The MADS-box protein is an important transcription factor in plants and plays an important role in regulating the plant abiotic stress response. In this study, a total of 94 MADS-box genes were predicted in the litchi genome, and these genes were widely distributed on all the chromosomes. The LcMADS-box gene family was divided into six subgroups (Mα, Mβ, Mγ, Mδ, MIKC, and UN) based on their phylogenetical relationships with Arabidopsis, and the closely linked subgroups exhibited more similarity in terms of motif distribution and intron/exon numbers. Transcriptome analysis indicated that LcMADS-box gene expression varied in different tissues, which can be divided into universal expression and specific expression. Furthermore, we further validated that LcMADS-box genes can exhibit different responses to various stresses using quantitative real-time PCR (qRT-PCR). Moreover, physicochemical properties, subcellular localization, collinearity, and cis-acting elements were also analyzed. The findings of this study provide valuable insights into the MADS-box gene family in litchi, specifically in relation to stress response. The identification of hormone-related and stress-responsive cis-acting elements in the MADS-box gene promoters suggests their involvement in stress signaling pathways. This study contributes to the understanding of stress tolerance mechanisms in litchi and highlights potential regulatory mechanisms underlying stress responses.

Class III peroxidases (CIII PRXs) are plant-specific enzymes with high activity that play key roles in the catalysis of oxidation-reduction reactions. In plants, CIII PRXs can reduce hydrogen peroxide to catalyze oxidation–reduction reactions, thereby affecting plant growth, development, and stress responses. To date, no systematic analysis of the CIII PRX gene family in litchi (Litchi chinensis Sonn.) has been documented, although the genome has been reported. In this study, a total of 77 CIII PRX (designated LcPRX) gene family members were predicted in the litchi genome to provide a reference for candidate genes in the responses to abiotic stresses during litchi growth and development. All of these LcPRX genes had different numbers of highly conserved PRX domains and were unevenly distributed across fifteen chromosomes. They were further clustered into eight clades using a phylogenetic tree, and almost every clade had its own unique gene structure and motif distribution. Collinearity analysis confirmed that there were eleven pairs of duplicate genes among the LcPRX members, and segmental duplication (SD) was the main driving force behind the LcPRX gene expansion. Tissue-specific expression profiles indicated that the expression levels of all the LcPRX family members in different tissues of the litchi tree were significantly divergent. After different abiotic stress treatments, quantitative real-time PCR (qRT-PCR) analysis revealed that the LcPRX genes responded to various stresses and displayed differential expression patterns. Physicochemical properties, transmembrane domains, subcellular localization, secondary structures, and cis-acting elements were also analyzed. These findings provide insights into the characteristics of the LcPRX gene family and give valuable information for further elucidating its molecular function and then enhancing abiotic stress tolerance in litchi through molecular breeding.

As an important regulatory protein phosphatase in the abscisic acid (ABA) signal transduction pathway and mitogen-activated protein kinases (MAPK) cascade, type-2C protein phosphatase (PP2C) plays crucial roles in plant responses to abiotic stresses. However, the PP2C gene family’s responses to abiotic stress in litchi (Litchi chinensis Sonn.) have not been systematically studied. In this study, we predicted the 68 PP2C (designated LcPP2C) genes randomly distributed across fourteen chromosomes in the litchi genome. Phylogenetic tree analysis among litchi, Arabidopsis (Arabidopsis thaliana), and rice (Oryza sativa) revealed that the phylogenetic tree was divided into thirteen groups (A, B, C, D, E, F1, F2, G, H, I, J, K, and L). Closely linked LcPP2C genes within the same group exhibited various similarities in gene structures and motif compositions. Collinearity analysis demonstrated that segmental duplication (SD) events were the main dramatically increasing numbers in the LcPP2C gene family members. Cis-acting element analysis revealed that the 68 LcPP2C genes contained hormone and stress response elements with varying quantities, implying their potential in litchi stress resistance. Expression analysis showed that all the LcPP2C genes exhibited varying expression levels across nine different litchi tissues, more than 50% of genes within each group displayed similar tissue-specific expression patterns. The expression intensity, duration and regulation direction (up- or down-regulation) of the LcPP2C genes were varied under different abiotic stresses (cold, heat, and drought). The physiological and biochemical tests indicated that eight activation indexes (peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA), proline (PRO), soluble protein (SP), hydrogen peroxide (H₂O₂), and soluble sugar (SS)) increase at different level. Additionally, we analyzed physicochemical properties, subcellular locations, and secondary structures of the LcPP2C family members. Notably, the extensive connectivity of LcPP2C32/60/9/37 underscored their vital roles in orchestrating and regulating biomolecular networks. These results provide valuable information for the identification of the LcPP2C genes and ideas for the cultivation of its transgenic induction lines in litchi.

Superoxide dismutase (SOD) serves as a critical enzyme that is involved in plant development and abiotic stresses by effectively detoxifying reactive oxygen species (ROS). Though the SOD gene family has been reported across various plant species, its specific members and functional roles in litchi (Litchi chinensis Sonn.) remain poorly understood. In this study, a total of seven SOD (christened LcSOD) genes were identified from the litchi genome and classified into three groups across six chromosomes. Notably, genes from the same evolutionary branch had more similar structures and motif distributions. The LcSOD genes were confirmed to have a stronger collinearity with dicotyledons than with monocotyledons. Cis-acting elements analysis indicated that the LcSOD gene family was deeply involved in orchestrating growth, development, and responses to multiple phytohormones and diverse stresses. Expression patterns of the LcSOD genes across different tissues revealed universal and specific expressions. In leaves, expression levels of the LcSOD genes were induced by cold, heat, drought, and salt stresses, and transcript levels correlated positively with concomitant changes in key physiological parameters under the same conditions. In addition, the LcSOD genes were characterized for their physicochemical properties, subcellular localizations, secondary and tertiary structures, gene ontology (GO) annotations, and protein-protein interactions. Our findings offer comprehensive insights into the LcSOD gene family, enriching genetic resources. They provide a framework for functional characterization and the development of stress-resistant cultivars, driving both basic research and applied breeding programs in litchi.

Biochar, a highly effective amendment, is widely used for soil improvement and environmental remediation. However, research on its application in litchi (Litchi chinensis) cultivation is relatively scarce, particularly regarding its potential to enhance the rhizospheric soil ecological environment. In this study, a pot experiment was conducted to investigate the effects of biochar derived from maize (Zea mays) and rice (Oryza sativa), applied at different rates (3%, 6%, 10%), on the physical and chemical properties, enzyme activities, and microbial community structure and diversity in the rhizospheric soil of litchi seedlings. The results showed that biochar application significantly (p < 0.05) improved soil nutrient conditions, including total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), available potassium (AK), pH, and soil sucrase (SC) enzyme activity. Notably, treatment with 10% maize biochar exhibited the most pronounced improvement across all parameters, barring AP. Furthermore, biochar application stimulated the proliferation of specific bacterial taxa (Acidobacteriota, Bacteroidota, and Chloroflexota) and fungal phyla (Ascomycota and Mortierellomycota), increasing bacterial diversity while decreasing fungal diversity and richness. Correlation analysis further revealed the close relationships between soil microbial communities and fertility factors. This study provides substantial evidence regarding the efficacy and feasibility of biochar in improving the rhizospheric soil ecological environment of litchi. It offers a theoretical foundation for the scientific application of biochar in orchard soil management.