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Summary Brassica rapa displays a wide range of morphological diversity which is exploited for a variety of food crops. Here we present a high‐quality genome assembly for pak choi (Brassica rapa L. subsp. chinensis), an important non‐heading leafy vegetable, and comparison with the genomes of heading type Chinese cabbage and the oilseed form, yellow sarson. Gene presence–absence variation (PAV) and genomic structural variations (SV) were identified, together with single nucleotide polymorphisms (SNPs). The structure and expression of genes for leaf morphology and flowering were compared between the three morphotypes revealing candidate genes for these traits in B. rapa. The pak choi genome assembly and its comparison with other B. rapa genome assemblies provides a valuable resource for the genetic improvement of this important vegetable crop and as a model to understand the diversity of morphological variation across Brassica species.

IntroductionSoil pollution caused by toxic elements such as lead (Pb) and cadmium (Cd) induces environmental stress on vegetable plants and soil microbial communities, reducing crop yield and disrupting ecosystem functions.MethodologyIn this study, nanoscale zerovalent iron supported with eggshell biochar and activated carbon (nZVI-ESB/AC) was synthesized using carbothermal reduction synthesis and evaluated the effectiveness in minimizing the toxicity of lead and cadmium in soil and alleviating the toxic effects of these metals on Brassica chinensis L. and soil microbial communities.ResultsThe nZVI-ESB/AC immobilized Pb and Cd in the soil more than ordinary eggshell biochar, resulting in their lower bioaccumulation in the edible part of Brassica chinensis L. The nZVI-ESB/AC treatments were significantly more effective than biochar treatments in enhancing plant growth, reducing oxidative stress indicators by 1.5–2 folds, and increasing the relative abundance level of Bacilli and Clostridia by 52–67% and 10–15%, respectively. The presence of iron in nZVI-ESB/AC enhanced the activities of antioxidant enzymes, leading to the decreased generation of reactive oxygen species and lipid peroxidation in the plants.ConclusionsThis study demonstrates the potential of nZVI-ESB/AC as an effective adsorbent for soil remediation, alleviating stress induced by toxic metals on vegetable plants and promoting bacterial community diversity. The successful application of nZVI-ESB/AC presents promising prospects for sustainable agriculture, mitigating the environmental impact of lead and cadmium pollution and improving crop yield.

Plasmodiophora brassicae Woronin causes a devastating infectious disease known as clubroot that is damaging to cruciferous vegetables. This study aimed to isolate beneficial bacteria from the rhizosphere soil of pak choi (Brassica campestris sp. chinensis) and to evaluate the ability of the isolate to reduce the severity of clubroot. Strains obtained from the rhizosphere of symptomless pak choi were first selected on the basis of their germination inhibition rate and effects on the viability of P. brassicae resting spores. Eight bacterial isolates had inhibitory effects against the resting spores of clubroot causing pathogen. However, MZ-12 showed the highest inhibitory effect at 73.4%. Inoculation with MZ-12 enhanced the plant biomass relative to plants grown without MZ-12 as well as P. brassicae infected plants. Furthermore, enhanced antioxidant enzymatic activities were observed in clubroot-infected plants during bacterial association. Co-inoculation of the plant with both P. brassicae and MZ-12 resulted in a 64% reduction of gall formation in comparison to plants inoculated with P. brassicae only. Three applications of MZ-12 to plants infected with P. brassicae at 7, 14 and 21 days after seeding (DAS) were more effective than one application and repressed root hair infection. According to 16S rDNA sequence analysis, strain MZ-12 was identified as had a 100% sequence similarity with type strain Bacillus cereus. The findings of the present study will facilitate further investigation into biological mechanisms of cruciferous clubroot control.

Main conclusionBraANS.A3 was the key gene controlling purple leaf color in pak choi, and two short fragments of promoter region in green pak choi might be interfering its normal expression.Pak choi (B. rapa L. ssp. chinensis) is an influential and important vegetable with green, yellow, or purple leaves that is cultivated worldwide. The purple leaves are rich in anthocyanins, but the underlying genetics and evolution have yet to be extensively studied. Free-hand sections of the purple leaves indicated that anthocyanins mainly accumulate throughout the adaxial and abaxial epidermal leaf cells. Segregation analyses of an F2 population of a B. rapa ssp. chinensis L. purple leaf mutant ZBC indicated that the purple trait is controlled by an incompletely dominant nuclear gene. Bulked segregant analysis (BSA) showed that the key genes controlling the trait were between 24.25 and 38.10 Mb on chromosome A03 of B. rapa. From the annotated genes, only BraA03g050560.3C, homologous to Arabidopsis AtANS, was related to the anthocyanin synthesis pathway. Genome annotation results and transcriptional sequencing analyses revealed that the BraANS.A3 gene was involved in the purple leaf trait. qRT-PCR analyses showed that BraANS.A3 was highly upregulated in ZBC but hardly expressed in the leaves of an inbred homozygous line of B. campestris ssp. chinensis L. green leaf mutant WTC, indicating that BraANS.A3 played a key role catalyzing anthocyanin synthesis in ZBC. Full-length sequence alignment of BraANS.A3 in WTC and ZBC showed that it was highly conserved in the gene region, with significant variation in the promoter region. In particular, the insertion of two short fragments of the promoter region in WTC may interfere with its normal expression. The promoter regions of ANS in six Brassica species all had multiple cis-elements involved in responses to abscisic acid, light, and stress, suggesting that ANS may be involved in multiple metabolic pathways or biological processes. Protein–protein interactions predicted that BraANS.A3 interacts with virtually all catalytic proteins in the anthocyanin synthesis pathway and has a strong relationship with Transparent Testa 8 (TT8). These results suggest that BraANS.A3 promotes anthocyanin accumulation in purple pak choi and provide new insights into the functional analysis of anthocyanin-related genes in Chinese cabbage and transcriptional regulatory networks.

Background Studying how economic vegetable adapt to stressful environment is important not only for plant biology application but also to agronomy. In this study, we selected two commonly used genotypes of pak choi, i.e., larger green pak choi ( Brassica rapa ssp. chinensis ) and smaller purple pak choi ( Brassica rapa var. chinensis , ‘Rubi F1’) to examine the divergent response of the two genotypes to drought and shading in the semi-arid region of Xinjiang. We compared the differences in biomass accumulation and plant morphological traits of the two pak choi in response to the interaction effects of drought (55-70% of field water capacity) and shading (24% reduction of canopy light radiation). Results The results showed drought and shading significantly reduced the aboveground and belowground biomass of the two pak choi, with a particularly pronounced decrease in shoot biomass under the combined effect of shading + drought. The decline in shoot biomass was mostly resulted from decreasing in the number of leaves rather than in plant height and crown width in response to drought and shading. In terms of morphological traits, green pak choi sensitively responded to increased drought and shading, with aboveground biomass mostly determined by leaf number and root mass. In contrast, purple pak choi likely more resistant to the stressful environment, as its aboveground biomass was also influenced by plant height and crown width. Conclusions Hence it is important to consider not only the effects of drought but also the role of adequate light, which plays a key part in promoting the cultivation and growth of pak choi in stressful environments. The research and application of plant biology and agronomy in the region also need to consider the diversity of key economic plants to promote sustainability of vegetable farming in adapting to changing environmental stresses.

Polyploid plants generally demonstrate enhanced photosynthetic capacity compared to their diploid ancestors; however, the mechanisms underlying this phenomenon remain largely unexplored. This study utilizes pak choi [ Brassica campestris (syn. Brassica rapa ) ssp. chinensis ] as the material to investigate the molecular mechanisms underlying enhanced photosynthesis in autotetraploid. Our findings indicate that autotetraploid pak choi leaves exhibit increased thickness, enlarged intercellular spaces, and cell dimensions, as well as augmented accumulation of thylakoids and grana. Photosynthesis data indicate that the net photosynthesis ( Pn ) of autotetraploid plants is significantly greater than that of diploid plants. Transcriptome and miRNA sequencing revealed that the differentially expressed genes were significantly enriched in the photosynthesis thylakoid pathway. Joint analysis revealed that novel-miRNA117 regulates BcLhcb1 and BcLhcb4.2 , whereas Bc-miR403-5p regulates BcLhcb4.2 . The downregulation of BcLhcb1 , BcLhcb2.1 , and BcLhcb4.2 resulted in reduced Pn in pak choi, whereas their overexpression increased the growth of Arabidopsis and increased plant weight, which was attributed to the tight stacking of thylakoid granules in the overexpressing plants. Additionally, we observed weakened growth in Arabidopsis overexpressing novel-miRNA117 and Bc-miR403-5p, which was consistent with the phenotype resulting from the silencing of BcLhcbs . These findings further demonstrated that miRNA117 regulates BcLhcb1 and BcLhcb4.2 , whereas Bc-miR403-5p regulates BcLhcb2.1 . This study enhances our understanding of the molecular mechanisms underlying photosynthesis in homogenous autotetraploid pak choi. Furthermore, it provides novel insights into the regulatory roles of miRNAs in polyploid photosynthesis and contributes to the molecular breeding of pak choi.

The extensive mining of bastnasite (CeFCO 3 ) has caused severe pollution of lanthanum (La), cerium (Ce), and fluorine (F) in the surrounding farmland soil, threatening the safety of the soil-plant system. However, the stress effects of the interaction among these three elements on the tolerance and accumulation traits of Brassica chinensis L. ( B. chinensis ) are unclear. In this study, the interaction mechanisms of these three pollutants regulating the growth characteristics, antioxidant capacity, and accumulation characteristics of B. chinensis was explored using pot experiments of La-Ce (LC), Ce-F (CF), La-F (LF), and La-Ce-F (LCF) interactions. The LC interaction pollution treatments at the element concentrations higher than those of LC3 showed significant impact ( P  < 0.05) on the plant growth. The order of tolerance in B. chinensis under four interaction treatments was La-F > Ce-F > La-Ce-F > La-Ce, which was supported by the integrated biomarker response (IBR) analysis. The synergistic effect of La and Ce in La-Ce experiment promoted these two elements in the plants, whereas the presence of F in CF, LF, and LCF combined pollution treatments inhibited the absorption of La and Ce. Moreover, under the interaction among three elements, the synergistic effect of La and Ce in LC treatment enhanced the biotranslocation factor (BTF) of both elements, reaching the highest levels of 0.36 and 0.40, respectively. The addition of F in CF (BTF of 0.3 and 0.15, respectively), LF (BTF of 0.25 and 0.15, respectively), and LCF (BTF of 0.21, 0.24, and 0.15, respectively) treatments reduced the BTF of La and Ce in the plants due to the formation of insoluble precipitates between F with La or Ce. In conclusion, the interaction between La and Ce could reduce the tolerance of B. chinensis , while the presence of F could enhance the plant resistance to both La and Ce.

Heavy metal pollution in agricultural soils has become a widespread serious problem with the rapid industrialization and urbanization in the past two decades. Cadmium (Cd 2+ ) is of the most concern in soils due to its high toxicity. It is necessary to develop remediation strategies to remove or neutralize its toxic effects in Cd-contaminated soil. Microbial bioremediation is a promising technology to treat heavy metal-contaminated soils. In this study, Cd-resistant bacterium, isolated from heavy metal-polluted soil in Southern China, was characterized as Raoultella sp. strain X13 on the basis of its biochemical profile and 16S rRNA. We investigated the characterization of Cd 2+ distribution in different cellular compartments after Cd 2+ uptake. Cd 2+ uptake by strain X13 was mainly by ion exchange and chelation binding tightly to the cell wall. In addition, X13 plant growth-promoting characteristics suggested that X13 could solubilize phosphate and produce indole acetic acid. Pot experiments for the remediation of Cd-contaminated soil in situ by X13 inoculation demonstrated that X13 application to Cd-contaminated soils significantly promoted pak choi growth and improved production. We also found that X13 substantially reduced the Cd 2+ bioavailability for pak choi. Therefore, strain X13 is an effective treatment for potential application in Cd 2+ remediation as well as for sustainable agronomic production programs in Cd-contaminated soils.

With the large-scale use of plastic products in daily life and the progress of industrial production, it has had a serious impact on the soil environment. To identify the effect of heavy metal and microplastics on the development of plants, we examined the changes of physiological and biochemical indexes of Brassica chinensis var. chinensis under different concentrations of heavy metal cadmium and polyethylene stress with a pot experiment. We set three cadmium concentration gradients—0, 10, 20 mg/kg and three polyethylene concentration gradients—0, 18, 36 g/kg in the experiment. The results showed that both cadmium concentration and polyethylene concentration have significant effects on chlorophyll content, enzyme activity, and root development (except for the effect of polyethylene concentration on root volume, superoxide anion free radical content, and peroxidase activity), and the addition of polyethylene alleviated the stress effect of cadmium on biomass, root system, and chlorophyll content. The stress of cadmium and polyethylene reduced the leaf and root biomass of B. chinensis var. chinensis and inhibited the activities of enzymes related to chlorophyll synthesis, while the content of superoxide anion free radicals in the leaves increased, causing the enhancement of catalase activity. In addition, the content of photosynthetic pigments decreased, suggesting that the capture of light energy by B. chinensis var. chinensis will be reduced. These findings provide a new insight into the toxic effects of microplastics and heavy metals on B. chinensis var. chinensis, and further apply to the ecological risk assessment of microplastics and heavy metals on higher plants.

Triadimefon is a typical systemic fungicide that is widely used in the management of powdery mildew, rust disease, and southern blight. In this study, we measured fungicide residue to profile its absorption, translocation, and accumulation in three representative vegetable crops (Pak choi, cucumber, and pepper) after over-application. The fungicides were applied through entire-plant spraying (EPS), root-irrigation (RI), and middle-leaf-daubing (MLD). The half-life of triadimefon depends on the application method and plant species. In EPS, the half-life was 5.42 days (Pak choi), 6.86 days (cucumber), and 6.73 days (pepper), while in RI it was 4.39 days (Pak choi), 6.30 days (cucumber), and 5.98 days (pepper). In the EPS treatment, triadimefon is translocated both upward/outside and downward/inner-side from the daubed leaves in all the three vegetable crops. The transfer amount to each organ reached a peak on the 2nd day after fungicide application. The mesophyll of Pak choi exhibited a higher fungicide deposition compared to the petiole. In cucumber and pepper, the leaves demonstrated the highest accumulation of triadimefon (approximately 0.3–0.5 mg·kg −1 ), followed by stems. Roots and fruits displayed the lowest levels of triadimefon accumulation. Furthermore, triadimefon was found to have an impact on chlorophyll content, root activity, as well as the activity of superoxide dismutase and catalase in Pak choi, indicating its potential as a plant growth regulator. These aforementioned studies provide novel insights for the safe and efficient application of triadimefon in the production of Pak choi, cucumber, and pepper.