plant surface microbiology.pdf

6 Signalling in the Rhizobia–Legumes Symbiosis
Dietrich Werner
1 Introduction
During the last few years, significant progress has been made in the understanding
of signal production, signal perception and signal regulation in
plants, microorganisms and animals. In mammalian systems, the notch signal
regulation has been studied intensively with a number of proteins involved in
the signal transport and the proteolytic modifications of the notch signals
(Fig. 1). The involvement of several organelles such as lysosomes, endoplasmic
reticulum and the Golgi network points to interesting similarities and
differences to the signalling across and through the symbiosome membrane
(Werner 1992). Four different mammalian notch homologues have been identified
(Baron et al. 2002). The integrin-adhesion-receptor signalling is another
surface related crosstalk in multicellular organisms (Schwartz and Ginsberg
2002). The cell adhesion involving integrins leads to a phosphorylation of different
growth-factor receptors, including those for the fibroblast growth factor,
the hepatocyte growth factor and the epidermal growth factor (Giancotti
and Ruoslahti 1999).Very recently, a plant receptor-like kinase has been identified
in the laboratory of Martin Parniske, The Sainsbury Laboratory, UK,
which is required for the rhizobial legume symbiosis as well as for the arbuscular
mycorrhiza symbiosis (Stracke et al. 2002). The SYMRK (symbiosis
receptor-like kinase) genes have been studied and characterized in Lotus and
in pea. The protein has a signal peptide, a transmembrane and an extracellular
protein kinase domain. The SYMRK is part of a symbiotic signal transduction
pathway with the perception of a microbial signal molecule, leading
to a rapid symbiosis-related gene activation. In Medicago sativa,a “nodulation
receptor kinase” NORK was identified with a predicted function in Nod-factor
perception/transduction (Endre et al. 2002).
Besides the short-distance signalling between microorganisms and plant
surfaces, long-distance signalling also affects the plant partner of the interaction.
Using mutants of Arabidopsis, the role for long-chain fatty acids in cellto-cell
communication has been established and the plant hormones abscisic
Plant Surface Microbiology
A.Varma, L. Abbott, D. Werner, R. Hampp (Eds.)
© Springer-Verlag Berlin Heidelberg 2004