Phytohormones are of great significance in plant growth, development, immunity, and stress responses. As one of the promising phytohormones, salicylic acid (SA) is a natural phenolic compound synthesized from chorismate through two distinct pathways mediated by isochorismate synthase and phenylalanine ammonia-lyase, respectively. It plays crucial roles in regulating various biological processes related to plant growth and development, as well as in response to diverse biotic and abiotic stresses. Pathogens and herbivores are the most confronting biotic factors that pose severe threats to plant fitness and crop yield. The significance of SA in defense responses against these biotic stresses has been well addressed in the past decades. This review pays attention to the biosynthesis, metabolism, and signaling pathways of SA, and SA-mediated defense responses against pathogens and herbivores, thereby providing theoretical perspectives on the regulatory mechanism of SA-mediated immunity under biotic stress and improving the plant fitness and resistance to diseases caused by biotic factors.

Tremendous progress has been made in the field of nanomedicine for cancer treatment. However, most of the research to date has been focused on inhibiting primary tumor growth with comparatively less efforts directed towards managing tumor metastasis. Here, we introduce a polymeric conjugate P-DOX-iRGD that not only significantly suppressed primary tumor growth but also substantially inhibited pulmonary metastasis in an orthotopic mouse model of breast cancer. In addition, treatment with P-DOX-iRGD markedly reduced breast cancer-induced splenomegaly and liver hematopoiesis. Interestingly, contrasting results were seen for the free form and polymeric form of DOX in vitro and in vivo, which may be attributed to the enhanced permeability and retention (EPR) effect.