Pakchoi is a kind of nonheading Chinese cabbage being widely cultivated not only in China but also all over Asia. High temperature is a major limiting factor influencing the yield and quality of pakchoi, while the mechanism of pakchoi dealing with high-temperature challenges remains largely elusive. In the present study, we conducted a comparative transcriptomic analysis, which was also validated by qPCR, of the heat-tolerant Xinxiaqing (XXQ) variant and Suzhouqing (SZQ) variant, which are heat-sensitive under high-temperature treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses suggest that high-temperature-induced phytohormones signal transduction, especially auxin signal transduction, regulates the heat responses of pakchoi. Our further investigations imply that high-temperature-activated auxin signal plays a positive role in helping pakchoi deal with high-temperature challenge; IAA-pretreated pakchoi plants exhibited greater resistance to the high-temperature treatment, probably due to the induction of antioxidant activity. In addition, our study also identified six heat shock proteins/factors (HSPs/HSFs) whose up-regulation correlates with the elevated heat tolerance of pakchoi. Notably, among these high-temperature-induced heat-responsive factors, HSP20 and HSP26.5 are under the regulation of auxin signal, and this signal cascade contributes to enhancing the thermostability of pakchoi. In the present study, we identified crucial high-temperature-responsive factors and signaling pathways in pakchoi, which help in understanding the mechanism of pakchoi coping with high-temperature challenge.

Non-heading Chinese cabbage (NHCC) is an important vegetable, and its leaves are harvested for consumption. Thus, the initiation and progression of leaf senescence in NHCC directly impact its yield and quality. In multiple plant species, NAC transcription factors are known to act as critical regulators of leaf senescence. However, in NHCC, the NAC transcription factors contributing to leaf senescence regulation remain to be identified, and the mechanisms underlying dark-induced leaf senescence remain unclear. To explore the molecular mechanisms of leaf senescence in NHCC, we stored NHCC away from light and subsequently examined dark-induced transcriptional alterations via RNA sequencing. Interestingly, three NAC transcription factors, BrNAC047, BrNAC052, and BrNAC104, were found to be potently activated by darkness. Subsequently, the virus-induced gene silencing of BrNAC047, BrNAC052, and BrNAC104 demonstrated that these three NACs act as positive regulators of dark-induced leaf senescence in NHCC. Dual-luciferase assays further confirmed that BrNAC047, BrNAC052, and BrNAC104 directly activate the promoters of certain senescence-associated genes. This study uncovers the molecular signaling pathways governing dark-induced leaf senescence in NHCC, highlighting the role of three key regulators and offering valuable molecular targets for delaying leaf senescence in NHCC.