Iron is an essential element for most organisms. Both plants and microorganisms have developed different mechanisms for iron uptake, transport and storage. In the symbiosis systems, such as rhizobia–legume symbiosis and arbuscular mycorrhizal (AM) symbiosis, maintaining iron homeostasis to meet the requirements for the interaction between the host plants and the symbiotic microbes is a new challenge. This intriguing topic has drawn the attention of many botanists and microbiologists, and many discoveries have been achieved so far. In this review, we discuss the current progress on iron uptake and transport in the nodules and iron homeostasis in rhizobia–legume symbiosis. The discoveries with regard to iron uptake in AM fungi, iron uptake regulation in AM plants and interactions between iron and other nutrient elements during AM symbiosis are also summarized. At the end of this review, we propose prospects for future studies in this fascinating research area.

Ralstonia solanacearum, the causal agent of bacterial wilt, is recognized as one of the most destructive vascular pathogens. Plant defense responses are gradually developed through long-term interactions with R. solanacearum. The plant cell wall integrity (CWI) system has evolved to initiate defense responses via a diverse array of plasma membrane-resident sensors. These defense responses result primarily from physical and chemical actions that counteract infection with R. solanacearum. The plant cell wall serves as a defensive barrier against the pathogen, including cellulose, hemicellulose, pectin, lignin, and suberin. Various modifications to the cell wall and multiple changes in its composition are employed by plants resistant to R. solanacearum. Physical confinement vertically or horizontally induced in xylem tissues is the most effective method of defense against R. solanacearum. The timely formation of tyloses and gels within the vessel lumen contributes to the suppression of R. solanacearum. In addition, the deposition of callose at the infected sites reinforces the cell wall, thereby preventing the further spread of R. solanacearum. Morphological modifications, such as the thickening of the pit membranes and the increased number of larger xylem vessels, play crucial roles in conferring resistance to R. solanacearum. Secondary metabolites act as phytoalexins used by plants against R. solanacearum. In this review, we discuss the strategies deployed by plants resistant to R. solanacearum. In particular, we outline the physical and chemical restrictions, as well as the tissue constraints, against the vascular pathogen.

Descurainia sophia L. Webb ex Prantl is used in traditional medicine globally. However, the lack of an efficient and reliable genetic transformation system has seriously limited the investigation of gene function and further utilization of D. sophia. In this study, a highly efficient, time-saving, and cost-effective Agrobacterium tumefaciens-mediated genetic transformation system has been developed in D. sophia. In this method, the transformation was accomplished by simply dipping developing D. sophia inflorescences for 45 s into an Agrobacterium suspension (OD₆₀₀ = 0.6) containing 5% sucrose and 0.03% (v/v) Silwet L-77. Treated plants were allowed to set seeds which were then plated on a selective medium with hygromycin B (HygB) to screen transformants. Additionally, the CRISPR/Cas9 genomic editing system was validated by targeting phytoene desaturase (PDS) gene using this floral dip method, and mutant plants with the expected albino phenotype could be obtained in 2.5 months. This genetic transformation and targeted editing system will be a valuable tool for routine investigation of gene function and further exploitation in D. sophia.

Quercetin glucosides are important phytopharmaceutical metabolites in Descurainia sophia seeds, which are widely used in traditional herbal medicine. However, the key genes involved in quercetin glucoside biosynthesis in D. sophia have not been characterized. Herein, we present the telomere-to-telomere genomes of a tetraploid D. sophia, which accumulates high levels of quercetin glucoside, and a diploid D. sophia, which accumulates only trace amounts. Multiomics analyses and uridine diphosphate glucosyltransferase (UGT) enzyme assays revealed that the gene duplication and functional evolution of Dscd6AG01520, an UGT gene, led to high quercetin-3-O-β-d-glucoside and quercetin-3,7-O-β-d-diglucoside accumulation in tetraploid D. sophia seeds. Further UGT enzyme assays with the point mutations of Dscd6AG01520 showed that S213 was a critical amino acid for the enzymatic activity of Dscd6AG01520. In addition, we found that diploid D. sophia evolved from an ancestral crucifer karyotype through chromosome fusion and rearrangement. Collectively, our findings illuminate the mechanism of high quercetin glucoside accumulation in tetraploid D. sophia, clarify the origin of the diploid D. sophia genome, and provide valuable genomic resources for comparative genomics and research into polyploid evolution.

Quorum sensing (QS) serves as a regulatory system of virulence factors in the Ralstonia solanacearum species complex (RSSC). The two-component system PhcS–PhcQ recognizes QS signals, subsequently activating the transcriptional regulator PhcA and promoting the expression of QS-dependent virulence factors. In this study, we identified a sensor histidine kinase (Shk) in the R. solanacearum strain GMI1000 and uncovered its essential roles in PhcA-dependent virulence. To investigate the functions of Shk in QS-dependent virulence, we generated an shk-deletion mutant (Δshk) and demonstrated that the deletion of shk leads to a lowered production of cellulase, biofilm, and exopolysaccharide. Moreover, the complementation of native shk in Δshk cell restored the QS-dependent phenotypes. However, the swarming motility of Δshk cells was significantly increased compared to the wild-type GMI1000 strain. The Δshk mutant exhibited impaired colonization of R. solanacearum in the xylem vessels of tomato plants, resulting in attenuated pathogenicity of Δshk to tomato plants. Consistent with the results of the virulence assay, the deletion of the shk gene of R. solanacearum led to the downregulation of the phcA, epsB, and cbhA genes in planta, while the expression of fliC was upregulated in the Δshk mutant relative to the wild-type GMI1000 strain. Pull-down assays suggested that RSc0040 functions as a response regulator for the sensor Shk in vivo and in vitro. Collectively, Shk is implicated in the regulation of these QS-dependent virulent factors, thereby contributing to the virulence of R. solanacearum to tomato plants.