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 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.