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A switch in Ca 2+ spiking signature is concomitant with endosymbiotic microbe entry into cortical root cells of Medicago truncatula
Author(s) -
Sieberer Björn J.,
Chabaud Mireille,
Fournier Joëlle,
Timmers Antonius C.J.,
Barker David G.
Publication year - 2012
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2011.04834.x
Subject(s) - medicago truncatula , biology , microbiology and biotechnology , endodermis , botany , symbiosis , bacteria , genetics
Summary Ca 2+ spiking is a central component of a common signaling pathway that is activated in the host epidermis during initial recognition of endosymbiotic microbes. However, it is not known to what extent Ca 2+ signaling also plays a role during subsequent root colonization involving apoplastic transcellular infection. Live‐tissue imaging using calcium cameleon reporters expressed in Medicago truncatula roots has revealed that distinct Ca 2+ oscillatory profiles correlate with specific stages of transcellular cortical infection by both rhizobia and arbuscular mycorrhizal fungi. Outer cortical cells exhibit low‐frequency Ca 2+ spiking during the extensive intracellular remodeling that precedes infection. This appears to be a prerequisite for the formation of either pre‐infection threads or the pre‐penetration apparatus, both of which are fully reversible processes. A transition from low‐ to high‐frequency spiking is concomitant with the initial stages of apoplastic cell entry by both microbes. This high‐frequency spiking is of limited duration in the case of rhizobial infection and is completely switched off by the time transcellular infection by both microsymbionts is completed. The Ca 2+ spiking profiles associated with both rhizobial and arbuscular mycorrhizal cell entry are remarkably similar in terms of periodicity, suggesting that microbe specificity is unlikely to be encoded by the Ca 2+ signature during this particular stage of host infection in the outer cortex. Together, these findings lead to the proposal that tightly regulated Ca 2+ ‐mediated signal transduction is a key player in reprogramming root cell development at the critical stage of commitment to endosymbiotic infection.