Teilprojekt B03: Effector-induced manipulation of host polyamide levels

01/01/2023 to 31/12/2026

Phytopathogenic bacteria inject effector proteins into plant cells that manipulate host processes to increase plant susceptibility. We study Brg11, a transcription factor-like effector from the bacterial root pathogen Ralstonia solanacearum. Upon injection into host cells, Brg11 activates expression of plant arginine decarboxylase (ADC), a rate limiting enzyme of polyamine (PA) biosynthesis. High ADC levels cause an increase in PAs that are conjugated to and possibly cause depletion of hydroxycinnamic acids (HCAs). HCAs are a major component of ligno-suberin polymers that act as inducible physico-chemical barriers against invading microbes. Thus, Brg11 might increase host susceptibility by suppressing synthesis of the ligno- suberin-based defence shield. Brg11-induced PA-HCAs have antimicrobial activity but can be degraded by R. solanacearum, possibly indicating an alternative working model where Brg11 manipulates the host to combat R. solanacearum niche competitors. In the framework of this proposal, we will study Brg11-induced diversity of PAs and PA-derived metabolites and its consequences on host immunity, as well as on compositional diversity of the root microbiome. The expected gain of knowledge will enable us to advance working models that explain how Brg11 promotes infection of plants by R. solanacearum. One technical aim of this project is to establish novel approaches that enable us to specifically study effector target cells rather than bulked infected tissue, since availability of such approaches is likely crucial for functional dissection of microbial effectors that function in the context of plant root tissue.