A gene encoding a receptor-like protein kinase in the roots of common beanis differentially regulated in response to pathogens, symbionts and nodulation factors

Using mRNA differential display for healthy or Fusarium-infected roots of c ommon bean (Phaseolus vulgaris L. cv. Saxa), we have isolated a bean cDNA e ncoding a putative receptor-like protein kinase (RLK), designated PvRK20-1, that is induced during pathogen attack. The catalytic domain of the deduce d polypeptide is highly homologous to protein kinases whereas the extracell ular domain shares no similarity to any known RLK, suggesting that PvRK20-1 might represent a new class of RLK. PvRK20-1 mRNA accumulated rapidly and transiently in the roots for 3-6 h upon handling and treatment, probably in response to wounding. Subsequently, transcript levels returned to backgrou nd levels in control roots but started to accumulate again to high levels b etween 9 and 24 h in roots infected with the virulent pathogen Fusarium sol ani f. sp. phaseoli. The transcript remained at control levels or was suppr essed upon infection with the mutualistic symbionts tested, the arbuscular mycorrhizal fungus Glomus mosseae and the nodule-forming bacterium Rhizobiu m tropici. A similar expression pattern was observed when the roots were ch allenged with a nodB mutant strain of R. tropici, unable to nodulate common bean. Surprisingly, PvRK20-1 mRNA accumulation increased in roots treated with purified Nod factors from R. tropici, whereas Nod factors from the non -host strain Rhizobium sp. NGR234 had only little effect. The expression of PVRK20-1 at early stages of plant-microbe interactions is consistent with PVRK20-1 playing a role in the differentiation between mutualistic and anta gonistic symbionts. (C) 1999 Elsevier Science Ireland Ltd. All rights reser ved.