Extended: Cell integrity maintenance during hormone induced cell expansion

Brassinosteroid (BR) is a growth-promoting hormone that regulates cell elongation to facilitate tissue morphogenesis in Arabidopsis thaliana. In plant cells, expansion is driven by inside turgor that exerts pressure on cell wall in outward direction. The cell wall is continuously under surveillance to detect wear and tear occurring in rapidly expanding cells by cell wall integrity (CWI) machinery. In response to any damage in cell wall, CWI machinery activates down -stream cascade for repair and fortification of cell wall. CWI signaling coordinates with the BR signaling to accommodate cell expansion and maintain the cellular architecture. However, the underlying molecular mechanisms have not been explored. Here, we show that BR directly regulates cell integrity by modulating the activity of the cell integrity component FERONIA (FER). The FER knockout mutant exhibited enhanced cell bursting and death in a dose- and time-dependent manner in the presence of exogenous brassinolide. Moreover, downstream target of BR, GSK3 kinase BIN2 directly interacts with and phosphorylates FER. Bikinin (BIN2 inhibitor) treatment results in the accumulation and translocation of FER. We hypothesized that BR regulates cell integrity by controlling FER.