CYCLOPS, a mediator of symbiotic intracellular accommodation.
The initiation of intracellular infection of legume roots by symbiotic rhizobia bacteria and arbuscular mycorrhiza (AM) fungi is preceded by the induction of calcium signatures in and around the nucleus of root epidermal cells. Although a calcium and calmodulin-dependent kinase (CCaMK) is a key mediator of symbiotic root responses, the decoding of the calcium signal and the molecular events downstream are only poorly understood. Here, we characterize Lotus japonicus cyclops mutants on which microbial infection was severely inhibited. In contrast, nodule organogenesis was initiated in response to rhizobia, but arrested prematurely. This arrest was overcome when a deregulated CCaMK mutant version was introduced into cyclops mutants, conferring the development of full-sized, spontaneous nodules. Because cyclops mutants block symbiotic infection but are competent for nodule development, they reveal a bifurcation of signal transduction downstream of CCaMK. We identified CYCLOPS by positional cloning. CYCLOPS carries a functional nuclear localization signal and a predicted coiled-coil domain. We observed colocalization and physical interaction between CCaMK and CYCLOPS in plant and yeast cell nuclei in the absence of symbiotic stimulation. Importantly, CYCLOPS is a phosphorylation substrate of CCaMK in vitro. Cyclops mutants of rice were impaired in AM, and rice CYCLOPS could restore symbiosis in Lotus cyclops mutants, indicating a functional conservation across angiosperms. Our results suggest that CYCLOPS forms an ancient, preassembled signal transduction complex with CCaMK that is specifically required for infection, whereas organogenesis likely requires additional yet-to-be identified CCaMK interactors or substrates.
Yano
Koji
K
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Yoshida
Satoko
S
Müller
Judith
J
Singh
Sylvia
S
Banba
Mari
M
Vickers
Kate
K
Markmann
Katharina
K
White
Catharine
C
Schuller
Bettina
B
Sato
Shusei
S
Asamizu
Erika
E
Tabata
Satoshi
S
Murooka
Yoshikatsu
Y
Perry
Jillian
J
Wang
Trevor L
TL
Kawaguchi
Masayoshi
M
Imaizumi-Anraku
Haruko
H
Hayashi
Makoto
M
Parniske
Martin
M
D020013:Calcium Signaling; D007887:Fabaceae / Q000382:microbiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000145:classification / Q000235:genetics / Q000502:physiology*; D000070116:Lotus / Q000382:microbiology / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals; D012275:Oryza / Q000737:chemistry; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012230:Rhizobiaceae / Q000502:physiology; D015398:Signal Transduction; D013559:Symbiosis / Q000235:genetics*
D047908:Intracellular Signaling Peptides and Proteins; D019913:Nuclear Localization Signals; D010940:Plant Proteins