‘Vanilla’ (XQC, brassica variety chinensis) is an important vegetable crop in the Brassica family, named for its strong volatile fragrance. In this study, we report the high-quality chromosome-level genome sequence of XQC. The assembled genome length was determined as 466.11 Mb, with an N50 scaffold of 46.20 Mb. A total of 59.50% repetitive sequences were detected in the XQC genome, including 47 570 genes. Among all examined Brassicaceae species, XQC had the closest relationship with B. rapa QGC (‘QingGengCai’) and B. rapa Pakchoi. Two whole-genome duplication (WGD) events and one recent whole-genome triplication (WGT) event occurred in the XQC genome in addition to an ancient WGT event. The recent WGT was observed to occur during 21.59–24.40 Mya (after evolution rate corrections). Our findings indicate that XQC experienced gene losses and chromosome rearrangements during the genome evolution of XQC. The results of the integrated genomic and transcriptomic analyses revealed critical genes involved in the terpenoid biosynthesis pathway and terpene synthase (TPS) family genes. In summary, we determined a chromosome-level genome of B. rapa XQC and identified the key candidate genes involved in volatile fragrance synthesis. This work can act as a basis for the comparative and functional genomic analysis and molecular breeding of B. rapa in the future.

Previous studies revealed that the type VI secretion system (T6SS) has an essential role in bacterial competition and virulence in many gram-negative bacteria. However, the role of T6SS in virulence in Pectobacterium atrosepticum remains controversial. We examined a closely related strain, PccS1, and discovered that its T6SS comprises a single-copy cluster of 17 core genes with a higher identity to homologs from P. atrosepticum. Through extensive phenotypic and functional analyses of over 220 derivatives of PccS1, we found that three of the five VgrGs could be classified into group I VgrGs. These VgrGs interacted with corresponding DUF4123 domain proteins, which were secreted outside of the membrane and were dependent on either the T6SS or type IV secretion system (T4SS). This interaction directly governed virulence and competition. Meanwhile, supernatant proteomic analyses with strains defective in the T6SS and/or T4SS confirmed that effectors, such as FhaB, were secreted redundantly to control the virulence and suppress host callose deposition in the course of infection. Notably, this redundant secretion mechanism between the T6SS and T4SS is believed to be the first of its kind in bacteria.

The aromatic quality of non-heading Chinese cabbage ( Brassica chinensis L., NHCC) vars Xiangqingcai (XQC), is significantly enhanced when cultivated in China's Suzhou region. To investigate the chemical and molecular basis of this characteristic fragrance, an integrated analysis of volatile organic compounds (VOCs), and transcriptomes from three key Xiangqingcai (XQC) cultivars (black leaf [FB], yellow leaf [FH], and Xiuhuajin [FX]) were performed using headspace solid-phase microextraction/gas chromatography–mass spectrometry (HS-SPME-GC-MS) and RNA sequencing, with Suzhouqing (SZQ) as the control. Comparative analysis identified 56 VOCs with significantly different abundances between the XQC cultivars, and SZQ. Thirteen of these were identified as key aroma-active compounds, belonging to diverse chemical classes including nitriles, terpenes, alkenes, aromatic hydrocarbons, esters, ketones, alcohols, and heterocyclic alkanes. Enrichment analysis indicated that sesquiterpenoid and triterpenoid biosynthesis, phenylalanine metabolism, and sulfur-related metabolism were the primary pathways involved. Critical odorants such as β-caryophyllene, phenylacetaldehyde, and 1,8-cineole were identified as major contributors. Key genes encoding enzymes central to the biosynthesis of these aromatic compounds were also uncovered. This study provides a molecular foundation for understanding aroma regulation in NHCC and offers practical targets for breeding programs aimed at improving flavor quality.