Fenglan Zhang

Choy Sum (Brassica rapa subsp. chinensis var. parachinensis), also known as flowering Chinese cabbage, is an important stalk vegetable in Asia. However, the unique regulatory mechanism governing its “easy-bolting yet susceptible to premature bolting” trait remains poorly understood. The phosphatidyl ethanolamine-binding protein (PEBP) family serves as a central regulator of bolting, flowering, and growth development in plants. But this gene family has not been systematically identified and studied in Choy Sum yet. Therefore, this study systematically identified and analyzed the members of the PEBP gene family in Choy Sum using bioinformatics, transcriptomics, real-time fluorescence quantification, subcellular localization, and transgenic techniques. A total of 12 BcPEBP genes were identified and categorized into three subfamilies: FT-like, TFL1-like, and MFT-like. Phylogenomic analyses revealed family expansion through whole-genome duplication with strong purifying selection. Most members have highly conserved core motifs and gene structures. Protein sequence alignment showed that BcFT-2 and BcTFL-2 underwent non-synonymous mutations at key residues. The analysis of cis-acting elements suggests that the BcPEBP gene may be influenced by complex hormone and light regulatory networks. Expression profiling demonstrated leaf-specific upregulation of BcFT-1/2 during development and shoot apices-predominant expression of BcTFL1 genes, and the expression between homologous genes of BcTFL1-1/3 is more refined. Subcellular localization confirmed dual nuclear and plasma membrane targeting of BcFT-1/2 proteins. Overexpression of BcFT-1/2 in transgenic Arabidopsis promotes flowering. These findings establish BcPEBP genes as key bolting regulators and provide molecular targets for breeding-improved varieties.

Postharvest leaf senescence is a pivotal determinant influencing the quality and shelf life of leafy vegetables, exemplified by pak choi (Brassica rapa L. subsp. chinensis). While the regulatory role of gibberellin (GA) in modulating leaf senescence has been documented across diverse plant species, the underlying physiological and molecular mechanisms remain insufficiently characterized. This study, through a combination of transcriptomic and metabolomic analyses, investigated the effect of exogenous GA on postharvest leaf senescence in pak choi. GA treatment alleviated etiolation, maintained chlorophyll levels, reduced conductivity and malondialdehyde content, and delayed the onset of senescence symptoms in postharvest pak choi. Transcriptome profiling indicated that GA suppressed the expression of the senescence-associated genes BraSRGs and BraSAGs. In addition, GA influenced chlorophyll degradation and preserved chlorophyll content by modulating the expression of genes implicated in chlorophyll metabolism, including BraPPH, BraSGR1, BraNYCI, and BraPAO. GA treatment impacted lipid levels and regulated the degradation of membrane phospholipids. Furthermore, exogenous GA treatment disrupted the efficacy of the jasmonic acid signal pathway, primarily through the transcriptional downregulation of key regulatory genes, including BraJAZ10 and BraJAR1. These results provide insights into the role of GA in delaying postharvest leaf senescence and highlight potential targets for improving postharvest management in leafy vegetables.

Pathogens significantly restrict the production of Brassica rapa (B. rapa L. ssp. Pekinensis), with climate change and evolving planting patterns exacerbating disease prevalence. Multichannel rapid diagnostic methods in the field can facilitate the early detection and control of diseases in B. rapa. Here, we established a multichannel lateral flow biosensor (LFB) combined with a CRISPR/Cas12a cleavage assay for the simultaneous detection of four B. rapa diseases. Key innovations of this study include: (1) High specificity and sensitivity, down to pathogen concentrations of 1.5 pg/μl—due to the optimization of crRNA secondary structure: the more stable the crRNA, the higher its detection sensitivity. (2) Optimized visual detection parameters. We identified ideal concentration ratios for the visual fluorescence detection system: 50 nM Cas12a, 50 nM crRNA, and 500 nM ssDNA fluorescent probe. Furthermore, the optimal concentrations of components on the LFB detection system were 3 μl SA-GNPs, 500 nM ssDNA test strip probe, 0.5 mg/ml biotin-BSA as the test line, and 1 mg/ml anti-FITC as the control line. (3) Field-Ready Cas-AIRPA Platform. We developed the on-site Cas-AIRPA platform for the simultaneous detection of B. rapa pathogens by combining rapid nucleic acid extraction and a four-channel lateral flow biosensor (4-LFB), which quickly provides disease-related information through a specific 2D barcode. Analysis of B. rapa samples in the field confirmed the suitability of the Cas-AIRPA platform for rapid (~25 min) and simultaneous on-site detection of four diseases of B. rapa. This platform can also be adapted to detect other plant diseases in the field.

Global warming has a severe impact on the flowering time and yield of crops. Histone modifications have been well-documented for their roles in enabling plant plasticity in ambient temperature. However, the factor modulating histone modifications and their involvement in habitat adaptation have remained elusive. In this study, through genome-wide pattern analysis and quantitative-trait-locus (QTL) mapping, we reveal that BrJMJ18 is a candidate gene for a QTL regulating thermotolerance in thermotolerant B. rapa subsp. chinensis var. parachinensis (or Caixin, abbreviated to Par). BrJMJ18 encodes an H3K36me2/3 Jumonji demethylase that remodels H3K36 methylation across the genome. We demonstrate that the BrJMJ18 allele from Par (BrJMJ18^Par) influences flowering time and plant growth in a temperature-dependent manner via characterizing overexpression and CRISPR/Cas9 mutant plants. We further show that overexpression of BrJMJ18^Par can modulate the expression of BrFLC3, one of the five BrFLC orthologs. Furthermore, ChIP-seq and transcriptome data reveal that BrJMJ18^Par can regulate chlorophyll biosynthesis under high temperatures. We also demonstrate that three amino acid mutations may account for function differences in BrJMJ18 between subspecies. Based on these findings, we propose a working model in which an H3K36me2/3 demethylase, while not affecting agronomic traits under normal conditions, can enhance resilience under heat stress in Brassica rapa.

Key message BrLMI1 is a positive regulatory factor of leaf lobe formation in non-heading Chinese cabbage, and cis-regulatory variations lead to the phenoty

Summary: Leaf shape is a vital economic and developmental trait in leafy vegetable Chinese cabbage ( Brassica rapa L. subsp. pekinensis ), which varies from smooth to deeply lobed, whereas the molecular basis remains unclear. Here, we detected an incompletely dominant major quantitative trait locus (QTL) qBrrLLA10 for the lobed-leaf trait in B. rapa , and identified BrrRCO , encoding a HD-Zip transcription factor, as the casual gene underlying lobed leaf formation in B. rapa. Genotyping analysis showed that abundant variations in promoter of BrrRCO is responsible for leaf lobe variation, and the expression levels and promoter activity were significantly affected by the promoter variations between two parents. BrrRCO was a nucleus-specific protein and possess highest expression level at the bases of each lobe. Ectopic overexpression of BrrRCO in Arabidopsis led to deeply lobed leaves have never been seen in wild type, and leaf lobe development was blocked when BrrRCO expression was down-regulated through virus-induced gene silencing assays. Taken together, our findings revealed that BrrRCO positively regulate leaf lobe formation in Chinese cabbage, and the cis-regulatory element modifications result in functional variation of BrrRC O, providing a novel insight into the leaf shape improvement in Chinese cabbage and other Brassica species. Highlight: BrrRCO is essential for leaf lobe formation by repressing local growth of leaf margin cells in B. rapa , and cis-regulatory modifications cause the different allele effects.

Summary: The plant cell wall is the first line of defence against physical damage and pathogen attack. Wall‐associated kinase (WAK) has the ability to perceive the changes in the cell wall matrix and transform signals into the cytoplasm, being involved in plant development and the defence response. Downy mildew, caused by Hyaloperonospora brassicae, can result in a massive loss in Chinese cabbage (Brassica rapa L. ssp. pekinensis) production. Herein, we identified a candidate resistant WAK gene, BrWAK1, in a major resistant quantitative trait locus, using a double haploid population derived from resistant inbred line T12–19 and the susceptible line 91–112. The expression of BrWAK1 could be induced by salicylic acid and pathogen inoculation. Expression of BrWAK1 in 91–112 could significantly enhance resistance to the pathogen, while truncating BrWAK1 in T12–19 increased disease susceptibility. Variation in the extracellular galacturonan binding (GUB) domain of BrWAK1 was found to mainly confer resistance to downy mildew in T12–19. Moreover, BrWAK1 was proved to interact with BrBAK1 (brassinosteroid insensitive 1 associated kinase), resulting in the activation of the downstream mitogen‐activated protein kinase (MAPK) cascade to trigger the defence response. BrWAK1 is the first identified and thoroughly characterized WAK gene conferring disease resistance in Chinese cabbage, and the plant biomass is not significantly influenced by BrWAK1, which will greatly accelerate Chinese cabbage breeding for downy mildew resistance.

Carotenoids were synthesized in the plant cells involved in photosynthesis and photo-protection. In humans, carotenoids are essential as dietary antioxidants and vitamin A precursors. Brassica crops are the major sources of nutritionally important dietary carotenoids. Recent studies have unraveled the major genetic components in the carotenoid metabolic pathway in Brassica, including the identification of key factors that directly participate or regulate carotenoid biosynthesis. However, recent genetic advances and the complexity of the mechanism and regulation of Brassica carotenoid accumulation have not been reviewed. Herein, we reviewed the recent progress regarding Brassica carotenoids from the perspective of forward genetics, discussed biotechnological implications and provided new perspectives on how to transfer the knowledge of carotenoid research in Brassica to the crop breeding process.

Purple heading Chinese cabbage has become popular in recent years due to its attractive color and health benefits. However, purple varieties remain rare, and the regulation mechanism of anthocyanin accumulation in Chinese cabbage is still largely unknown. By introducing the purple color trait from Brassica juncea, a new purple heading Chinese cabbage cultivar (18M-245) was generated with deep purple leaves at both the seedling and adult stages. Anthocyanin accumulation in 18M-245 increased when grown at low temperatures. FISH and genotyping results showed that the purple trait was caused by an alien chromosome addition line derived from the Brassica B genome. The LDOX coding gene BjuB014115 from the addition line was highly expressed in 18M-245, consistent with the results of anthocyanin accumulation. Meanwhile, several MYB and bHLH transcriptional factors from the Brassica A genome were found to directly bind to the promoter of BjuB014115, suggesting that interactions between the Brassica A and B genomes are involved in the regulatory network of anthocyanin biosynthesis in Chinese cabbage. Our results provide new insights into the regulation mechanism of anthocyanin biosynthesis in purple heading Chinese cabbage.