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Inside out: root cortex‐localized LHK1 cytokinin receptor limits epidermal infection of Lotus japonicus roots by Mesorhizobium loti
Author(s) -
Miri Mandana,
Janakirama Preetam,
Huebert Terry,
Ross Loretta,
McDowell Tim,
Orosz Kathleen,
Markmann Katharina,
Szczyglowski Krzysztof
Publication year - 2019
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.15683
Subject(s) - lotus japonicus , biology , microbiology and biotechnology , epidermis (zoology) , root hair , cytokinin , lateral root , arabidopsis , primordium , complementation , rhizobia , root nodule , cortex (anatomy) , nod factor , botany , symbiosis , mutant , gene , neuroscience , genetics , auxin , anatomy , bacteria
Summary During Lotus japonicus – Mesorhizobium loti symbiosis, the LOTUS HISTIDINE KINASE 1 ( LHK 1) cytokinin receptor regulates both the initiation of nodule formation and the scope of root infection. However, the exact spatiotemporal mechanism by which this receptor exerts its symbiotic functions has remained elusive. In this study, we performed cell type‐specific complementation experiments in the hyperinfected lhk1‐1 mutant background, targeting LHK 1 to either the root epidermis or the root cortex. We also utilized various genetic backgrounds to characterize expression of several genes regulating symbiotic infection. We show here that expression of LHK 1 in the root cortex is required and sufficient to regulate both nodule formation and epidermal infections. The LHK 1 ‐dependent signalling that restricts subsequent infection events is triggered before initial cell divisions for nodule primordium formation. We also demonstrate that AHK 4 , the Arabidopsis orthologue of LHK 1 , is able to regulate M. loti infection in L. japonicus , suggesting that an endogenous cytokinin receptor could be sufficient for engineering nitrogen‐fixing root nodule symbiosis in nonlegumes. Our data provide experimental evidence for the existence of an LHK 1 ‐dependent root cortex‐to‐epidermis feedback mechanism regulating rhizobial infection. This root‐localized regulatory module functionally links with the systemic autoregulation of nodulation ( AON ) to maintain the homeostasis of symbiotic infection.