Transcriptomic and Proteomic Analyses Unveil the Role of Nitrogen Metabolism in the Formation of Chinese Cabbage Petiole Spot  
[PERSON]  
1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; [EMAIL_ADDRESS] (P.T.)1 Institute of Vegetables, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China; taopeng-84@163.  
Notably, a novel physiological disease, namely, petiole spot, has occurred among Chinese cabbage in the past four decades. The phenotype comprises numerous sesame-like spots, which are black or blackish brown in color, primarily concentrated in the epidermal cells of the petiole. The size of petiole spot typically ranges from 1 to 2 mm. As the condition worsens, the area and density increase, along with the petiole epidermis cracking or rotting [6; 7]. petiole spot has become a serious threat to the quality of the appearance and the marketability of Chinese cabbage, causing significant losses.  
The disease's occurrence results from a complex interplay between genotype and environmental factors [8]. A fertilizer application experiment showed that elevated nitrogen levels exacerbate petiole spot, leading to an increased density of spots [9]. In addition, the occurrence of petiole spot in Chinese cabbage is also linked to high copper (Cu) levels and low boron (B) levels [10]. Systemic observation in the field found that pH value is also an important influencing factor for disease occurrence. Soil with a pH of 8.0 is particularly suited for the onset of this disease [6]. Other factors such as air temperature, low light levels, soil nutrient levels, and postharvest methods also contribute to development of petiole spot [11]. Significantly, excessive application of nitrogen fertilizer is recognized as a crucial factor, and different forms of nitrogen have various effects, with ammonium nitrogen having a stronger impact than nitrate and amide nitrogen [12]. It is noteworthy that previous research on Chinese cabbage petiole spot mainly focuses on field investigations and physiological experiments and has clarified the influencing factors contributing to the onset of the disease. However, the precise mechanism underlying Chinese cabbage petiole spot remains unclear, and more experimental evidence is needed to confirm this. Although the promotion of Chinese cabbage petiole spot by excessive nitrogen fertilizer is well established, the precise mechanism remains elusive.  
To unravel the intricate mechanisms of Chinese cabbage petiole spot, we meticulously examined the morphology of petiole spot in varieties that are resistant and susceptible to petiole spot. Transcriptome and proteome analyses were employed to identify differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) among resistant and susceptible varieties upon high nitrogen treatment. The findings of our study could provide new insights into breeding strategies for resistance to petiole spot in Chinese cabbage.