased gas exchange rates. In peanuts subjected to LNT, foliar application of Ca2+ restored growth, dry matter production and leaf photosynthetic capacity. In particular, the foliar Ca2+ application restored temperature-dependent photosynthesis feedback inhibition due to improved growth/ sink demand. Foliar sprays of a calmodulin inhibitor further deteriorated the effects of LNT which validated the protective role of Ca2+ in facilitating LNT tolerance of peanuts

Inflorescence abscission protein SlIDL6 promotes low light intensityinduced tomato flower abscission

In many fruiting plant species, flower abscission is induced by low light stress. Here, we elucidated how signaling mediated by the peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) controls low light-induced flower drop in tomato (Solanum lycopersicum). We analyzed the expression patterns of an IDA-Like gene (SlIDL6) during low light-induced flower abscission, and used tandem mass spectrometry to identify and characterize the mature SlIDL6 peptide. Tomato knockout lines were created to investigate the in vivo function of SlIDL6. In addition, yeast one-hybrid assays were used to investigate the binding of the SlWRKY17 transcription factor to the SlIDL6 promoter, and silencing of SlWRKY17 expression delayed low light-induced flower abscission. SlIDL6 was specifically expressed in the abscission zone and at high levels during low light-induced abscission and ethylene treatment. SlIDL6 knockout lines showed delayed low light-induced flower drop, and the application of SlIDL6 peptide accelerated abscission. Overexpression of SlIDL6 rescued the ida mutant phenotype in Arabidopsis (Arabidopsis thaliana), suggesting functional conservation between species. SlIDL6-mediated abscission was via an ethylene-independent pathway. We report a SlWRKY17-SlIDL6 regulatory module that functions in low light promoted abscission by increasing the expression of enzymes involved in cell wall remodeling and disassembly