Abstract In the cyanobacterium Synechocystis sp. PCC 6803, the capacity for the repair of photosystem II (PSII) is closely associated with the tolerance of PSII to strong light. However, it remains unclear whether the capacity for PSII repair also contributes to the tolerance of PSII to high-temperature stress. In this study, we examined the tolerance of PSII to high temperatures in transformants of Synechocystis that had been engineered to enhance the capacity for PSII repair, specifically via the overexpression of reactive oxygen species- (ROS-) scavenging enzymes (superoxide dismutase and catalase) and exploiting a mutated derivative of EF-Tu, a translation factor that is sensitive to oxidation by ROS. When cells were exposed to the high temperature of 46 °C under standard growth illumination, the activity of PSII in transformants declined more slowly than that in wild-type cells. This mitigation of the heat-induced inactivation of PSII was attributed to enhancements of both the capacity for PSII repair and the thermostability of the PSII complex itself. The synthesis de novo of the D1 protein at 46 °C in the transformants was maintained at higher levels than that in wild-type cells. The heat-induced accumulation of intracellular ROS was significantly suppressed in the transformants. Furthermore, net photosynthetic activity and cell viability at high temperatures were enhanced in the transformants. Thus, reinforcement of both antioxidant defenses and translational systems might improve not only the repair of PSII but also the thermostability of PSII, leading to the enhanced thermotolerance of net photosynthesis and overall cell viability at elevated temperatures.
Tartary buckwheat (Fagopyrum tataricum) is renowned for its adaptability to complex growing conditions and stress tolerance. However, soil-borne necrotrophic pathogens such as Rhizoctonia solani frequently cause devastating diseases that severely compromise its yield and quality. In this study, through a genome-wide association study (GWAS), we identified a carboxylesterase gene, FtCES18, and demonstrated that it acts as a core positive regulator of disease resistance in Tartary buckwheat. Overexpression of FtCES18 significantly enhanced plant resistance, whereas virus-induced gene silencing (VIGS) led to a highly susceptible phenotype. Further analyses revealed that FtCES18 efficiently catalyzes the hydrolysis of methyl jasmonate (MeJA) into free jasmonic acid (JA), which initiates downstream JA-Ile signaling and rapidly promotes endogenous jasmonate accumulation upon pathogen infection. This JA signaling cascade reprograms host flavonoid metabolism, promoting the substantial accumulation of downstream defensive flavonoids (such as rutin and quercetin). Furthermore, we found that the transcription factor FtMYB32 directly binds to the MBS cis-element in the FtCES18 promoter to activate its expression. Notably, evolutionary analysis revealed a domestication-associated C-terminal truncation in the cultivated FtMYB32 that impairs its transactivation capacity, explaining the compromised basal resistance in cultivated accessions compared to their wild ancestors. Crucially, a natural single-nucleotide polymorphism (SNP) in the FtMYB32 promoter defines a superior haplotype (hapC) conferring enhanced basal transcriptional activity. This natural variation in promoter activity controls the expression abundance of the FtMYB32-FtCES18 module via a "dosage fine-tuning" effect, which is subsequently amplified by the downstream metabolic cascade, ultimately contributing to the natural variation in disease resistance among different Tartary buckwheat accessions. This study provides valuable genetic resources and a theoretical basis for breeding novel Tartary buckwheat varieties with high disease resistance.
Concerted evolution is the model by which multicopy gene families are homogenized across genomes, with ribosomal DNA (rDNA) as its textbook example. However, the extent and efficiency of this process may vary depending on genomic factors. The plant family Asteraceae provides a natural comparative system to address the evolutionary dynamics of rDNA, as it is uniquely characterized by the coexistence of two contrasting genomic arrangements: a separate (S-type) and a linked (L-type) organization of 5S and 35S rRNA genes. Here we analyzed rDNA arrangements in 71 representative Asteraceae species (50 S-type and 21 L-type) and, using WGS data and repeatome analyses, we have reconstructed full rDNA units and quantified the intragenomic variability across coding (genic) and non-coding (spacer) regions. No intermediate (coexisting L-type+S-type) genotypes were found. Our results reveal contrasting patterns of 5S rDNA variation depending on its genomic context. S-type species exhibit high levels of 5S polymorphism in both genic and spacer regions, while L-type species show near-complete sequence homogeneity, consistent with variation in homogenization efficiency and selective constraints related to copy number and chromosomal position of 5S rRNA genes. In contrast, 35S rDNA shows a low polymorphism level overall. The findings support a context-dependent view of concerted evolution across rDNA and highlight the influence of genome architecture on rDNA evolution. In particular, the contrasting behavior of 5S (highly conserved when linked but highly variable when separate) emerges as a key example of how structural genomic context shapes the evolution of even the most conserved housekeeping genes.
Apple is a globally significant fruit tree with considerable economic value. However, it is severely affected by soil salinization, which leads to a reduction in both yield and quality. Since salt tolerance in grafted apple trees largely depends on the rootstock, this study compared transcriptomic responses between salt-tolerant (R5-5) and salt-sensitive (M9T337) rootstocks under salt stress. A key salt-responsive gene, MdWRKY33d, was identified. Overexpressing MdWRKY33d in apple improved salt tolerance, while silencing it had the opposite effect. Additionally, under salt stress, compared with the control, chlorophyll fluorescence values, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) levels were elevated in MdWRKY33d transgenic apple and poplar materials. Functional analyses demonstrated that MdWRKY33d directly activates the expression of Peroxidase55 (MdPER55) and Dehydration-Responsive Element-Binding protein1D (MdDREB1D), thereby enhancing reactive oxygen species (ROS) scavenging and salt tolerance in transgenic plants. Yeast two-hybrid screening identified MdVQ22 as an interacting partner of MdWRKY33d, which was confirmed by pull-down, bimolecular fluorescence complementation (BiFC), and luciferase complementation imaging (LCI) assays. MdVQ22 negatively regulated apple salt tolerance by suppressing MdWRKY33d-mediated transcriptional activation of MdPER55 and MdDREB1D. Collectively, this study explores a putative regulatory module MdVQ22-MdWRKY33d-MdPER55/MdDREB1D to coordinate the responses to apple salt stress and provides potential targets for engineering salt-tolerant varieties.
Soybean (Glycine max (L.) Merr.) produces triterpenoid saponins, called soyasaponins, which are categorised as 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) saponins and group A saponins based on the chemical modifications at the C-22 position of their triterpene skeleton. These C-22 modifications confer different biological functions. While most genes involved in soyasaponin biosynthesis have been identified, the enzymes responsible for conjugation of DDMP or arabinose to the C-22 hydroxyl group remain unclear. This study aimed to identify the enzymes involved in these modifications. Co-expression analysis using known saponin biosynthetic genes identified three candidate UGT genes. Among them, UGT73K5 was essential for DDMP saponin biosynthesis in soybean, as ugt73k5 mutants lacked these compounds. Similarly, the orthologous gene in Lotus japonicus, UGT73K6, was required for DDMP saponin biosynthesis, and the ugt73k6 defect was complemented by soybean UGT73K5. In addition, UGT73BU1, a homologous gene not co-expressed with known saponin biosynthetic genes, was identified as a C-22 arabinosyltransferase involved in group A saponin biosynthesis. In L. japonicus, UGT73K6 is genomically co-localised and co-expressed with a cytochrome P450 gene responsible for C-22 hydroxylation, forming a conserved biosynthetic gene cluster. This organisation suggests coordinated biosynthetic modules underlying DDMP saponin production in legumes.
