Chinese cabbage (Brassica rapa subsp. pekinensis) is an important leafy vegetable in the Brassica genus of the Brassicaceae family. The size of its edible leaves is an essential trait that determines its economic and nutritional values. However, the current understanding of leaf development in Chinese cabbage remains limited. Here, through forward genetic analysis of the mutant mini24 with defective leaf and root development, we identified the BrRRG gene, which regulates cell division in Chinese cabbage by map-based cloning. We demonstrated that BrRRG impacts leaf size by regulating the expression of E2Fa transcription factors and cell cycle-related genes in Chinese cabbage. Furthermore, BrRRG was found to modulate Chinese cabbage’s response to auxin (indole-3-acetic acid, IAA) and cytokinins hormones, revealing a distinct regulatory mechanism by which BrRRG coordinates the development of underground roots and aboveground leaves. Thus, these results indicate that mutation in BrRRG impairs the growth and development of Chinese cabbage.

Leaf curling is a key agronomic trait that promotes the formation of leafy heads in heading vegetable crops. However, the role of auxin in regulating leaf curling in Chinese cabbage remains largely unknown. In this study, we identified a Chinese cabbage mutant, lic86, which exhibited inward leaf curling and displayed significantly increased transverse curvature indices compared to the wild type. Additionally, among the measured hormones the concentration of indole-3-acetic acid (IAA) was significantly reduced in lic86. Exogenous application of IAA caused outward leaf curling, whereas applying the auxin transport inhibitor, TIBA, resulted in inward leaf curling in both wild type and lic86 plants. Transcriptomic analysis revealed that the differentially expressed genes between WT and lic86 were predominantly associated with hormone signal transduction pathways. Notably, the expression levels of two Brassica rapa asymmetric leaves1 (BrAS1) homologs were significantly elevated in lic86, while the expression of B. rapa LIKE-AUX1 (BrLAX1), the auxin influx carrier gene, was markedly downregulated compared to WT plants. Virus-induced gene silencing of BrLAX1 in WT plants resulted in leaf inward curvature, whereas silencing of BrAS1s in lic86 seedlings led to flattened leaf morphology. These findings offer insights into the molecular mechanism underlying leaf curling and leafy head development in Chinese cabbage.

Leaf color directly affects the appearance quality and nutritional quality of leafy vegetables, thereby determining their economic value. Here, we identified a golden leaf mutant, Mut298, from an ethyl methanesulfonate (EMS)-induced mutant library of Chinese cabbage. Through the approach of forward genetics, it has been demonstrated that the phenotype of Mut298 is due to a single nucleotide substitution from C to T that changes glycine to arginine in the conserved domain of BrPRPL1, which encodes the large subunit ribosomal protein L1 of the chloroplast. Because the PRPL1 mutation causes embryonic lethality in Arabidopsis, the function of PRPL1 in leaf development remains elusive. In this study, the mutation of BrPRPL1 causes a substantial reduction in the expression of key chloroplast-encoded proteins (RbcL, PsaA, and PsaB) and disrupts chloroplast development. Moreover, the chlorophyll content and photosynthetic parameters are significantly lower in Mut298 plants than in wild-type plants, resulting in golden yellow leaves in Chinese cabbage. This study reveals the impact of PRPL1 mutation on ribosome translation within chloroplasts and provides a theoretical a foundation for future research into the regulatory roles of PRPL1 in plant growth and development.

Chinese cabbage (Brassica rapa ssp. pekinensis) has a long cultivation history and is one of the vegetable crops with the largest cultivation area in China. However, salt stress severely damages photosynthesis and hormone metabolism, nutritional balances, and results in ion toxicity in plants. To better understand the mechanisms of salt-induced growth inhibition in Chinese cabbage, RNA-seq and physiological index determination were conducted to explore the impacts of salt stress on carbon cycle metabolism and photosynthesis in Chinese cabbage. Here, we found that the number of thylakoids and grana lamellae and the content of starch granules and chlorophyll in the leaves of Chinese cabbage under salt stress showed a time-dependent response, first increasing and then decreasing. Chinese cabbage increased the transcript levels of genes related to the photosynthetic apparatus and carbon metabolism under salt stress, probably in an attempt to alleviate damage to the photosynthetic system and enhance CO₂ fixation and energy metabolism. The transcription of genes related to starch and sucrose synthesis and degradation were also enhanced; this might have been an attempt to maintain intracellular osmotic pressure by increasing soluble sugar concentrations. Soluble sugars could also be used as potential reactive oxygen species (ROS) scavengers, in concert with peroxidase (POD) enzymes, to eliminate ROS that accumulate during metabolic processes. Our study characterizes the synergistic response network of carbon metabolism and photosynthesis under salt stress.