Tomomi Nakagawa: How do host plants establish secure endo-symbioses with microbial partners?
Date:
Jul 24, 2017
Time:
11:00 AM - 12:00 PM (Local Time Germany)
Speaker:
Tomomi Nakagawa
National Institute of Basic Biology/ Nagoya
Univ.
Location:
MPIPZ
Room:
Lecture hall
Host:
Kenichi Tsuda
Many terrestrial plants accept beneficial microbes inside their
tissues, and also often inside the cell, and establish mutualistic
symbioses. In most of these symbioses, host plants supply photosynthates
in exchange for microbial duties such as a supply of nitrogen nutrients or
phosphates. On the other hand, parasitic microbes also infect plant
tissues and deprive the host of nutrients. To prevent an invasion of these
pathogens, plants exploit multi-layered defense mechanisms, although
rapidly-evolving pathogens often circumvent these and cause disease. My
research interest is "How host plants accept beneficial microbial partners
while rejecting pathogens". In this seminar, I will introduce our recent
studies and discuss the two following topics: security against pathogenic
accesses to host symbiotic systems, a host mechanism to prevent symbiont
cheating in legume-rhizobia symbiosis.
Plant receptor kinase, CERK1, is essential for the perception of
fungal and bacterial cell wall components, chitin oligosaccharides and
peptidoglycan, respectively, and triggers immune responses. In addition,
pathogens often target CERK1 to circumvent host immunity by avirulence
proteins. Thus, CERK1 plays key roles for plant security mechanisms.
However, recently, we found that rice OsCERK1 regulates not only immune
responses but also acceptance of beneficial arbuscular mycorrhizal (AM)
fungi. The contrasting bifunctionality of CERK1 for both eliminating and
accepting microbes seem to be common among terrestrial plants accepting AM
fungi. I will discuss the potential meaning of this bifunctionality of
CERK1.
Legumes establish a mutualistic symbiosis with soil bacteria
called rhizobia and develop nodules on roots. Inside the nodules, rhizobia
fix atmospheric nitrogen to ammonia and supply it to the host plants in
exchange for photosynthates. Host legumes recognize their symbiotic
partners by Nod factors (NFs), symbiotic signal molecules secreted from
rhizobia. However, NFs alone cannot guarantee the rhizobial nitrogen
fixation because the genes involved in NF-synthesis or -secretion are
independent from nitrogen fixation activity. How host legumes manage the
risk of partner rhizobia cheating is largely unclear. I will discuss the
host mechanism for this problem based on our recent findings