Simultaneous Integration of Plant Steroid Signaling and Immunity by a Pair of Cell Surface Receptors    
J. KONG (1), Y. Belkhadir (2), E. Smakowska (2) (1) Gregor Mendel institute, Austria; (2) Gregor Mendel Institute, Austria

The first layer of plant immunity is controlled by cell surface receptors of the receptor-like kinases (RLKs) and receptor-like proteins (RLPs) families. The RLK BRI1, control the activities of the growth-promoting hormone Brassinosteroids (BR) at the cell surface. Thus signaling pathways controlling growth and defense systems are initiated at the cell surface. The activities of the BR signaling pathway are also required for appropriate defense responses. Yet, the crosstalk between BR-dependent growth and plant immune systems at the cell surface is largely uncharacterized. BRI1 and several other Pattern Recognition Receptors (PRRs) of the LRR-RK family share the co-receptor BAK1 for optimal function. To date, a handful of RLPs have been shown to impact the outcome of a plant-pathogen interaction, BR signaling and cell wall homeostasis. Here, by monitoring the BR sensitivity of 570 natural Arabidopsis accessions in a genome-wide association study (GWAS) we identified BRN1 and BRN2, two genes coding for RLPs. We show that BRN1 and BRN2 distribute to the plasma membrane (PM) and the endoplasmic reticulum (ER). We implicate BRN2 but not BRN1 in defense responses. We further establish that BRN1 and BRN2 negatively regulate BR signaling and interact with BAK1. Finally, we show that brn1 and brn2 plants are affected in cell wall integrity signaling. The negative regulation of BR signaling and defects in cell wall integrity signaling possibly goes through the multilateral interactions of BRN1/2, BAK1 and BR receptors. We propose that tradeoffs between BR-dependent plant growth and plant immunity ultimately converge on the plant cell wall.

Abstract Number: P15-429
Session Type: Poster