As a secondary messenger, calcium participates in various physiological and biochemical reactions in plants. Photosynthesis is the most extensive biosynthesis process on Earth. To date, researchers have found that some chloroplast proteins have Ca²⁺-binding sites, and the structure and function of some of these proteins have been discussed in detail. Although the roles of Ca²⁺ signal transduction related to photosynthesis have been discussed, the relationship between calcium and photosynthesis is seldom systematically summarized. In this review, we provide an overview of current knowledge of calcium’s role in photosynthesis.

Soil salinization is an important factor limiting food security and ecological stability. As a commonly used greening tree species, Robinia pseudoacacia often suffers from salt stress that can manifest as leaf yellowing, decreased photosynthesis, disintegrated chloroplasts, growth stagnation, and even death. To elucidate how salt stress decreases photosynthesis and damages photosynthetic structures, we treated R. pseudoacacia seedlings with different concentrations of NaCl (0, 50, 100, 150, and 200 mM) for 2 weeks and then measured their biomass, ion content, organic soluble substance content, reactive oxygen species (ROS) content, antioxidant enzyme activity, photosynthetic parameters, chloroplast ultrastructure, and chloroplast development-related gene expression. NaCl treatment significantly decreased biomass and photosynthetic parameters, but increased ion content, organic soluble substances, and ROS content. High NaCl concentrations (100–200 mM) also led to distorted chloroplasts, scattered and deformed grana lamellae, disintegrated thylakoid structures, irregularly swollen starch granules, and larger, more numerous lipid spheres. Compared to control (0 mM NaCl), the 50 mM NaCl treatment significantly increased antioxidant enzyme activity while upregulating the expression of the ion transport-related genes Na⁺/H⁺ exchanger 1(NHX 1) and salt overly sensitive 1 (SOS 1) and the chloroplast development-related genes psaA, psbA, psaB, psbD, psaC, psbC, ndhH, ndhE, rps7, and ropA. Additionally, high concentrations of NaCl (100–200 mM) decreased antioxidant enzyme activity and downregulated the expression of ion transport- and chloroplast development-related genes. These results showed that although R. pseudoacacia can tolerate low concentrations of NaCl, high concentrations (100–200 mM) can damage chloroplast structure and disturb metabolic processes by downregulating gene expression.

Legume crops are an important source of protein and oil for human health and in fixing atmospheric N₂ for soil enrichment. With an objective to accelerate much-needed genetic analyses and breeding applications, draft genome assemblies were generated in several legume crops; many of them are not high quality because they are mainly based on short reads. However, the superior quality of genome assembly is crucial for a detailed understanding of genomic architecture, genome evolution, and crop improvement. Present study was undertaken with an objective of developing improved chromosome-length genome assemblies in six different legumes followed by their systematic investigation to unravel different aspects of genome organization and legume evolution. We employed in situ Hi-C data to improve the existing draft genomes and performed different evolutionary and comparative analyses using improved genome assemblies. We have developed chromosome-length genome assemblies in chickpea, pigeonpea, soybean, subterranean clover, and two wild progenitor species of cultivated groundnut (A. duranensis and A. ipaensis). A comprehensive comparative analysis of these genome assemblies offered improved insights into various evolutionary events that shaped the present-day legume species. We highlighted the expansion of gene families contributing to unique traits such as nodulation in legumes, gravitropism in groundnut, and oil biosynthesis in oilseed legume crops such as groundnut and soybean. As examples, we have demonstrated the utility of improved genome assemblies for enhancing the resolution of “QTL-hotspot” identification for drought tolerance in chickpea and marker-trait associations for agronomic traits in pigeonpea through genome-wide association study. Genomic resources developed in this study are publicly available through an online repository, ‘Legumepedia’. This study reports chromosome-length genome assemblies of six legume species and demonstrates the utility of these assemblies in crop improvement. The genomic resources developed here will have significant role in accelerating genetic improvement applications of legume crops.

Intercropping systems have been studied as a sustainable agricultural planting pattern to increase soil quality and crop yields. However, the relationships between metabolites and soil physicochemical properties remain poorly understood under sugarcane/peanut intercropping system. Thus, we determined the rhizosphere soil physicochemical properties, and analyzed rhizosphere soil metabolites and root metabolites by metabolomics method under monoculture and intercropping patterns of sugarcane and peanut. The results showed that pH, the contents of total phosphorus (P), total potassium (K), available nitrogen (N), available phosphorus (P), and available potassium (K) were higher in rhizosphere soil of intercropping peanut than monoculture peanut, and the content of total P was higher in rhizosphere soil of intercropping sugarcane than monoculture sugarcane. Sugarcane/peanut intercropping also significantly increased the activities of acid phosphatase and urease in rhizosphere soil. The metabolomics results showed that 32 metabolites, mainly organic acids and their derivatives (25.00%), nucleotides and their metabolites (18.75%), were detected in root and rhizosphere soil samples. In the MP-S (rhizosphere soil of monoculture peanut) vs. IP-S (rhizosphere soil of intercropping peanut) comparison, 47 differential metabolites (42 upregulated) were screened, including glycerolipids (19.15%), organic acids and their derivatives (17.89%), and amino acids and their metabolites (12.77%). In the MS-S (rhizosphere soil of monoculture sugarcane) vs. IS-S (rhizosphere soil of intercropping sugarcane) comparison, 51 differential metabolites (26 upregulated) were screened, including heterocyclic compounds (15.69%), glycerolipids (11.76%), and organic acids and their derivatives (9.80%). The metabolite species from MP-S, MS-S, IP-S, and IS-S were similar, but some metabolite contents were significantly different, such as adenine, adenosine, maltotriose, thermozeaxanthin-13 and PE-NMe (20:0/24:0). Adenine and adenosine were detected in root and rhizosphere soils, and their levels were increased in the intercropping treatment, which were mainly related to enhanced purine metabolism in root and rhizosphere soils under the sugarcane/peanut intercropping system. Importantly, adenine and adenosine were significantly positively correlated with total P and total K contents, acid phosphatase and urease activities, and pH. This study clarified that the sugarcane/peanut intercropping system could improve soil nutrients and enzymes and was related to purine metabolism.

The NAC transcription factor (TF) is one of the most significant TFs in plants and is widely involved in plant growth, development, and responses to biotic and abiotic stresses. To date, there are no systematic studies on the NAC family in peanuts. Herein, 132 AhNACs were identified from the genome of cultivated peanut, and they were classified into eight subgroups (I–VIII) based on phylogenetic relationships with Arabidopsis NAC proteins and their conserved motifs. These genes were unevenly scattered on all 20 chromosomes, among which 116 pairs of fragment duplication events and 1 pair of tandem duplications existed. Transcriptome analysis showed that many AhNAC genes responded to drought and abscisic acid (ABA) stresses, especially most of the members in groups IV, VII, and VIII, which were expressed at larger differential levels under polyethylene glycol (PEG) and/or ABA treatment in roots or leaves. Furthermore, 20 of them selected in response to PEG and ABA treatment were evaluated by quantitative real-time polymerase chain reaction. The results showed that these genes significantly responded to drought and ABA in roots and/or leaves. This study was helpful for guiding the functional characterization and improvement of drought-resistant germplasms in peanuts.