Principal investigator:

Markmann, Katharina, Dr.,

Universität Tübingen

Zentrum für Molekularbiologie der Pflanzen (ZMBP)

Pflanzenphysiologie

Auf der Morgenstelle 32

72076 Tübingen

Phone: 49 7071 29 73222

E-mail: katharina.markmann@zmbp.uni-tuebingen.de

Summary:

Legumes balance symbiotic interactions with nitrogen-fixing bacteria via a systemic feedback system tightly controlling infection and nodulation events. This host regulatory system, termed autoregulation of nodulation (AON), is key to maintaining the association at a mutualistic state.

Upon bacterial infection, root-derived CLE-peptides translocate to the shoot to activate the leucine-rich repeat receptor-kinase HAR1, a shoot-acting symbiosis suppressor. AON is effected downstream of HAR1 in the root, and the existence of a systemic shoot-derived inhibitor (SDI) signal has long been postulated.

Cytokinin was recently suggested to have SDI-like activity, but how specificity in rootward AON signaling is achieved remains unclear. As miRNAs are highly specific regulators capable of both systemic and cell-to-cell movement in plants, and would fit the biochemical criteria previously defined for SDI-active compounds, we suggest that they are excellent SDI candidates.

In a current project, we identified a shoot-root translocated miRNA (miR2111) that suppresses AON, promoting root susceptibility to bacterial infection in a role complementary to that of a putative SDI. Here, we propose to investigate a candidate miRNA, miR171c, as possible SDI signal. To confirm its SDI-like properties, and identify further SDI-like candidate sRNAs, we plan to perform sRNA sequencing followed by target identification using existing degradome libraries, and functionally analyze the respective miRNA-target nodes. We will further use a marker-based approach to define domains of miR2111-mediated susceptibility control compared to those of AON implementation in roots as symbiosis progresses.