Chinese cabbage (Brassica rapa L. ssp. pekinensis) is an important leafy vegetable crop cultivated worldwide. Drought is one of the most important limiting factors for the growth, production and quality of Chinese cabbage due to its weak drought tolerance. In order to deepen the understanding of drought stress response in Chinese cabbage, metabolomics studies were conducted in drought−tolerant (DT) and drought−susceptible (DS) genotypes of Chinese cabbage under water deficit−simulated mild and severe drought stress conditions. A total of 777 metabolites were detected, wherein 90 of them were proposed as the drought−responsive metabolites in Chinese cabbage, with abscisic acid (ABA), serine, choline alfoscerate, and sphingosine as potential representative drought stress biomarkers. We also found that drought−tolerant and drought−susceptible genotypes showed differential metabolic accumulation patterns with contrasting drought response mechanisms. Notably, constitutively high levels of ABA and glutathione were detected in drought−tolerant genotype in all tested and control conditions. In addition, proline, sucrose, γ−aminobutyric acid, and glutathione were also found to be highly correlated to drought tolerance. This study is the first metabolomic study on how Chinese cabbage responds to drought stress, and could provide insights on how to develop and cultivate new drought−resistant varieties.

Aliphatic glucosinolates are a large group of plant secondary metabolites characteristic of Brassica, including model plant Arabidopsis. The diverse and complex degradation products of the aliphatic glucosinolates contribute to the plants’ responses to herbivory, pathogen attack and environmental stresses. Most of the biosynthesis genes in aliphatic glucosinolate pathway had been cloned, and the research focus recently shifted to the regulatory mechanisms controlling aliphatic glucosinolates accumulation. Until now, more than 40 transcriptional regulators were identified to regulate the aliphatic glucosinolates pathway, however much more novel regulators likely remain to be discovered based on the research evidences over the past decade. In this current study, we took a systemic approach to functionally test 155 candidate transcription factors identified by yeast one-hybrid assay, and successfully validated at least 30 novel regulators that could significantly influence the accumulation of aliphatic glucosinolates in our experiment setup. We also showed that the regulators of aliphatic glucosinolates pathway have balanced positive and negative effects, and the glucosinolates metabolism and plant development could coordinate together. Our work is the largest scale effort so far to validate transcriptional regulators of a plant secondary metabolism pathway, and provides new insights of how the highly diverse plant secondary metabolisms are regulated at transcriptional level.

Walnuts (Juglans regia L.) are an economically important woody crop, but spring frost poses a serious threat to their growth and productivity. However, the molecular mechanisms underlying walnut responses to freezing stress remain largely unknown. In this study, transcriptome analyses were performed on cold-tolerant and cold-sensitive walnut varieties subjected to freezing stress. A total of 9611 differentially expressed genes (DEGs) responsive to freezing stress were obtained, of which 2853 were common up-regulated and 2880 were common down-regulated in both varieties. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed 15 significantly enriched pathways in both varieties, including flavonoid biosynthesis. A simplified walnut flavonoid biosynthesis pathway was constructed, encompassing 36 DEGs encoding 13 key enzymes, demonstrating that flavonoid biosynthesis in walnut is significantly activated under freezing stress. Furthermore, weighted gene co-expression network analysis (WGCNA) identified a regulatory network centered on the JrCBF genes and uncovered 34 potential interacting genes. Collectively, these findings provide novel insights into the molecular responses of walnut to freezing stress and establish a foundation for elucidating the mechanisms underlying walnut cold tolerance.