Rhizobium-induced root hair deformation in Arabidopsis thaliana transformed with a legume lectin nucleotide phosphohydrolase and characterization of endogenous apyrases of Arabidopsis thaliana

The specificity of rhizobium-legume symbiosis is determined by the type of rhizobial nodulation factor (Nod factor) and the ability of the host plant to respond to the Nod factor. Previous studies have suggested that a LNP isolated from roots of legume Dolichos biflorus (Db-LNP) plays a role in the initiation of rhizobium-legume symbiosis. The role of Db-LNP in symbiosis was investigated further in non-leguminous plant by transforming Arabidopsis thaliana with the full-length Db-LNP cDNA. Db-LNP was detected on the surface of root epidermal cells and root hairs in three representative transgenic Arabidopsis lines. When exposed to the symbiotic rhizobia of D. biflorus, all three lines responded to the rhizobia by showing induced root hair deformation. The nonsymbiotic rhizobium of D. bioflorus did not induce root hair deformation in the same lines. These findings demonstrated that Db-LNP enables the non-leguminous plant, Arabidopsis thaliana, to respond to the symbiotic rhizobia of D. biflorus by showing root hair deformation and provided further evidence that Db-LNP may perceive rhizobial Nod factor and induce root hair deformation in the initiation of rhizobium-legume symbiosis.; No LNP has yet been found in nonlegumes, however, comprehensive studies in Arabidopsis thaliana led to isolation of two LNP-related genes and at least three other apyrase or NTPDase genes. The Arabidopsis NTPDases were divided into three classes that are distinguished by intron-exon boundaries of their genes and structures of their proteins including membrane topology. LNPs may arise from gene duplication of existing Class I NTPDases in plants. All five NTPDases in Arabidopsis were expressed in most organs of Arabidopsis plants; however, cellular localizations of Class I NTPDases in Arabidopsis roots differed from those of legume LNPs. Two representative NTPDases from Class I and Class II NTPDases in Arabidopsis were not found to have carbohydrate-binding activities when heterologously expressed in insect cells. Functional studies of these NTPDases may lead to a better understanding of the role of LNP in Nod factor signaling.