Bol-miR168a is a key regulator of defense responses to Sclerotinia sclerotiorum in Brassica oleracea.

key messageOverexpressing Bol-miR168a in cabbage reduces resistance to Sclerotinia sclerotiorum, highlighting its role in disease susceptibility regulation. miRNA-mediated post-transcriptional regulation plays a central role in regulating physiological processes, including plant growth and development, hormone signal transduction, and stress response. However, the underlying mechanism and function of microRNA-mediated repression, particularly in relation to conferring resistance to S. sclerotiorum, has not been extensively explored. In this study, Bol-miR168a was isolated from cabbage, and its function was identified in transgenic Arabidopsis and cabbage under S. sclerotiorum infection. The miR168a gene promoter contains multiple hormone response and stress response elements, which can be bound and activated by corresponding transcription factors. Expression of the Bol-miR168a was strongly induced during the first 48 h post-inoculation. The overexpression of Bol-miR168a in transgenic cabbage resulted in enhanced sensitivity to S. sclerotiorum infection, as evidenced by decreased antioxidant enzyme activities, reduced phenylalanine ammonia-lyase (PAL) content, and elevated malondialdehyde (MDA) levels. Consistent with this, Bol-miR168a overexpression in Arabidopsis (Arabidopsis thaliana) promoted plant susceptibility to S. sclerotiorum and led to increased their capacity to detoxify reactive oxygen species (ROS) in the leaves. Furthermore, in Bol-miR168a-overexpressing plants, disease-related genes displayed distinct expression patterns in transgenic Arabidopsis and cabbage, highlighting differential regulatory responses to pathogen infection. Taken together, our results suggest that Bol-miR168a played a negative role in regulating the resistance of cabbage to S. sclerotiorum, providing a basis for further investigating how Bol-miR168a regulates resistance to S. sclerotiorum.