Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Published on September 23, 2005; 10.1104/pp.105.061705

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Received February 21, 2005
Returned for revision June 14, 2005
Accepted June 19, 2005

Nod Factors Induce Nod Factor Cleaving Enzymes in Pea Roots. Genetic and Pharmacological Approaches Indicate Different Activation Mechanisms

Alexandra O. Ovtsyna , Elena A. Dolgikh , Alexandra S. Kilanova , Viktor E. Tsyganov , Alexey Y. Borisov , Igor A. Tikhonovich , and Christian Staehelin *

All-Russia Research Institute for Agricultural Microbiology, 196608 St. Petersburg, Pushkin, Russia
St. Petersburg State University, 199034 St. Petersburg, Russia
State Key Laboratory of Biocontrol, School of Life Sciences, SunYat-Sen (Zhongshan) University, Guangzhou 510275, China

* Corresponding author; email: lsdcs{at}zsu.edu.cn.

Establishment of symbiosis between legumes and rhizobia requires bacterial Nod factors (NFs). The concentration of these lipochitooligosaccharides in the rhizosphere is influenced by plant enzymes. NFs induce on pea (Pisum sativum) a particular extracellular NF hydrolase that releases lipodisaccharides from NFs from Sinorhizobium meliloti. Here, we investigated the ability of non-nodulating pea mutants to respond to NodRlv factors (NFs from Rhizobium leguminosarum bv viciae) with enhanced NF hydrolase activity. Mutants defective in the symbiotic genes sym10, sym8, sym19, and sym9/sym30 did not exhibit any stimulation of the NF hydrolase, indicating that the enzyme is induced via an NF signal transduction pathway that includes calcium spiking (transient increases in intracellular Ca2+ levels). Interestingly, the NF hydrolase activity in these sym mutants was even lower than in wild-type peas, which were not pretreated with NodRlv factors. Activation of the NF hydrolase in wild-type plants was a specific response to NodRlv factors. The induction of the NF hydrolase was blocked by {alpha}-amanitin, cycloheximide, tunicamycin, EGTA, U73122, and calyculin A. Inhibitory effects, albeit weaker, were also found for brefeldin A, BHQ and ethephon. In addition to this NF hydrolase, NFs and stress-related signals (ethylene and salicylic acid) stimulated a pea chitinase that released lipotrisaccharides from pentameric NFs from S. meliloti. NodRlv factors failed to stimulate the chitinase in mutants defective in the sym10 and sym8 genes, whereas other mutants (e.g. mutated in the sym19 gene) retained their ability to increase the chitinase activity. These findings indicate that calcium spiking is not implicated in stimulation of the chitinase. We suggest that downstream of Sym8, a stress-related signal transduction pathway branches off from the NF signal transduction pathway.






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