| Plants have developed sophisticated defense mechanisms to cope with pathogen-caused diseases. Although host defense and pathogen counter-defense mechanisms have been well studied in herbaceous plants, we know much less about how woody plants protect themselves against pathogen infection. Populus (poplars, Salicaceae) is a widespread tree genus that is of enormous economic and ecological importance worldwide. Poplar trees accumulate high quantities of various polyphenols. I investigate the biosynthesis and accumulation of flavonoids in poplar upon rust fungus (Melampsora larici-populina) infection (Ullah et al. 2017, Plant Physiology). The antifungal activities of pathogen-induced flavonoids, especially the flavan-3-ols, which include the monomeric catechins and the polymeric proanthocyanidins (PA), have been studied in vitro and in planta. Another aspect of my research is to investigate the role of plant hormones in the regulation of phenolic products. For example, we could show that poplar increased the levels of flavan-3-ols and hormones, including salicylic acid (SA), jasmonic acid (JA) and abscisic acid (ABA) in response to pathogen infection. Flavan-3-ol biosynthesis was upregulated by both constitutively elevated and pathogen-induced SA, enhancing poplar resistance to rust. JA, although induced by fungal infection, did not trigger flavan-3-ol accumulation (Ullah et al. 2019, New Phytologist). |
