The nodulation of roots in legumes is a key factor in nitrogen fixation. Working in the leguminous plant Lotus japonica, Tirichine et al. and Murray et al. have identified how the hormone cytokinin fits into the signaling cascade by which leguminous plants establish nitrogen-fixation nodules filled with symbiotic bacteria. Gain-of-function mutation in a cytokinin receptor results in spontaneous formation of bacteria-free nodules, whereas loss of function results in too few nodules despite aggressive formation of bacterial infection threads.
L. Tirichine, N. Sandal, L. H. Madsen, S. Radutoiu, A. S. Albrektsen, S. Sato, E. Asamizu, S. Tabata, J. Stougaard, A gain-of-function mutation in a cytokinin receptor triggers spontaneous root nodule organogenesis. Science 315, 104-107 (2007). [Abstract] [Full Text]
J. D. Murray, B. J. Karas, S. Sato, S. Tabata, L. Amyot, K. Szczyglowski, A cytokinin perception mutant colonized by Rhizobium in the absence of nodule organogenesis. Science 315, 101-104 (2007). [Abstract] [Full Text]