Bugging the Nucleus

Abstract

Leguminous plants benefit from symbiosis with Rhizobium bacteria to support nitrogen fixation. The bacteria release factors (Nod factors) that stimulate plant receptors that cause developmental changes that promote colonization by the symbiont. Kanamori et al. studied mutants of a Lotus gene, Nup133 , that impaired nodulation (formation of the nodule on the root in which the bacteria reside). One of the early responses of root hair cells to Nod factors is pulsatile increases in the intracellular concentration of free calcium. However, in nup mutants, the authors were unable to detect such calcium oscillations with a calcium-sensitive dye. Positional cloning of Nup133 revealed sequence similarity to yeast and human nucleoporins. A role for NUP133 in general nuclear transport seems unlikely, given that the mutants appeared normal with the exception of impaired symbiosis. However, a green fluorescent protein (GFP)-NUP133 fusion protein expressed in transgenic Lotus roots was localized to the nuclear rim in root cells and root hair cells. The authors speculate that NUP133 may function as a key participant in the signaling pathway from receptors at the cell surface to nuclear events necessary for generation of second messengers that promote nodulation. N. Kanamori, L. H. Madsen, S. Radutoiu, M. Frantescu, E. M. H. Quistgaard, H. Miwa, J. A. Downie, E. K. James, H. H. Felle, L. L. Haaning, T. H. Jensen, S. Sato, Y. Nakamura, S. Tabata, N. Sandal, J. Stougaard, A nucleoporin is required for induction of Ca 2+ spiking in legume nodule development and essential for rhizobial and fungal symbiosis. Proc. Natl. Acad. Sci. U.S.A. 103 , 359-364 (2006). [Abstract] [Full Text]