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micro RNA 172 (miR172) signals epidermal infection and is expressed in cells primed for bacterial invasion in Lotus japonicus roots and nodules
Author(s) -
Holt Dennis B.,
Gupta Vikas,
Meyer Dörte,
Abel Nikolaj B.,
Andersen Stig U.,
Stougaard Jens,
Markmann Katharina
Publication year - 2015
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.13445
Subject(s) - lotus japonicus , biology , rhizobia , lotus , gene , genetics , small rna , rna , transcription factor , microbiology and biotechnology , symbiosis , botany , bacteria , mutant
Summary Legumes interact with rhizobial bacteria to form nitrogen‐fixing root nodules. Host signalling following mutual recognition ensures a specific response, but is only partially understood. Focusing on the stage of epidermal infection with Mesorhizobium loti , we analysed endogenous small RNA s ( sRNA s) of the model legume Lotus japonicus to investigate their involvement in host response regulation. We used Illumina sequencing to annotate the L. japonicus sRNA ‐ome and isolate infection‐responsive sRNA s, followed by candidate‐based functional characterization. Sequences from four libraries revealed 219 novel L. japonicus micro RNA s (mi RNA s) from 114 newly assigned families, and 76 infection‐responsive sRNA s. Unlike infection‐associated coding genes such as NODULE INCEPTION ( NIN ), a micro RNA 172 (miR172) isoform showed strong accumulation in dependency of both Nodulation (Nod) factor and compatible rhizobia. The genetics of miR172 induction support the existence of distinct epidermal and cortical signalling events. MIR 172a promoter activity followed a previously unseen pattern preceding infection thread progression in epidermal and cortical cells. Nodule‐associated miR172a expression was infection‐independent, representing the second of two genetically separable activity waves. The combined data provide a valuable resource for further study, and identify miR172 as an sRNA marking successful epidermal infection. We show that miR172 acts upstream of several APETALA2‐type (AP2) transcription factors, and suggest that it has a role in fine‐tuning AP 2 levels during bacterial symbiosis.