The problem of potentially toxic metal pollution is increasingly acute with the development of human society. In this study, we investigated the remediation of nickel (Ni) and cadmium (Cd) co-contamination through inoculating rice with three new-isolated Ni- and Cd-resistant plant growth-promoting rhizobacteria (PGPR) Y3, Y4, and Y5. These three strains possessed growth-promoting properties, including 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, the ability of indoleacetic acid (IAA) production, phosphate solubilization, siderophores production, and exopolysaccharide (EPS) development. According to 16S rDNA sequence homology, strains Y3, Y4, and Y5 were identified as Pseudomonas sp., Chryseobacterium sp., and Enterobacter sp., respectively. Based on the results of rice germination experiments conducted under combined toxicity, we set the contamination concentrations for Ni²⁺ at 20 μg mL^-1 and Cd²⁺ at 40 μg mL^-1. Then we conducted potting experiments at these concentration levels to study the effects of strains Y3, Y4, and Y5 on rice growth under synergistic Ni and Cd stress. The results indicated that the inoculated strains Y3, Y4, and Y5 were effective in promoting the growth of rice seedlings under the combined stress of Ni and Cd, and conferring tolerance to Ni and Cd by increasing the antioxidant enzyme activities of the seedlings. Among them, strain Y3 exhibited stronger ACC deaminase activity, IAA production capacity, and EPS production capacity, showing the most pronounced growth-promoting effect on rice. It was demonstrated that after inoculation with strain Y3, the germination rate of rice seeds increased by 43 %, the fresh weight of stems improved by 35 %, and the chlorophyll content enhanced by 70 % and other growth-promoting phenomena. Additionally, under Ni and Cd stress, strain Y5 performed better than strain Y4 in terms of IAA production capacity and its influence on rice root growth, suggesting that IAA production might play a specifically essential role in root growth under Ni and Cd stress.

Potato late blight is an important disease in potato production, which causes serious damage. Salicylic acid (SA) is a plant hormone involved in the regulation of potato ( Solanum tuberosum ) resistance to Phytophthora infestans . In this study, it was found that exogenous methyl salicylate (MeSA) treatment could significantly enhance the resistance of potato to P. infestans . RNA‐seq results confirmed that SA was important for potato resistance to P. infestans . Salicylic acid binding protein 2 (SABP2) is a member of α/β hydrolase family, which can convert MeSA into SA to regulate the steady state of SA in plants. StSABP2 protein was obtained through prokaryotic expression, and enzymatic analysis in vitro confirmed that StSABP2 could transform MeSA into SA. In order to explore the function of StSABP2 in the process of plant resistance to P. infestans , we carried out virus‐mediated gene silencing of StSABP2 in potato and transiently expressed StSABP2 in tobacco. The results showed that StSABP2 positively regulated plant resistance to P. infestans , and this process was achieved by mediating the transcription of SA signal and defence‐related genes. Then we screened for the upstream regulator of StSABP2 . The results of double luciferase and yeast one‐hybrid analysis showed that StNAC2 could activate the transcription of StSABP2 . The StNAC2‐StSABP2 module regulated potato resistance to P. infestans by positively mediating the SA pathway. This study provides a new idea for improving host resistance to potato late blight by regulating the SA signal in potato and provides germplasm resources for potato resistance breeding.

Previous studies have demonstrated that Bacillus velezensis HN-Q-8 shows significant inhibitory effects against various plant pathogenic fungi causing potato diseases, primarily attributed to the production of fengycin. However, the low yield of fengycin in wild-type strains limits its practical application, and the influence of its biosynthesis pathway on volatile organic compound production remains unclear. In this study, to enhance fengycin production in Bacillus velezensis HN-Q-8, we applied metabolic engineering by targeting competitive pathways. Specifically, a double mutant (ΔsrfAAΔbaeBE) was constructed by knocking out the surfactin synthase gene srfAA and the bacillaene synthesis gene baeBE. The fengycin yield of the ΔsrfAAΔbaeBE mutant in the basal (sodium glutamate) fermentation medium reached 98.83 mg/L, representing a 2.39-fold increase over the wild-type strain. Subsequent medium optimization by supplementing peptone further boosted production to 155.61 mg/L, which was 3.77-fold higher than the wild-type level. The lipopeptide extract from the double mutant strain ΔsrfAAΔbaeBE demonstrated potentiated antifungal activity against four major potato fungal pathogens: Alternaria solani (early blight), Rhizoctonia solani (black scurf), Fusarium oxysporum (wilt), and Botrytis cinerea (gray mold). The active volatile compounds released by ΔsrfAAΔbaeBE, such as benzaldehyde and 2,5-dimethylpyrazine were significantly increased. The knockout of srfAA and baeBE also distinctly altered the physiology of the strain: the double mutant exhibited enhanced biofilm formation, an accelerated early growth rate followed by early decline, and a severely reduced sporulation capacity. These results confirmed the feasibility of molecularly modifying Bacillus velezensis HN-Q-8 to improve fengycin production and antifungal activity for further agricultural application.

Potato early blight is a fungal disease caused by Alternaria solani that seriously affects potato production. Catalase (CAT), an important antioxidant enzyme in plants, regulates the basal immune response to necrotrophic pathogens by decomposing hydrogen peroxide (H₂O₂); however, its role in potato early blight remains unclear. The results revealed that using a H₂O₂ biosensor for transient overexpression in Nicotiana benthamiana, we found that A. solani infection significantly induced sustained H₂O₂ accumulation in tobacco leaves. Exogenous application of H₂O₂ to potato leaves followed by inoculation with A. solani showed that elevated H₂O₂ levels promoted infection by the pathogen. StCAT1 expression was upregulated upon A. solani infection. Silencing StCAT1 in potato reduced antioxidant enzyme activities (SOD, PAL, CAT) and disease resistance, accompanied by elevated H₂O₂ accumulation. Overexpression of StCAT1 enhanced antioxidant enzyme activities and disease resistance while decreasing H₂O₂ levels. Additionally, StABI5 was identified as an upstream transcription factor that activates StCAT1 expression, and silencing StABI5 compromised potato resistance to early blight. In conclusion, this study confirms that StCAT1 acts as a positive regulatory factor and mediates potato resistance to early blight through the StABI5-StCAT1 signaling pathway, providing scientific basis and genetic resources for disease-resistant breeding.